LaMg6Ga6S16: a chemical stable divalent lanthanide chalcogenide

Abstract

Divalent lanthanide inorganic compounds can exhibit unique electronic configurations and physicochemical properties, yet their synthesis remains a great challenge because of the weak chemical stability. To the best of our knowledge, although several lanthanide monoxides epitaxial thin films have been reported, there is no chemically stable crystalline divalent lanthanide chalcogenide synthesized up to now. Herein, by using octahedra coupling tetrahedra single/double chains to construct an octahedral crystal field, we synthesized the stable crystalline La(II)-chalcogenide, LaMg6Ga6S16. The nature of the divalent La²⁺ cations can be identified by X-ray photoelectron spectroscopy, X-ray absorption near-edge structure and electron paramagnetic resonance, while the stability is confirmed by the differential thermal scanning, in-situ variable-temperature powder X-ray diffraction and a series of solid-state reactions. Owing to the particular electronic characteristics of La²⁺(5d¹), LaMg6Ga6S16 displays an ultrabroad-band green emission at 500 nm, which is the inaugural instance of La(II)-based compounds demonstrating luminescent properties. Furthermore, as LaMg6Ga6S16 crystallizes in the non-centrosymmetric space group, P−6, it is the second-harmonic generation (SHG) active, possessing a comparable SHG response with classical AgGaS2. In consideration of its wider band gap (Eg = 3.0 eV) and higher laser-induced damage threshold (5×AgGaS2), LaMg6Ga6S16 is also a promising nonlinear optical material.

Full text

Article https://doi.org/10.1038/s41467-024-47209-4
LaMg
6
Ga
6
S
16
: a chemical stable divalent
lanthanide chalcogenide
Yujie Zhang
1
,JialeChen
1
, Kaixuan Li
1
, Hongping Wu
1
,ZhangguiHu
1
, Jiyang Wang
1
,
Yicheng Wu
1
& Hongwei Yu
1
Divalent lanthanide inorganic compounds can exhibit unique electronic con-
figurations and physicochemical properties, yet their synthesis remains a great
challenge because of the weak chemical stability. To the best of our knowl-
edge, although several lanthanide monoxides epitaxial thin films have been
reported, there is no chemically stable crystalline divalent lanthanide chalco-
genide synthesized up to now. Herein, by using octahedra coupling tetrahedra
single/double chains to construct an octahedral crystal field, we synthesized
the stable crystalline La(II)-chalcogenide, LaMg
6
Ga
6
S
16
. The nature of the
divalent La2+ cations can be identified by X-ray photoelectron spectroscopy,
X-ray absorption near-edge structure and electron paramagnetic resonance,
while the stability is confirmed by the differential thermal scanning, in-situ
variable-temperature powder X-ray diffraction and a series of solid-state
reactions. Owing to the particular electronic characteristics of La2+(5d1),
LaMg
6
Ga
6
S
16
displays an ultrabroad-band green emission at 500 nm, which is
the inaugural instance of La(II)-based compounds demonstrating luminescent
properties. Furthermore, as LaMg
6
Ga
6
S
16
crystallizes in the non-
centrosymmetric space group, P−6, it is the second-harmonic generation
(SHG) active, possessing a comparable SHG response with classical AgGaS
2
.In
consideration of its wider band gap (E
g
= 3.0 eV) and higher laser-induced
damage threshold (5×AgGaS
2
), LaMg
6
Ga
6
S
16
is also a promising nonlinear
optical material.
Lanthanide inorganic compounds with low oxidation state (+2) that are
capable of exhibiting intriguing physicochemical properties due to the
presence of outer shell 4for 5dconduction carriers in divalent lan-
thanides ions have showcased the immense potential for application in
various frontier fields such as superconductivity, magnetics,
photoluminescence1–8. However, one intractable drawback to divalent
lanthanide compounds is the chemical stability, which seriously pre-
cludes their development9,10. Recently, although several new types of
divalent lanthanide monoxides epitaxial thin films, including YO and
LaO, have been prepared, the surfaces of these films must be capped
in-situ AlO
x
layer to prevent the oxidation at room temperature9,11.
Thus, synthesizing the chemically stable divalent lanthanide
compounds is still faced by great challenges. To date, as we know, no
any successful stable crystalline divalent lanthanide chalcogenide has
been synthesized.
Based on the first-principles calculations, Li et al. have uncovered
the octahedral crystal field is vitally pivotal for the formation of the
divalent lanthanum in LaO12. We have also noticed that almost all the
divalent lanthanides (Ln2+) in lanthanide monoxides and mono-
chalcogenides are coordinated by six Q (Q= O or S) atoms to formthe
[LnQ
6
]octahedra
4,13. On the contrary, the high-oxidation-state lantha-
nides (Ln3+) is typically found in the high-coordinated [LnQ
x
](x=7or
8) polyhedra, e.g., La
2
S
3
14, LaGaS
3
15,La
2
Ga
2
GeS
8
16,La
6
MgGe
2
S
14
17,
K
3
LaP
2
S
8
18,KYGeS
4
19,20,Ba
3
La
4
O
4
(BO
3
)
3
X(X=F,Cl,Br)
21,whichalso
Received: 25 August 2023
Accepted: 21 March 2024
Check for updates
1
Tianjin Key Laboratory of Functional Crystal Materials, Institute of Functional Crystal, College of Materials Science and Engineering, Tianjin University of
Technology, Tianjin, China. e-mail: yuhw@email.tjut.edu.cn
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conforms to Pauling’s well-known second rule, i.e., high-valence is
favored for high coordination22. On the other hand, Evans and Meyer
et al.’sresearch show that the construction of the proper anionic fra-
meworks in combination with lanthanide cations can enhance chemi-
cal stability by its gain in lattice energy23, as corroborated via the
synthesis of a series of stable divalent lanthanide organic complexes,
including [(18-crown-6)K][(C
5
H
4
SiMe
3
)
3
Y]24, [K(18-crown-6)(OEt
2
)]
[(C
5
H
3
(SiMe
3
)
2
−1,3)
3
La]10, and [K([2.2.2]crypt)][LaCp”
3
](Cp”=1,3-
(SiMe
3
)
2
C
5
H
3
), [2.2.2]crypt=4,7,13,16,21,24-hexaoxa-1,10-diazabicy-
clo[8.8.8]hexacosane)10.
Clearly, the above studies have implied that the strong octahedral
crystal fields and proper anionic framework are crucial for the for-
mation of stable divalent lanthanide compounds. In the recent
research, by adopting octahedra to couple tetrahedra single/double
chains strategy, a stable crystalline [Mg/Ga-S]
∞
anionic framework with
octahedral channel (C
3h
) has been constructed by our group and Pan’s
group25,26, where alkali and alkaline-earth or even other monovalent or
divalent cations can be filled (Fig. 1), and all of the resulting com-
pounds exhibit the similar crystal structures, e.g., AMg
3
M
3
Q
8
(A=Li, Na,
Ag; M=Al, Ga; Q = S, Se) and AeMg
6
Ga
6
S
16
(Ae=Ca, Sr, Ba). Based on
these, we speculated that the framework should be also available for
the syntheses of the divalent lanthanide chalcogenide because of its
particular structural feature and strong accommodating ability for a
wide range of elements and oxidation states. Guided by these ideas, we
introduced the lanthanum (La) into the stable [Mg/Ga-S]
∞
anionic
framework and successfully synthesized the crystalline La(II)-chalco-
genide, LaMg
6
Ga
6
S
16
. In its structure, the stable [Mg/Ga-S]
∞
framework
channels create the strong [LaS
6
] octahedra crystal field, which results
in the formation of stable divalent La2+ possessing the presence of
outer shell 5d1conduction carriers. Interestingly, owing to the unique
electronic characteristics of La2+(5d1), LaMg
6
Ga
6
S
16
exhibits an
ultrabroad-band green emission at 500 nm with an excitation of
360 nm. This is the inaugural instance of La(II)-based compounds to
display luminescent properties. Additionally, as LaMg
6
Ga
6
S
16
crystal-
lizes in the noncentrosymmetric space group of P−6, the excellent
nonlinear optical (NLO) properties are also observed in LaMg
6
Ga
6
S
16
,
including the relatively large second-order harmonic generation (SHG)
response (~0.8×AgGaS
2
), wide band gap (E
g
=3.0eV), high laser-
induced damage threshold (LIDT) (5 × AgGaS
2
), and wide transparent
window (0.41-20 μm). These make LaMg
6
Ga
6
S
16
a promising NLO
crystal. Herein, we will report its synthesis, structure, and luminescent
and NLO properties.
Results and discussion
Experimental synthesis and structure determination of
LaMg
6
Ga
6
S
16
Polycrystalline LaMg
6
Ga
6
S
16
was synthesized through a conventional
solid-state technique in sealed silica tubes at 1233K and the purity of
phase was verified by the powder X-ray diffraction (XRD) (Supple-
mentary Fig. 1). Furthermore, the energy-dispersive spectroscopy
measurement showed the existence of La/Mg/Ga/S, and their average
atomic ratios were approximately equal to the theoretical ones, 3.45%,
20.69%, 20.69%, and 55.12% (Supplementary Fig. 2). Then, the
millimeter-sized single crystals of LaMg
6
Ga
6
S
16
were grown by melting
and re-crystallizing the stoichiometric pure phase. By using these
crystals, the crystal structureof LaMg
6
Ga
6
S
16
was determinedby single
crystal XRD. It indicates that LaMg
6
Ga
6
S
16
crystallizes in the non-
centrosymmetric hexagonal space group P-6(No.174), with cell para-
meters of a= 16.7154(5)Å, c=7.4147(3)Å, andV= 1794.15(13) Å3(Sup-
plementary Table 1). In the asymmetric unit, there are three unique La,
sixuniqueMg,threeuniqueGa,andelevenSatoms(Supplementary
Table 2). The Mg atoms are six-coordinated forming [MgS
6
] octahedra
with the Mg−S distances ranging from 2.482(11) to 2.834(18) Å. All of
the Ga atoms are coordinated by four S atoms to form [GaS
4
] tetra-
hedra, and the Ga-S distances range from 2.226(7) to 2.333(6) Å. The La
atoms are coordinated by six S atoms to form [LaS
6
] octahedra with
La–S distances ranging from 2.963(7) to 2.994(7) Å. All of these dis-
tances (Supplementary Table 3) are consistent with those in other
chalcogenides17,27,28.
The structure of LaMg
6
Ga
6
S
16
isshowninFig.2. Clearly,
LaMg
6
Ga
6
S
16
features a three-dimensional (3D) framework with C
3h
symmetry along the caxis and constructed by the [MgS
6
] octahedra
coupling [GaS
4
] tetrahedra single/double chains (Fig. 2a). In detail, the
MgS
6
octahedra are connected with each other via corner-sharing and
face-sharing (in the a-b plane) and edge-sharing (along the c-axis) to
fabricate a [Mg-S]
∞
framework, as shown in Fig. 2b. While the [GaS
4
]
tetrahedra are connected via corner-sharing to formtwo types of Ga-S
chains along the c-axis, i.e., [Ga(1)S
3
]
∞
single chains (Fig. 2c) and
[Ga(2,3)
2
S
4
]
∞
double chains (Fig. 2d). Furthermore, the resulting [Ga(1)
S
3
]
∞
single chains are connected and fixed in the [Mg-S]
∞
framework by
the Ga-S bonds to create the [Mg/Ga-S]
∞
framework (Fig. 2e), which are
further linked by the [Ga(2,3)
2
S
4
]
∞
double chains to construct the 3D
framework structure of LaMg
6
Ga
6
S
16
. The La atoms fill the channel-like
cavities of the 3D framework to balance the residual charges (Fig. 2f).
Interestingly, the La atoms in LaMg
6
Ga
6
S
16
exhibit the scarcely
seen divalent state (+2), which was only reported in three metastable
inorganic compounds LaO, LaS and LaS
2
with multiple phase transi-
tions (α:P2
1
/b; β:Pnam;γ:P4/nmm)29,30 and two organic complexes
[K(18-crown-6)(OEt
2
)][(C
5
H
3
(SiMe
3
)
2
−1,3)
3
La] and [K([2.2.2]crypt)]
[LaCp”3](Cp”=1,3-(SiMe
3
)
2
C
5
H
3
), [2.2.2]crypt=4,7,13,16,21,24-hex-
aoxa-1,10-diazabicyclo[8.8.8]hexacosane)4,9,10. To ascertain the oxida-
tion state of La2+ in LaMg
6
Ga
6
S
16
, X-ray photoelectron spectroscopy
(XPS) measurement and analysis for La metal, LaMg
6
Ga
6
S
16
,andLa
2
S
3
were conducted and demonstrated, as shown in Fig. 3a. The results
show that the peak position of La 3d
3/2
(851.5 eV) and 3d
5/2
(834.1 eV) in
LaMg
6
Ga
6
S
16
is located between those of La 3d
3/2
(851.7 eV) and 3d
5/2
(834.9 eV) in La metal (La0)andLa3d
3/2
(851.2 eV) and 3d
5/2
(833.7 eV)
in La
2
S
3
(La3+), suggesting the divalent state (+2) of La in LaMg
6
Ga
6
S
16
9.
To better characterize the chemical valence of La in LaMg
6
Ga
6
S
16
,the
synchrotron X-ray absorption spectroscopy (XAS) measurements of
LaMg
6
Ga
6
S
16
and La
2
S
3
were performed. As indicated by the La L-edge
X-ray absorption near-edge structure (XANES) spectra (Fig. 3b),
LaMg
6
Ga
6
S
16
exhibits an absorption edge with energy lower thanthat
of La
2
S
3
, indicating a lower valence stateLa in LaMg
6
Ga
6
S
16
than thatof
La
2
S
3
(+3)31,32. This is in good agreement with the XPS results. Further,
128
144 152
186
197
215 222
100
125
150
175
200
225
250
)mp(suidarcimotA
Cu Ag Li Na Ca Sr Ba
AgS3/CuS3LiS6/NaS6CaS6SrS9/BaS9
C3h
Fig. 1 | The accommodating ability of [Mg/Ga-S]
∞
framework. The accom-
modating ability of [Mg/Ga-S]
∞
framework. Statisticson radius and the coordination
of a range of atoms filled in [Mg/Ga-S]
∞
framework. This framework can be filled
with alkali and alkaline-earth or even other monovalent divalent cations.
Article https://doi.org/10.1038/s41467-024-47209-4
Nature Communications | (2024) 15:2959 2
Content courtesy of Springer Nature, terms of use apply. Rights reserved

[MgS6]
[GaS4]
[LaS6]
[Mg-S]∞framework
[Ga(1)S3]∞chain [Mg/Ga-S]∞framework
[Ga(2,3)2S4]∞chain
c
a
b
Mg
La
Ga
S
(a) (b) (e)
(d)
(c)
(f)
Fig. 2 | Crystal structural features of LaMg
6
Ga
6
S
16
.MgS
6
octahedron, GaS
4
tet-
rahedron, and LaS
6
octahedron a;[Mg-S]
∞
framework b;1D[Ga(1)S
3
]
∞
chain c;
[Ga(2,3)
2
S
4
]
∞
chain d;[Mg/Ga-S]
∞
framework eand structure of LaMg
6
Ga
6
S
16
viewed along the c-axis, the dashed line represent single unit cell f.TheMgS
6
octahedra firstly connect with each other via corner-sharing (in the a-b plane) and
edge-sharing (along the c-axis) to form Mg-S framework with [Ga(1)S
3
]
∞
single
chains connected and fixed in the framework by the Ga-S bonds. Then, these
adjacent open frameworks are further linked by the [Ga(2,3)
2
S
4
]
∞
double chains to
createthe [Mg/Ga-S]
∞
framework. Thecolor codes for theatoms are blue: La,violet:
Mg, red: Ga,grey: S.
(d)
(c)
La
K
Si
O
C
La(II)-based
Organic Complexes
Anion framework
coupling
La(II) cation
LaO LaS
La-centered
[LaS6]
octahedra
4.1394 Å Edge-sharing
C3h -
La
SSS
SSS
7.4147Å
[LaS6]
Octahedral
Crystal Field
(b)
(a)
(e) (f)
5450 5480 5510 5540 5570 5600
0.0
0.3
0.6
0.9
1.2
1.5
1.8
5470 5474 5478 5482 5486
La S
LaMg Ga S
La
La
)stinu.bra(noitprosbadezilamroN
Energy (eV)
La S
LaMg Ga S
1.96 1.98 2.00 2.02 2.04
)
.
u.
a(
yti
s
ne
t
nI
g value
LaMg
6
Ga
6
S
16
g = 2.008
g = 1.980
S vacancies
La2+ (5d1)
Fig. 3 | Identification of La(II) valence states and structural analysis in
LaMg
6
Ga
6
S
16
.La 3dXPS spectrum with fitting curves for the La metal powder,
LaMg
6
Ga
6
S
16
,andLa
2
S
3
a;LaL-edge normalized XANES spectra of LaMg
6
Ga
6
S
16
(red line) and La
2
S
3
(blueline); Inset (fromblack dashed squareregion) givesXANES
spectra between 5470 eV and 5486 eV of LaMg
6
Ga
6
S
16
(red line) and La
2
S
3
(blue
line), the black arrow represents the increase inenergy from low to high b;EPR
spectrum of LaMg
6
Ga
6
S
16
c; Crystal structure of La(II)-based inorganic compounds:
LaO and LaS d, the color codes for the atoms are red:La, blue: O, green: S; Crystal
structure of La(II)-based organic complexes: [K(18-crown-6)(OEt
2
)]
[(C
5
H
3
(SiMe
3
)
2
−1,3)
3
La] e, the pink arrow indicates the coupling between anion
framework and La(II)cation, and the color codes for the atoms arepink: La, yellow:
K, blue: Si, red: O, black: C; [Mg/Ga-S]
∞
framework and the LaS
6
octahedron f,red
triangle indicates the coordination environment of the La atoms, and the color
codes for the atoms are green: La, black: Mg, pink: S.
Article https://doi.org/10.1038/s41467-024-47209-4
Nature Communications | (2024) 15:2959 3
Content courtesy of Springer Nature, terms of use apply. Rights reserved

we also used electron paramagnetic resonance (EPR) to characterize
the La2+ (5d1) in LaMg
6
Ga
6
S
16
sample. As shown in Fig. 3c, a distinct EPR
signal is observed for LaMg
6
Ga
6
S
16
at g= 1.980, which could be
attributed to an unpaired electron interacting strongly with the
nucleus of 139La23. The similar EPR signals have been well-reported on
defective [K(18-crown-6)(OEt
2
)][(C
5
H
3
(SiMe
3
)
2
−1,3)
3
La] and [K([2.2.2]
crypt)][LaCp”3] and can be considered as the signature of the exis-
tence of La2+ 10. In addition, the bond valence sums calculations result
in the values of 1.96–2.13 for La2+,1.80–2.05 for Mg2+, 2.97–3.00 for
Ga3+,and1.82–2.18 for S2- 33. All of these indicate the nature of the
divalent La2+ cations in LaMg
6
Ga
6
S
16
.
Further, the thermal behavior of LaMg
6
Ga
6
S
16
was studied by
differential thermal scanning (DSC) measurements. Clearly, only one
endothermic peak at 1140 °C was observed on the heating DSC curve
(Supplementary Fig. 3), suggesting that LaMg
6
Ga
6
S
16
did not undergo
the decomposition and structural phase transitions when the tem-
perature was increased from room temperature to 1140°C. Moreover,
in-situ variable-temperature powder X-ray diffraction and a series of
solid-statereactionsinthesealedsilicatubeswiththedifferentcalci-
nated temperatures show LaMg
6
Ga
6
S
16
has no phase transition when
its polycrystalline sample was heated from 10K to 1273 K (Supple-
mentary Fig. 4), which also manifest that LaMg
6
Ga
6
S
16
is thermally
stable. Meanwhile, the crystal of LaMg
6
Ga
6
S
16
was placed in the air and
water at room temperature for one week with no decomposition or
degradation observed (Supplementary Fig. 5). In addition, Global
Instability Index (GII) of LaMg
6
Ga
6
S
16
is calculated33,34,andtheresult
(0.088) is lower than 0.2 v.u. That also indicates the structural stability
of LaMg
6
Ga
6
S
16
35–37.
The nature of the stable divalent La2+ cations in LaMg
6
Ga
6
S
16
could be attributed to the unique [Mg/Ga-S]
∞
anionic framework.
Comparing LaMg
6
Ga
6
S
16
with LaO and LaS, it can be seen that these
La2+ cations exhibit the similar coordination features, i.e., La2+ cations
are six-coordinated in LaO
6
or LaS
6
octahedral crystal fields (Fig. 3d),
while the previous studies in LaO also elucidate that octahedral crystal
field is helpful for the formation of divalent lanthanum12. In LaO and
LaS, LaO
6
and LaS
6
octahedra are connected with each other via edge-
sharing to build the whole structure, respectively. According to Paul-
ing’s third rule22, such connections are disadvantageous for structural
stability owing to the increased cation–cation electrostatic repulsion.
Also, the calculated results of their GII show that LaO (0.215) and LaS
(0.349) have greater than 0.2 valence unit (v.u)34, which indicates their
structures are indeed metastable. Importantly, previous research finds
that constructing the proper anionic frameworks to couple lanthanum
cations can enhance the chemical stability of compounds by effec-
tively harnessing the gain in lattice energy23. The formation of both
divalent lanthanum organic complexes is an excellent example to
demonstrate this concept (Fig. 3e). Similar to the case with organic
complexes, we developed a crystalline [Mg/Ga-S]
∞
structural frame-
work by adopting octahedra coupling tetrahedra single/double chains
strategy. Of note, such a framework possesses interconnected struc-
tures in which the neatly arranged [Ga-S] chains were connected by the
[Mg-S] framework via covalent bonds. Such interconnected structure
endowed [Mg/Ga-S]
∞
structural framework with strong chemical sta-
bility, which has also been demonstrated in the reported covalent
organic frameworks38. Additionally, the stable structural framework
can be used as a template to accommodate a series of A atoms (A=Li,
Na, Ca, Sr, Ba, and even La) while spatially confining these atoms into
atomic-scale channels via coordination configurations. In particular,
the coordination bond lengths of A-S are in the range of 2.934–3.138 Å,
which providesa suitable micro-environment for La because the bond
lengths of La-S are about 3.000 Å16,39. More importantly, the crystalline
[Mg/Ga-S]
∞
framework channels possess C
3h
symmetry along the c-
axis, in which the six-coordinated LaS
6
octahedral crystal field can be
created (Fig. 3f). That facilitates the formation of divalent lanthanum
when introducing La into the crystalline [Mg/Ga-S]
∞
anionic
framework. Further, the LaS
6
octahedra in LaMg
6
Ga
6
S
16
are isolated
and aligned arrangements along the c-axis with a longer La-La distance
of 7.4147Å than 4.1394Å in LaS, which greatly reduces electrostatic
repulsion between La2+. These structural attributes of LaMg
6
Ga
6
S
16
will
be able to promote it exhibiting good chemical stability.
Photoluminescence (PL) properties
Given the electronic characteristics of divalent lanthanum, we inves-
tigated the luminescence features of LaMg
6
Ga
6
S
16
.ThePLexcitations
atroomtemperature(298K)weremeasuredundertheexcitationof
340–380nm.AsshowninFig.4a, the optimal excitation wavelength is
about 360 nm. Under the excitation of 360 nm at room temperature,
LaMg
6
Ga
6
S
16
shows anultrabroad-band green emission at 500 nm with
a full width at half maximum (FWHM) of 127nm (Fig. 4b). The ultrab-
road emission band cover almost the whole visible light region and
could find applications in the field of human-centric full-visible-
spectrum lighting40. Meanwhile, this characteristic green emission
under 360 nm excitation endow s LaMg
6
Ga
6
S
16
with the potential light-
emitting diode application under the excitation of commercial near
ultraviolet chips41. Further, to investigate the origin of luminescence
properties, the thermoluminescence (TL) measurement of
LaMg
6
Ga
6
S
16
is performed. As shown in Fig. 4c,thesampleshowsa
very weak TL glow curve in the range of 290K to 450 K, indicating a
low content of defects in LaMg
6
Ga
6
S
16
.Byfitting the TL curve with two
Gaussian bands peaking at 346 K and 384 K, the characteristic trap
depths (E
T
) were estimated to be 0.69 and 0.77eV by using the crude
relationship E
T
=T
m
/500 eV, where T
m
represents the temperature (K)
of the TL fitting peak42,43. In view of the EPR results (g= 2.008) (Fig. 3c),
it is evident that the two trap depths originate from the intrinsic
defects, corresponding to the slight S vacancies defect44,45.Basedon
these studies, the strong green emission observed in LaMg
6
Ga
6
S
16
does not stem from intrinsic defects of exceedingly low content. In
order to find out the origin of PL property of LaMg
6
Ga
6
S
16
, we also
measured the luminescence features of CaMg
6
Ga
6
S
16
and
SrMg
6
Ga
6
S
16
, which are isomorphous to LaMg
6
Ga
6
S
16
with chemical
substitutions from La to Ca or Sr. Experimental results indicate
CaMg
6
Ga
6
S
16
(Fig. 4d) and SrMg
6
Ga
6
S
16
(Supplementary Fig. 6) have
no PL emission. Also, when the polycrystalline samples of
CaMg
6
Ga
6
S
16
,SrMg
6
Ga
6
S
16
and LaMg
6
Ga
6
S
16
were radiated by the UV
irradiation, only LaMg
6
Ga
6
S
16
exhibited the green light emission
(Supplementary Fig. 7). These results suggest that the PL property of
LaMg
6
Ga
6
S
16
shouldcome from the La cations,rather than the[Mg/Ga-
S]
∞
anionic frameworks. But, the previous research46 has confirmed
that the trivalent La3+ cations cannot exhibit luminescent properties
(we also measured the PL spectrum of La
2
S
3
(Supplementary Fig. 8),
which show that La
2
S
3
with the trivalent La3+ cations have no PL
property). So, these results also further indicate the nature of the
divalent La2+ (5d1) cations in LaMg
6
Ga
6
S
16
. Referencing Li’s, et al.first-
principles calculations on the octahedral crystal-field splitting gap
between the upper-lying e
g
and lower-lying t
2g
for the La2+ 5d orbitals in
monoxide LaO, we can conclude that the green emission position at
500 nm in LaMg
6
Ga
6
S
16
should originate from the d-d transition of the
La2+ within the low-coordinated octahedral crystal field, because the
octahedral crystal-fieldsplittinggapfortheLa
2+ 5dorbitals is
approximately 2.50 eV (Fig. 4e)1,10,12,47, which is precisely consistent
with the green emission position at 500nm in LaMg
6
Ga
6
S
16
.
Meanwhile, the decay curve of LaMg
6
Ga
6
S
16
under excitation at
360 nm, monitored at the peak of 500 nm at room temperature is
presented in Fig. 4f. The decay curve can be fitted using a double
exponential decay formula (1)48
IðtÞ=I
0+A
1expðt=τ1Þ+A
2expðt=τ2Þð1Þ
Tave =A
1τ12+A
2τ22

=A1τ1+A
2τ2
 ð2Þ
Article https://doi.org/10.1038/s41467-024-47209-4
Nature Communications | (2024) 15:2959 4
Content courtesy of Springer Nature, terms of use apply. Rights reserved

where I(t) and I
0
denote the luminescence intensity, A
1
and A
2
are the
corresponding fitting constants, and τ
1
and τ
2
are the decay time for an
exponential component. As shown in Fig. 4f, by using the above fitting
equation, the decay time for LaMg
6
Ga
6
S
16
can be fitted to τ
1
=1.32μs
and τ
2
=15.01μs. According to the formula (2)43, the value of average
lifetimes (τ
ave
) was calculated to be 6.63 μs, which is similar to divalent
lanthanide compounds with lifetimes in the microsecond time-range
(0.5–10 μs)1,3,48,49.
From the above discussion, LaMg
6
Ga
6
S
16
not only represents the
inaugural instance of La(II)-based compounds to exhibit PL properties
but also exhibits an ultrabroad-band green emission at 500 nm with
FWHM of 127 nm owing to the d-d transition of the La2+ in the low-
coordinated octahedral crystal field. Inparticular, the FWHM of 127 nm
for LaMg
6
Ga
6
S
16
is larger than the developed rare earth-doped phos-
phor, such as CaY
2
HfAl
4
O
12
:Ce3+ (FWHM: 120 nm)50,β-SiAlON:Yb2+
(FWHM: 66 nm)51,Li
2
SrSiO
4
:Pr3+ (FWHM: 50nm)52,β-SiAlON:Eu2+
(FWHM: 55 nm)53,Ca
3
SiO
4
Cl
2
:Eu2+ (FWHM: 59 nm)54,
Ba
2
CaZn
2
Si
6
O
17
:Eu2+ (FWHM: 80 nm)55,Ba
3
Si
6
O
12
N
2
:Eu2+ (FWHM:
75 nm)56,andCa
10
Na(PO
4
)
7
:Eu2+ (FWHM: 80 nm)57. More importantly,
such an ultrabroad FWHM will be helpful its applications in 3D sensing,
food analyzing, and other specificfields1,40.
NLO properties
Since LaMg
6
Ga
6
S
16
belongs to the non-centrosymmetric class and
features the stable [Mg/Ga-S]
∞
frameworks constructed by the NLO-
active [GaS
4
]tetrahedraand[MgS
6
] octahedra, the NLO properties are
also investigated. As a result, LaMg
6
Ga
6
S
16
shows a phase-matchable
(PM) SHG response of 0.8×AgGaS
2
@2090 nm (Fig. 5a and Supple-
mentary Table 4)58–60. The birefringence of LaMg
6
Ga
6
S
16
was also
measured on a plate-shaped crystal. It indicates that the birefringence
of LaMg
6
Ga
6
S
16
at visible light is 0.041 (Fig. 5b and Supplementary
Fig. 9)61,62. Meanwhile, the ultraviolet–vis–NIR diffusion spectrum
shows that the band gap of LaMg
6
Ga
6
S
16
is 3.0 eV (Fig. 5c). The rela-
tively large band gap causes LaMg
6
Ga
6
S
16
to generate a high powder
LIDT (~105 MW·cm−2)63–65, which is more than five times that of AgGaS
2
(~20 MW·cm−2)66. Furthermore, Fourier transformation infrared (IR)
(Fig. 5d) and Raman spectra (Fig. 5e) indicates that LaMg
6
Ga
6
S
16
has no
obvious absorption in a wide IR range from 4000 to 500cm−1(i.e.,
2.5 ~ 20 μm). Especially, compared with commercial AgGaS
2
and other
important IR NLO crystals, LaMg
6
Ga
6
S
16
exhibits well-balanced NLO
properties, including wide transmission region and band gaps, high
LIDT, moderate birefringence as well as PM SHGresponses (Fig. 5fand
Supplementary Table 5). These suggest that LaMg
6
Ga
6
S
16
is also a
promising IR NLO crystal. It is worth noting that the excellent NLO
properties of LaMg
6
Ga
6
S
16
can, to some extent, be attributed to the
particular contribution of La2+ cations. Since rare-earth La2+ cation can
exhibit similar polarizability with the transition Ag+and Zn2+ cations
and comparable electropositivity with the alkali and alkaline-earth
cations, LaMg
6
Ga
6
S
16
can combine the advantages of large SHG
responses of transition-cations chalcogenides and large band gaps of
alkali and alkaline-earth chalcogenides and achieve a better balance
between large SHG response and wide band gap.
Theoretical analysis
To better understand the structure–performance relationship, the
electronic structures of LaMg
6
Ga
6
S
16
were calculated by the first-
principles calculations. The calculated electronic bandstructure shows
that LaMg
6
Ga
6
S
16
is an indirect bandgap compound with a band gap of
2.2 eV (Fig. 6a), which is smaller than the experimental value (3.0 eV)
due to the limitation of using a generalized gradient approximation as
the exchange- correlation functional67. Further, the partial densities of
states of LaMg
6
Ga
6
S
16
were analyzed (Fig. 6b). It can be found that the
tops of valence bands (VBs) are composed of S 3p,Mg2p, and La 5d
orbitals, and the La 5dorbitals possess the vital contribution to the top
of VBs. The bottom of the conduction bonds (CBs) region is mainly Ga
4s,Ga4p,Mg3s,Mg3p,La6s,La5d,andS3porbitals. These results
indicate that the 5delectronic states of the La atom have a crucial
effect on the band gap of the optical properties of LaMg
6
Ga
6
S
16
.In
(a) (b) (c)
300 330 360 390 420 450 480
10
20
30
40
50
60
70
80
90
100
Intensity (a.u.)
Temperature (K)
Peak 1
346 K
Peak 2
384 K
(d) (e) (f)
400 450 500 550 600
340
345
350
355
360
365
370
375
380
Emission wavelength (nm)
Excitation wavelength (nm)
5.0x10
4
1.0x10
5
1.5x10
5
2.0x10
5
2.5x10
5
3.0x10
5
3.5x10
5
4.0x10
5
400 450 500 550
600
0
1x103
2x103
3x103
4x103
5x103
300
310
320
330
340
350
360
370
370 420 470 520 570 620 670 720
0.0
2.0x10
4
4.0x10
4
6.0x10
4
8.0x10
4
1.0x10
5
PL Intehsity
Emission wavelength (nm)
LaMg
6
Ga
6
S
16
500 nm
360 nm
Excitation
FWHM
127 nm
0 1020304050
0.001
0.01
0.1
1
Intensity (a.u.)
Time (μs)
LaMg
6
Ga
6
S
16
Fitting curve
O
ex = 360 nm
O
em = 500 nm
W
ave
= 6.63 μs
Fig. 4 | Luminescence properties of LaMg
6
Ga
6
S
16
and CaMg
6
Ga
6
S
16
.Excitation-
dependent PL spectra of LaMg
6
Ga
6
S
16
at room temperature a, the black dashed
square indicates the ultrabroad emission range; PL emission spectra of
LaMg
6
Ga
6
S
16
under 360 nm excitation at the room temperature b; Fitted TL
spectrum of LaMg
6
Ga
6
S
16
, two Gaussian bands peaking at 346 K (yellow dashed
line) and 384 K (violet dashed line) c; Excitation-dependent PL spectra of
CaMg
6
Ga
6
S
16
at room temperature d; Schematic diagram of the 5d orbitals split of
La2+ driven by the octahedral crystal field in LaMg
6
Ga
6
S
16
e; Room-temperature PL
decay curves monitored at 500 nm and excited at 360 nm f.
Article https://doi.org/10.1038/s41467-024-47209-4
Nature Communications | (2024) 15:2959 5
Content courtesy of Springer Nature, terms of use apply. Rights reserved

addition, we also calculated SHG coefficients based on the electronic
structure by the first-principles calculations. Clearly, the calculated
SHG coefficients of LaMg
6
Ga
6
S
16
(d
11
= 12.27 pm/V and d
22
=4.00pm/V)
are greater than that of the AeMg
6
Ga
6
S
16
(Ae = Ca, Sr, Ba) (Supple-
mentary Table 6), suggesting divalent La make the partial contribution
to SHG response of LaMg
6
Ga
6
S
16
.
In summary, the chemically stable crystalline La(II)-chalcogenide,
LaMg
6
Ga
6
S
16
has been synthesized by constructing the strong [LaS
6
]
octahedra crystal field in the [Mg/Ga-S]
∞
framework structure. XPS,
XANES and EPR unequivocally identified the nature of the La2+ in
LaMg
6
Ga
6
S
16
. Meanwhile, DSC, in-situ variable-temperature powder
XRD and a series of solid-state reactions further illustrate its stability.
Benefiting from the unique electronic configurations of La2+,an
ultrabroad-band green emission at 500 nm with FWHM of 127nm was
discovered in LaMg
6
Ga
6
S
16
. In particular, compared with a few syn-
thesized divalent lanthanides organic complexes, the thermal stable
divalent lanthanides inorganic compounds are still rarely researched.
LaMg
6
Ga
6
S
16
may be able to provide some insights for the efficient
syntheses of other low oxidation state lanthanide compounds.
Methods
Materials
La (99.9%) was purchased from Aladdin Co.Ltd. (China),MgS (99.99%),
Ga
2
S
3
(99.9%) and S (99.9%) were purchased from Beijing Hawk
Fig. 5 | Optical properties of LaMg
6
Ga
6
S
16
.Particle size dependence of SHG
intensities of LaMg
6
Ga
6
S
16
(blue line) and AgGaS
2
(pink line) a, the error bars from
left to right correspond to sieved crystal particle size ranges: 54–75, 75–100,
100–125, 125–150, 150–180 and 180–250 μm; Thickness of LaMg
6
Ga
6
S
16
crystal,
inset: crystal for birefringencedetermination and its interferencecolor observedin
the cross-polarized light b;UV–vis–NIR diffuse reflectance spectrum (inset: band
gap of LaMg
6
Ga
6
S
16
is 3.0 eV) c, FTIR spectrum between 4000 and 500cm−1d,and
Raman spectrum between 1000 and 50 cm−1eof LaMg
6
Ga
6
S
16
; Well-balanced
nonlinear optical properties of LaMg
6
Ga
6
S
16
compared to AgGaS
2
f.
-5.0
-2.5
0.0
2.5
5.0
)Ve
( y
g
renE
L
2.2 eV
VB
max
CB
min
H
M
K
H
A
(a) (b)
-5.0 -2.5 0.0 2.5 5.0 7.5
0
1
2
3
Energy (eV)
La 6s
La 5d
0
4
8
12 Mg 3s
Mg 2p
0
5
10
15
)Ve/setaS( SOD
Ga 4s
Ga 4p
0
20
40
60
80 S 3s
S 3p
Fig. 6 | Theoretical calculation results of LaMg
6
Ga
6
S
16
.Calculated bandstructure aand theprojected density of stateswith the energyregion from −5.0eV to 7.5 eV bof
LaMg
6
Ga
6
S
16
.
Article https://doi.org/10.1038/s41467-024-47209-4
Nature Communications | (2024) 15:2959 6
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Science and Technology Co. Ltd. (China), and all the reagents were
used without further refinement.
Syntheses
For the preparation of LaMg
6
Ga
6
S
16
, reactants of La (0.2 mmol),
Ga
2
S
3
(0.6 mmol), MgS (1.2 mmol), S (0.3 mmol) were mixed and
respectively loaded into graphite crucible and then they are sealed
into the silica tube and flame-sealed under 10–3Toor. The tu bes were
placed in a temperature-controlled furnace with the following
heating process: firstly, heated to 773 K at a rate of 5 K/h and held
this temperature for 10 h, then heated to 1273 K at a rate of 5 K/h and
kept at that temperature for 100 h. Subsequently, the furnace was
slowly cooled down to 573 K at a rate of 5 K/h. N, N−dimethylfor-
mamide (DMF) solvent was chosen to wash the products. Finally,
many millimeter-level pale-yellow crystals of LaMg
6
Ga
6
S
16
was
obtained with yields of ∼80 %, and all of them are stable under air
and moisture conditions for at least 3 months. In addition, their
thermal behaviors were studied by a series of solid-state reactions
with the following process: their pure polycrystalline samples were
firstly loaded into graphite crucibles. Then the graphite crucibles
were put into silica tubes and flame-sealed under 10–3Toor. These
tubes were heated to 373 K in 10 h and kept at this temperature for
about 24 h. Subsequently, they were cooled to room temperature
and the mixture in the tube were thoroughly grinded and sealed
into silica tubes again. The silica tubes were further heated to a
higher temperature, 473 K in 10 h and kept the temperatures for
24 h. Repeating the above process with a 100 K higher calcined
temperature than the last reaction.
Structural refinement and crystal data
PXRD patterns were collected setting from the 2θrange 10–70° with a
step width size of 0.01° and a step time of 2 s on an automated SmartLab
3KW powder X-ray diffractometer using Cu-K
α
radiation (λ=1.54057Å)
radiation. The purity of compound LaMg
6
Ga
6
S
16
was verified by PXRD
with the results as shown in Supplementary Fig. 1. To study their thermal
behaviors, in-situ variable-temperature powder XRD data of
LaMg
6
Ga
6
S
16
was collected using an SmartLab 9KW X-ray diffractometer
(Supplementary Fig. 4a), meanwhile, a series of solid-state reactions with
different reaction temperatures (room temperature-1323 K) were also
conducted and shown in Supplementary Fig. 4b. The crystal structure of
LaMg
6
Ga
6
S
16
was determined by single-crystal XRD on a Bruker SMART
APEX III CCD diffractometer using Mo K
α
radiation (λ=0.71073Å) at
297(2) K and the data was integrated with the SAINT program. All cal-
culations were implemented with programs from the SHELXTL crystal-
lographic software package68. Their crystal structures were solved by
direct methods using SHELXS and refined with full-matrix least-squares
methods on F2with anisotropic thermal parameters for all atoms69.
Crystallographic data for the structure reported in this paper has been
deposited with the Cambridge Crystallographic Data Centre (CCDC),
under deposition number 2280420. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_r-
equest@ccdc.cam.ac.uk, or by contacting The Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK. Crystal
data and structure refinement parameters were given in Supplementary
Table 1. Some structural parameters including interatomic distances and
angles, final refined atomic positions and isotropic thermal parameters
are listed in Supplementary Table 2 and Supplementary Table 3,
respectively.
X-Ray photoelectron spectroscopy
The XPS (ESCALLAB250Xi, Thermo Scientific) using a monochromatized
Al K
α
source equipped with Ar ion sputteringwas used for depth profiling
measurements of ionic valence and composition, where the peak posi-
tions were calibrated using the C 1speak position (284.8 eV).
Energy-dispersive spectroscopy
Microprobe elemental analyses and the elemental distribution maps
were measured on a field-emission scanning electron microscope
(Quanta FEG 250) made by FEI.
Synchrotron X-ray absorption spectroscopy
The XAS measurements were carried out at the XAS Beamline at the
Australian Synchrotron in Melbourne, Australia using a set of liquid
nitrogen cooled Si (111) monochromator crystals. The electron beam
energy is 3.0GeV. With the associated beamline optics (Si-coated
collimating mirror and Rh-coated focusing mirror), the harmonic
content of the incident X-ray beam was negligible. Data was collected
by using transmission mode, and the energy was calibrated using a Co
foil. The beam size was about 1 × 1 mm. Note that a single XAS scan
took about 1 h.
Electron paramagnetic resonance spectroscopy
The EPR measurement was conducted on Bruker EMXplus-6/1 EPR
spectrometer with a 9.2 GHz magnetic field.
Thermal Analysis
The thermal behavior of LaMg
6
Ga
6
S
16
was performed using an HCT-4
analyzer (Beijing Henven Experimental). The sample of ∼10 mg was
sealed in the customized vacuum-sealed tiny silica tubes and heated
from 50 to 1300°C at a rate of 10°C/min. The measurements were
carried out in an atmosphere of flowing N
2
.
Photoluminescence spectroscopy
The PL spectra were measured in room temperature using a fluores-
cence spectrometer (FLS-980, Edinburgh, UK). A 450 W xenon arc
lamp was employed as a continuous excitation light source. The
FLS980 spectrometer was configured with Red PMT photomultiplier
with spectral coverage from 370 nm to 650 nm.
Thermoluminescence spectroscopy
The TL curve was collected by the TOSL-3DS measuring instr ument (PMT
detector) with a heating rate of 5 °C/s after pre-irradiation for 5 min.
Birefringence
The birefringence of LaMg
6
Ga
6
S
16
was measured based on a cross-
polarizing microscope method with plate-shaped crystals61.The
thickness of the used crystal is 22.4μmforLaMg
6
Ga
6
S
16
(Fig. 5b), and
the observed interference color is second-order yellow along [0_10]
plane ofthe crystal in the cross-polarizingmicroscope (Supplementary
Fig. 8). Based on the Michal-Levy chart, its retardation (Rvalue) is
about 920 nm. Acc ording to the equatio n R=Δn×d (where R,Δn,andd
represent retardation, birefringence, and thickness, respectively)60,62,
the birefringence of LaMg
6
Ga
6
S
16
can be calculated.
UV−vis−NIR diffuse reflectance
The UV−vis−NIR optical diffuse reflectance spectrum of LaMg
6
Ga
6
S
16
in the range of 300–2100 nm was measured on Shimadzu SolidSpec-
3700DUV with BaSO
4
as a reference. The band gap was estimated on
basis of the absorption spectra that was derived from the reflection
spectrum using the Kubelka-Munk formula70.
IR and Raman spectroscopy
The IR spectrum in the range of 4000–500 cm−1was recorded on a
Fourier transform IR spectrometer using Nicolet iS50 FT with ATR. The
Raman spectrum of LaMg
6
Ga
6
S
16
in the range of 1000–50 cm−1was
recorded on WITec alpha300R. The characteristic vibrations in the
Raman spectrum at 424, 354, and 310 cm−1correspond to asymmetric
and symmetric stretching vibrations of S-Ga-S and S-Mg-S modes, and
peaks below 200 cm−1are due to the La-S and Mg-S vibrations. These
Article https://doi.org/10.1038/s41467-024-47209-4
Nature Communications | (2024) 15:2959 7
Content courtesy of Springer Nature, terms of use apply. Rights reserved

coincide with those of other related chalcogenides, such as
LaCaGa
3
S
6
OandAeMg
6
Ga
6
S
16
(Ae = Ca, Sr, Ba)27,71.
Second harmonic generation measurement
The SHG signals of LaMg
6
Ga
6
S
16
and benchmark AgGaS
2
were
investigated under incident laser radiation of 2090 nm by modified
Kurtz-Perry method, respectively72.SamplesLaMg
6
Ga
6
S
16
and
AgGaS
2
were sieved into several distinct particle size ranges
(54–75, 75–100, 100–125, 125–150, 150–180 and 180–250 μm) for
the PM measurements. The SHG signals were detected by a charge-
coupled device. The second harmonic efficiency of the
LaMg
6
Ga
6
S
16
powder was compared to that of AgGaS
2
powder with
the same particle size.
Laser-induced damage threshold measurement
The LIDTs of the LaMg
6
Ga
6
S
16
and AgGaS
2
powder at the particle size
range of 100 −125 μm were evaluated under using a high-power laser
irradiation of 1064 nm (pulse width τ
p
=10ns) by the single-pulse
method73,74. The measurement processes were performed by gradually
increasing the laser power until the damaged spot was observed under
a microscope. The damage thresholds were derived from the equation
I
(threshold)
=E/(πr2τ
p
),whereEis the laser energy of a single pulse, ris the
spot radius, and τ
p
is the pulse width.
Computational methods
The electronic band structures, the partial density of states and
optical properties for LaMg
6
Ga
6
S
16
were carried out using the
CASTEP package based on density functional theory (DFT)75. Gen-
eralized gradient approximation (GGA) parametrized by
Perdew–Burke–Ernzerhof (PBE) functional was chosen for the
exchange-correlation energy, and the pseudopotential was set as
norm-conserving pseudopotential (NCP)76. The valence electrons
were set as: La 6s25d1,Mg2s22p63s2,Ga3d104s24p1,S3s23p4for
LaMg
6
Ga
6
S
16
. The plane-wave energy cutoff value was set at
800.0 eV. The numerical integration of the Brillouin zone was per-
formed using 2 × 2 × 4 Monkhorst-Pack κ-point meshes77. The local-
density approximation (LDA) + U approach (where U is the Hubbard
energy) was adopted to deal with the strong on-site Coulomb
repulsion amongst the localized La 5delectrons78–80.
The SHG coefficients were calculated from the band wave func-
tions using the so-called length-gauge formalism derived by Aversa
and Sipe at a zero-frequency limit. The static second-order nonlinear
susceptibilities χ
αβγ
(2) can be reduced as81–83:
χαβγ
ð2Þ=χαβγ
ð2ÞVEðÞ+χαβγ
ð2ÞVHðÞ,ð3Þ
Virtual-Hole (VH), Virtual-Electron (VE) and Two-Band (TB) pro-
cesses play an important role in the total SHG coefficient χ(2).TheTB
process can be neglected owing to little contribution for SHG. The
formulas for calculating χ
αβγ
(2) (VE) and χ
αβγ
(2) (VH) are as follows:
χαβγ
ð2ÞðVEÞ=e3
2_2m3X
vcc0Zd3k
4π3pαβγðÞIm½Pα
vcPβ
cc0Pγ
c0v1
ω3
cvω2
vc0
+2
ω4
vcωc0v

,ð4Þ
χαβγ
ð2ÞðVHÞ=e3
2_2m3X
vv0cZd3k
4π3pαβγðÞIm½Pα
vv0Pβ
v0cPγ
cv1
ω3
cvω2
v0c
+2
ω4
vcωcv0

,
ð5Þ
Here, α,β,γare Cartesian components, vand v0denote valence
bands, cand c0refer to conduction bands, and P(αβγ)denotes the full
permutation. The band energy difference and momentum matrix
elements are denoted as ℏω
ij
and P
ij
α, respectively. As we know, the
virtualelectron (VE) progresses of occupied and unoccupied states are
the main contribution to the overall SHG effect84.
Data availability
The representative data and extended datasets that support the find-
ings of this study are available within the paper and its Supplementary
Information files. Additional data are available fromthe corresponding
author. The source data for Figs. 1,3a–c, 4a–d, f, 5a, c–f, 6a, b and
Supplementary Figs. 1, 3, 4a, 4b, 6, 8 are provided as a Source Data file.
The X-ray crystallographic coordinates for structure reported in this
study have been deposited at the Cambridge Crystall graphic Data
Center (CCDC), under deposition number 2280420. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/data_request/cif.Sourcedataare
provided with this paper.
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Acknowledgements
This work is supported by the National Natural Science Foundation of
China (Grant Nos. 52322202 (H. Y.), 52172006 (H. W.), 22071179 (H. Y.),
51972230 (H. W.), 51890864 (Y. W.), 51890865 (Z. H.), Natural Science
Foundation of Tianjin (Grant Nos. 20JCJQJC00060 (H. Y.) and
21JCJQJC00090 (H. W.), Tianjin University of Technology Research
Innovation Project for Postgraduate Students (YJ2234 (Y. Z.)).
Author contributions
Y.Z. performed the experiments, data analysis, and paper writing. J.C.
andK.L.performedtheexperiments.H.W.designedandsupervisedthe
experiments. H.Y. provided major revisions of the manuscript. Z.H.
supervisedthe optical experiments. J.W. and Y.W. helped the analysesof
the crystallization process and the data. All the authors discussed the
results and commented on the manuscript.
Competing interests
The authors declare no competing interest.
Additional information
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