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Using a kinetic model to fit time-resolved spectra a, Kinetic model of triplet energy transfer and decay, including the energy barrier to triplet transfer due to the heterogeneity of the bandgaps of Si NCs. b, Fits (red dashed line) to time-dependent populations of 9EA triplet excitons (blue solid line) and excited Si NCs (grey solid line) that faithfully reproduce the kinetics over five decades in time. We note that there is some discrepancy between the triplet population and the fit at short time delays, which is an artefact of the background normalization used to extract this population. c, The model in a reproduces the energy-dependent quenching of Si NC populations after functionalization with 9EA (red dashed line, model; solid lines, experiment).
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Inorganic semiconductor nanocrystals interfaced with spin-triplet exciton-accepting organic molecules have emerged as promising materials for converting incoherent long-wavelength light into the visible range. However, these materials to date have made exclusive use of nanocrystals containing toxic elements, precluding their use in biological or en...
Citations
... Annihilation can be defined as a transition between two excited states by a transfer of energy [11]. Energy transfer occurs not only between a donor (in an excited state) and an acceptor (in the ground state) [12,13,14,15]. But transitions between two excited states (an excited donor and an excited acceptor) can also occur, resulting in a donor with higher energy levels and an acceptor with a lower excited state or an acceptor in the ground state. ...
In this article, with a view to improving the efficiency of photovoltaic cells, and given the promising yields of silicon heterojunction photovoltaic cells, we have, using a silicon heterojunction cell (a-Si:H/c-Si) doped with (n+p) , studied the contribution of excitons to the internal quantum efficiency of charge carriers. We then developed a detailed explanation of the energy conversion phenomena, based on an exciton-exciton annihilation process, which allows the electrons of quasiparticles to retain some of their energy. We used a numerical method for solving the charge carrier transport equations and carried out some additional calculations, which enabled us to obtain some results. These results then enabled us to study the influence of the annihilation lifetime on the charge carrier photo-current density, leading to internal charge carrier quantum yields of between 29.29768% and 77.8525%.
... On the other hand, the evident absorption features by the anthracene groups in the samples of EEA-SiNCs and EE-SiNCs suggest the anthracene-containing ligands have successfully linked with surface Si atoms. 33 We next compared the potential influence on the PL features of SiNCs by surface functionalization approaches. Prior to ligand passivation, no PL was observed from H-SiNCs, possibly due to abundant surface traps or potential particle aggregation quenching PL, a commonly observed phenomenon that also has been reported. ...
... As for EE-and EEA-capped SiNCs, a new absorption signal at 370 nm emerged in the TA spectra (Figures 6and 7) and can be assigned to the triplet state of the surface anthracene groups. 33 Global analysis of the spectra in the UV−vis range confirms the presence of a time scale below 2 ns (1.94 and 1.03 ns for EEA-and EE-SiNCs, respectively), consistent with the time scale of energy transfer from the SiNC core to the triplet state of the surface anthracene groups. 33 The TA results in the NIR range, in contrast, only show one signal at 1050 nm (i.e., 1.18 eV, Figures 6 and 7), which can be interpreted with two compartments with time scales of 7.21 and 1.93 ns using global analysis (Figure 7). ...
... 33 Global analysis of the spectra in the UV−vis range confirms the presence of a time scale below 2 ns (1.94 and 1.03 ns for EEA-and EE-SiNCs, respectively), consistent with the time scale of energy transfer from the SiNC core to the triplet state of the surface anthracene groups. 33 The TA results in the NIR range, in contrast, only show one signal at 1050 nm (i.e., 1.18 eV, Figures 6 and 7), which can be interpreted with two compartments with time scales of 7.21 and 1.93 ns using global analysis (Figure 7). Notably, similar TA results in the NIR range and the kinetic compartments are found in the molecules of EEA and EE (Figures S13 and S14) and can be ascribed to the S 1 → S n conversion of the surface anthracene molecules. ...
Colloidal silicon nanocrystals (SiNCs) exhibit promise for applications in optoelectronics and bionanotechnology, attributed to their distinct surface-tunable photo-luminescence (PL) and photophysical characteristics. Alkoxylation has aroused interest as a functionalization methodology for the efficient construction of Si−O bonds on the surfaces of SiNCs under mild conditions. However, there exist different opinions on the influence of surface alkoxylation on the photophysical properties of colloidal SiNCs. Herein, we conduct a systematic comparison between hydrosilylation and alkoxylation on SiNC surfaces to explore the impact of alkoxyl-based ligands on the photophysical properties of SiNCs. The alkoxylated SiNCs exhibit a similar particle size and efficient surface ligand modification compared with their hydrosilylated counterparts. Consistent steady-state spectra and transient absorption results indicate that alkoxyl-passivated SiNCs do not change the SiNC-core-related electron−hole recombination dynamics or charge transfer between the SiNC core and the surface-modified ligands compared with the conventional alkyl-functionalized particles. We further demonstrated the application of alkoxylation to the functionalization of SiNCs with ligands that cannot be easily anchored on surfaces via conventional hydrosilylation approaches.
... The triplet sensitizer and annihilator are the essential components for TTA-UC, and a diagram illustrating the mechanism of TTA-UC is shown in Figure S1, in which the triplet-triplet energy transfer (TTET) process from the sensitizer to the annihilator and triplet-triplet annihilation (TTA) between the triplet annihilators are two pivotal processes for TTA-UC, both of which follow a Dexter mechanism. To facilitate the TTET process, photophysical properties of sensitizers [18][19][20] are optimized by either enhancing the visible-light absorption ability and/or extending the lifetime of their triplet states, and abundant sensitizers ranging from transition-metal complexes to metallic porphyrins and surface-engineered semiconductor nanocrystals were developed for TTA-UC [21][22][23][24]. Moreover, strategies for supramolecular pre-assembling of the sensitizers and annihilators in close proximity were also developed to facilitate the TTET process by allowing the TTET event to proceed in an intramolecular fashion instead of an intermolecular one [25][26][27][28][29]. ...
The triplet annihilator is a critical component for triplet–triplet annihilation upconversion (TTA-UC); both the photophysical properties of the annihilator and the intermolecular orientation have pivotal effects on the overall efficiency of TTA-UC. Herein, we synthesized two supramolecular annihilators A-1 and A-2 by grafting 9,10-diphenylanthracene (DPA) fragments, which have been widely used as triplet annihilators for TTA-UC, on a macrocyclic host—pillar[5]arenes. In A-1, the orientation of the two DPA units was random, while, in A-2, the two DPA units were pushed to a parallel arrangement by intramolecular hydrogen-bonding interactions. The two compounds showed very similar photophysical properties and host–guest binding affinities toward electron-deficient guests, but showed totally different TTA-UC emissions. The UC quantum yield of A-2 could be optimized to 13.7% when an alkyl ammonia chain-attaching sensitizer S-2 was used, while, for A-1, only 5.1% was achieved. Destroying the hydrogen-bonding interactions by adding MeOH to A-2 significantly decreased the UC emissions, demonstrating that the parallel orientations of the two DPA units contributed greatly to the TTA-UC emissions. These results should be beneficial for annihilator designs and provide a new promising strategy for enhancing TTA-UC emissions.
... 63,64 In the solution system composed of Si:9EA and DPA (Si:9EA/DPA), UC from 488-640 nm excitation light to 425 nm fluorescence was achieved with a maximum ΦUC of 3.5% (ΦUC' = 7%). 65 The Ith was estimated to be 0.95 Wcm −2 for 488 nm excitation and 2 Wcm −2 for 532 nm excitation, and this difference in Ith is attributed to the larger absorption cross-section of silicon nanoparticles in the shortwavelength region (Equation 9). 65 When the size of silicon nanoparticles decreased from 3.6 to 3.1 nm, ΦUC increased from 0 to 3.5 ± 0.5% (ΦUC' = 7.0 ± 0.9%). ...
... 65 The Ith was estimated to be 0.95 Wcm −2 for 488 nm excitation and 2 Wcm −2 for 532 nm excitation, and this difference in Ith is attributed to the larger absorption cross-section of silicon nanoparticles in the shortwavelength region (Equation 9). 65 When the size of silicon nanoparticles decreased from 3.6 to 3.1 nm, ΦUC increased from 0 to 3.5 ± 0.5% (ΦUC' = 7.0 ± 0.9%). This occurs because the bandgap increases as the nanoparticle size decreases. ...
... Overcoming these non-uniformity and instability issues may enable TET up to 91% in silicon nanoparticles. 65 The same research group has recently adopted a novel approach to enhance TET efficiency. 66 Specifically, they modified the binding mode of the anthracene-derived transmitter on the surfaces of silicon nanoparticles from C−C single bonds (Si:9EA) to C=C double bonds (Si:9VA, 9VA = 9vinylanthracene). ...
The phenomenon of photon upconversion (UC), generating high-energy photons from low-energy photons, has attracted significant attention. In particular, triplet-triplet annihilation-based UC (TTA-UC) has been achieved by combining the excitation states...
... Other studies have utilized digital delay generators to control the time delay between pulses. 117 New approaches have also applied asynchronous optical sampling techniques, in which two laser sources produce pump and probe pulses with different repetition rates to generate a periodically changing temporal delay. 118 The latter methodology has the advantage that long delay times up to tens of nanoseconds can be accomplished by simply adjusting the laser repetition rates. ...
... Based on amplified 1−10 kHz lasers, numerous investigations have been performed on the electronic and acoustic ultrafast dynamics of various nanomaterials and photosynthetic structures in solution through TA spectroscopy. 117,154−160 The low repetition rates make it possible to monitor slow dynamics without the build-up of long-lived excited species, and also enable multichannel detection to measure the absorption signal on a shot-to-shot basis. The tradeoff is that only limited spatial information is possible, and the maximum differential signals do not generally exceed 10 −5 . ...
Ultrafast optical microscopy, generally employed by incorporating ultrafast laser pulses into microscopes, can provide spatially resolved mechanistic insight into scientific problems ranging from hot carrier dynamics to biological imaging. This Review discusses the progress in different ultrafast microscopy techniques, with a focus on transient absorption and two-dimensional microscopy. We review the underlying principles of these techniques and discuss their respective advantages and applicability to different scientific questions. We also examine in detail how instrument parameters such as sensitivity, laser power, and temporal and spatial resolution must be addressed. Finally, we comment on future developments and emerging opportunities in the field of ultrafast microscopy.
... In the spectrum of Si:9EA (Fig. 1, blue), a series of resonances appear at 396, 375 and 356 nm that correspond to the vibrational fine structure of the S 0 → S 1 transition of 9-ethylanthracene (9EA) molecules bound to silicon. As noted in prior work 28 , these resonances are slightly redshifted relative to corresponding features in the absorption spectrum of 9-methylanthracene (9MA; Fig. 1, inset), but otherwise do not differ in their linewidth or oscillator strength, indicating that the electronic coupling between 9EA molecules and the silicon QDs to which they are bound is weak. ...
... Figure 2b plots emission spectra obtained from toluene solutions containing Si:9VA and one of two known emitters, 9,10-diphenylanthacene (DPA) or 2,5,8,11-tetra-tert-butylperylene (tBu 4 P). Previously, we showed Si:9EA can efficiently drive triplet exciton transfer to DPA, fuelling production of upconverted light with 7% efficiency 28 . We note the in-flight functionalized Si QDs we employ for this work have allowed us to improve that yield to 15.8%. ...
... This enhanced coupling impacts both the energy and spatial distribution of spin-triplet excitons formed by this system, as evidenced by measurable effects in steady-state and time-resolved optical experiments, as well as in electronic structure calculations that all differ qualitatively from those of systems lacking strong coupling. By varying the energy of strongly coupled triplet excitons via altering the number of anthracene molecules that couple to silicon QDs, we design a photon upconversion system that converts green light to blue, achieving an efficiency (17.2%) and threshold power (0.5 W cm -2 ) that surpass values obtained for prior silicon-QD-based systems 28 . This system's efficiency also compares favourably with the best values achieved to date for QD-based upconversion systems 1 . ...
Hybrid structures formed between organic molecules and inorganic quantum dots can accomplish unique photophysical transformations by taking advantage of their disparate properties. The electronic coupling between these materials is typically weak, leading photoexcited charge carriers to spatially localize to the dot or to a molecule at its surface. However, we show that by converting a chemical linker that covalently binds anthracene molecules to silicon quantum dots from a carbon–carbon single bond to a double bond, we access a strong coupling regime where excited carriers spatially delocalize across both anthracene and silicon. By pushing the system to delocalize, we design a photon upconversion system with a higher efficiency (17.2%) and lower threshold intensity (0.5 W cm–2) than that of a corresponding weakly coupled system. Our results show that strong coupling between molecules and nanostructures achieved through targeted linking chemistry provides a complementary route for tailoring properties in materials for light-driven applications.
... 124,125 Singlet oxygen ( 1 O 2 ) was indicated by strong PL spectra at l max 1270 nm. Xia et al. (2020) 126 demonstrated that conjugated 9-ethyl anthracene (9EA)-functionalized SiQDs carry out the TTA-UC mechanism when dispersed in 9,10-diphenyl anthracene (DPA) The experiment was conducted under an inert nitrogen atmosphere using (9-EA)-SiQDs as a sensitizer and DPA as an emitter. The efficient Dexter-energy transfer was investigated by femtosecond transient absorption spectroscopy. ...
... 124,125 Singlet oxygen ( 1 O 2 ) was indicated by strong PL spectra at l max 1270 nm. Xia et al. (2020) 126 demonstrated that conjugated 9-ethyl anthracene (9EA)-functionalized SiQDs carry out the TTA-UC mechanism when dispersed in 9,10-diphenyl anthracene (DPA) The experiment was conducted under an inert nitrogen atmosphere using (9-EA)-SiQDs as a sensitizer and DPA as an emitter. The efficient Dexter-energy transfer was investigated by femtosecond transient absorption spectroscopy. ...
... Authors described it as being due to reducing particle size, the bandgap energy laid above 9EA triplet state (B1.8 eV), and the energy barrier was reduced for nanocrystals to molecule energy transfer and led to increasing upconversion quantum yields. 126 One example of a TTA-UC mechanism illustrates in Fig. 12. ...
Silicon quantum dots (SiQDs) are of great interest because they are believed to be harmless to living organisms, mainly due to their low toxicity. They have great potential for various applications such as in optoelectronics, photonics, and photodynamic therapy. As the Si core is susceptible to oxidation, efforts are needed to protect the core or to passivate it. This passivation/functionalization is aimed at both the protection of the core and the enhancement of the light emission. The importance of surface modification of SiQDs concerning the effect of quantum confinement and ligand type on their photoluminescence quantum yield is discussed in this review. Different functionalization reactions are described along with the precursors used. Among these are hydrosilylation reactions between the silicon core and the carbon of alkyl ligands and chromophoric ligands. Alkyl ligands protect the silicon core and provide chemical and light stability to the silicon. Ligands containing chromophoric groups also play a role in increasing the absorption of light, which in turn can increase the emission of PL light. These chromophoric ligands can also be used for optoelectronic, photonic, energy conversion, and biological purposes to enhance photophysical properties through energy transfer mechanisms. The energy transfer between the SiQDs and the ligands allows the triplet–triplet annihilation to enhance the emission and the generation of singlet oxygen. Finally, a brief description is given of the opportunities that SiQDs can offer and the progress made in recent years in the potential applications of SiQDs. They can be used as materials for light-harvesting antennas, bioimaging, luminescent solar concentrators, LEDs, and photosensors by exploiting triplet–triplet annihilation and singlet oxygen.
... 107 Thus, we conclude that ultra-small AZTS NCs can sensitize red-to-blue triplet fusion upconversion, adding to the short list of solution-based upconversion facilitated by less-toxic NC sensitizers. 55,[108][109][110] Scheme 2. Cartoon of the proposed upconversion mechanism. Red light (λex.: 637 nm) is absorbed by AZTS NCs, and the energy from these photoexcitations is transferred to the spin-triplet state on surface-anchored 9-ACAligands. ...
... 3,13,[50][51]111 We extract Ith=3.1 W/cm 2 from the inflection point in our excitation-density-dependent measurements (Figure 6c), which is comparable to reported systems with less-toxic NC sensitizers. 55,[108][109][110] However, only one of these systems has generated photochemically-active deep-blue light (0-0 shoulder of DPA at λ: 415 nm) from red excitation (λ: 637 nm) 13 -thus achieving a beneficially larger anti-Stokes shift (Δ =1.04 eV) relative to yellow/green excitation (λ<590nm)-and our system breaks new ground with a threshold intensity more than 10x lower. Thus, our upconversion platform built on ultra-small AZTS NCs stands as a strong candidate among the rising tide of less-toxic NC-sensitized tripletfusion systems. ...
Pirquitasite Ag2ZnSnS4 (AZTS) nanocrystals (NCs) are emergent, lead-free emissive materials in the coinage chalcogenide family with applications in optoelectronic technologies. Like many multinary nanomaterials, their phase-pure synthesis is complicated by the generation of e.g. binary/ternary chalcogenide and metallic impurities. Here, we develop a stepwise synthetic procedure that controls the size, morphology, and transformations of acanthite (Ag2S) and canfieldite (Ag8SnS6) intermediates. This reaction scheme improves size-dispersity and grants the production of small AZTS NCs (d: 2.1-4.0 nm) that have not been achieved through established single-injection procedures expanding the accessible quantum-confined AZTS emission to shorter wavelengths (650-740 nm). We show that the initial sulfur stoichiometry is the key handle for template-size tunability and reveal that temporally separating transformation steps is crucial to obtaining <740 nm emitting AZTS NCs. We then use NMR and optical spectroscopies to demonstrate that the installation of thiol ligands improves colloidal stability and photoluminescence, while carboxylate ligands do not. Finally, facilitated by this enhanced synthetic control, we show that our AZTS NCs can act as effective and less-toxic sensitizers for red-to-blue triplet fusion upconversion. Our results highlight transferrable insights for the synthesis and post-synthetic treatment of complex less-toxic quaternary nanocrystalline systems.
... 107 Thus, we conclude that ultra-small AZTS NCs can sensitize red-to-blue triplet fusion upconversion, adding to the short list of solution-based upconversion facilitated by less-toxic NC sensitizers. 55,[108][109][110] Scheme 2. Cartoon of the proposed upconversion mechanism. Red light (λex.: 637 nm) is absorbed by AZTS NCs, and the energy from these photoexcitations is transferred to the spin-triplet state on surface-anchored 9-ACAligands. ...
... 3,13,[50][51]111 We extract Ith=3.1 W/cm 2 from the inflection point in our excitation-density-dependent measurements (Figure 6c), which is comparable to reported systems with less-toxic NC sensitizers. 55,[108][109][110] However, only one of these systems has generated photochemically-active deep-blue light (0-0 shoulder of DPA at λ: 415 nm) from red excitation (λ: 637 nm) 13 -thus achieving a beneficially larger anti-Stokes shift (Δ =1.04 eV) relative to yellow/green excitation (λ<590nm)-and our system breaks new ground with a threshold intensity more than 10x lower. Thus, our upconversion platform built on ultra-small AZTS NCs stands as a strong candidate among the rising tide of less-toxic NC-sensitized tripletfusion systems. ...
Pirquitasite Ag2ZnSnS4 (AZTS) nanocrystals (NCs) are emergent, lead-free emissive materials in the coinage chalcogenide family with applications in optoelectronic technologies. Like many multinary nanomaterials, their phase-pure synthesis is complicated by the generation of e.g. binary/ternary chalcogenide and metallic impurities. Here, we develop a stepwise synthetic procedure that controls the size, morphology, and transformations of acanthite (Ag2S) and canfieldite (Ag8SnS6) intermediates. This reaction scheme improves size-dispersity and grants the production of small AZTS NCs (d: 2.1-4.0 nm) that have not been achieved through established single-injection procedures expanding the accessible quantum-confined AZTS emission to shorter wavelengths (650-740 nm). We show that the initial sulfur stoichiometry is the key handle for template-size tunability and reveal that temporally separating transformation steps is crucial to obtaining <740 nm emitting AZTS NCs. We then use NMR and optical spectroscopies to demonstrate that the installation of thiol ligands improves colloidal stability and photoluminescence, while carboxylate ligands do not. Finally, facilitated by this enhanced synthetic control, we show that our ultra-small AZTS NCs can act as effective and less-toxic sensitizers for red-to-blue triplet fusion upconversion. Our results highlight transferrable insights for the synthesis and post-synthetic treatment of complex less-toxic quaternary nanocrystalline systems.
... While initial studies focused on conventional nanocrystals such as PbS and CdSe, more recently, less conventional nanocrystals including perovskite NCs, [15][16][17][18] ternary quantum dots 18 or Si nanocrystals have also been introduced. 19 Depending on the specific system investigated, the spin-triplet states were generated either by a Dexter-type bound triplet energy transfer or a two-step charge transfer process. [20][21][22][23] For detailed reviews on photon UC, we refer the readers to the following review articles. ...
Perovskite-sensitized triplet-triplet annihilation (TTA) upconversion (UC) holds potential for practical applications of solid-state UC ranging from photovoltaics to sensing and imaging technologies. As the triplet sensitizer, the underlying perovskite properties heavily influence the generation of spin-triplet states once interfaced with the organic annihilator molecule, typically polyacene derivatives. Presently, most reported perovskite TTA-UC systems have utilized rubrene doped with ∼1% dibenzotetraphenylperiflanthene (RubDBP) as the annihilator/emitter species. However, practical applications require a larger apparent anti-Stokes than is currently achievable with this system due to the inherent 0.4 eV energy loss during triplet generation. In this minireview, we present the current understanding of the triplet sensitization process at the perovskite/organic semiconductor interface and introduce additional promising annihilators based on anthracene derivatives into the discussion of future directions in perovskite-sensitized TTA-UC.
