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Cd 81 Mn 1 Se 82 quantum dot where an Mn atom (purple) is placed (a) in the middle and (b) at the surface of a QD.
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In this work, we study the effect of a dual luminescence for CdSe quantum dots (QDs) doped by a manganese impurity. In this effect, one line has fast relaxation and corresponds to light emission from CdSe conduction band, whereas the second is very slow in relaxation with the relaxation time of 0.1–1.0 ms. The second line disappears for quantum dot...
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... reality, the luminescence, nevertheless, takes place due to small spin−orbit interaction as mentioned in refs 43,56−. In this work, we theoretically study both luminescence lines for an Mn impurity that is placed in the middle and also at the surface of a quantum dot, as shown in Figure 2a,b. The ligand field symmetries in both cases are different. ...
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We study the effect of manganese impurities on optical and magnetic properties of PbS quantum dots (QDs) of different sizes. We find that at low Mn concentrations, the manganese atoms slightly change the absorption spectra of pure PbS nanocrystals. A soon as the number of Mn atoms increases a QD energy gap expands. In a PbS QD there is a distinct e...
Citations
... Their PL can be tuned by reaction stoichiometry, temperature, and reaction time. 16,33 Exciton dynamics in NCs is complicated by hot electrons generated by above band gap excitation. The resultant Auger processes in doped NCs may be blocked by scavenging hot holes, giving rise to phonon bottleneck. ...
Brightly photoluminescent Cu-doped CdSe nanotetrapods (NTPs) have been prepared by a modified hot injection method. Their photoluminescence (PL) has a quantum yield of 38% and decays slowly over a few microseconds, while the PL in undoped NTPs has a rather small quantum yield of 1.7% and decays predominantly in tens of picoseconds, with a minor component in the nanosecond time regime. PL spectra of doped NTPs are significantly Stokes shifted compared to the band edge (BE). Efficient PL quenching by a hole scavenger confirms the oxidation state of +I for the dopant ion and establishes hole capture by this ion to be the primary event that leads to the Stokes shifted PL. A fast decay of the photoinduced absorption band, along with a similar decay in PL, observed in a femtosecond optical gating experiment, yields a time constant of about a picosecond for the hole capture from the valence band (VB) by Cu+. The remarkably long PL lifetime in the doped NTPs is ascribed to the decrease in the overlap between the wavefunctions of the photogenerated electrons and the captured hole. Hot carrier relaxation processes, triggered by excitation at energies greater than the band gap, leave their signature in a rise time of few hundreds of femtoseconds, in the ground state bleach recovery kinetics. Hence, a complete picture of exciton dynamics in the doped NTPs has been obtained using ultrafast spectroscopic techniques working in tandem.
... In general, as the sizes of metal and semiconductors gradually decrease to nanometer scale, their optical performance is increasingly dependent on their sizes and shapes, and largely different from the properties of bulk materials and atomic molecules [2]. CdSe QDs have many unique optoelectronic properties [3], which include size-tunable photoluminescence (PL), the narrowband of emission, bright photoluminescence, and lengthened optical absorption in the UV-vis region [4][5][6]. Its nonlinear optical performance is also receiving more and more attention [7,8]. ...
Through the process of magnetron sputtering and spin-coating, CdSe/Al2O3/Ag and CdSe/PMMA/Ag composite films were fabricated. All the composite films' linear optical performances, morphology and structure have been concluded. Composite films' nonlinear refraction and absorption properties were investigated by fs Z-scan technique. When the laser energy is increased from 100nj to 500nj, the CdSe/PMMA/Ag composite films' saturated absorption (SA) are enhanced, and the CdSe/Al2O3/Ag composite films are converted from SA to reverse saturated absorption (RSA), the nonlinear absorption behavior can be explained by a three-level model. At 300nj laser energy, all the composite films exhibit SA. Both the composite films' nonlinear refraction and absorption were enhanced with the increasing of Ag nanoparticles (NPs) sputtering power. However, with the layers of CdSe quantum dots (QDs) increasing, the composite films' nonlinear absorption and refractive indexes were both decreased. Moreover, the CdSe/PMMA/Ag composite films’ third-order nonlinear polarization index, as compared with that of the CdSe/Al2O3/Ag composite films, are about ten times higher. Composite films can be used in many types of signal processing as well as in photonics and optoelectronic applications.
... From the absorption profiles and the values presented, besides the near gap excitations, these nanoparticles (based on Mg or Al) exhibit maximum oscillator strengths (throughout the uv/vis region) that is comparable to other systems, even of larger sizes [45][46][47], such as the QDs discussed in the Introduction section. In almost all cases the oscillator strengths increase significantly at higher excitation energies. ...
The electronic and optical properties of magnesium and aluminum hydride nanoparticles (NPs) have been examined using density functional theory (DFT) and time dependent DFT (TD-DFT). The absorption spectra (AS) of small size NPs obtained from selected functionals have been compared with high accuracy results from the equation-of-motion coupled-cluster with single and double excitations (EOM-CCSD) method. The comparison showed that the ASs from the CAM-B3LYP functional were in closer agreement with EOM-CCSD results. All calculations for NPs of larger sizes were performed using CAM-B3LYP. We show that the optical gap varies from 0.2 up to 5.5 eV for Mg n H m , and from 1.0 up to 7 eV for Al n H m . The variation of the OG depends on two factors: the number of electrons in each NP (NP S with even number of electrons have higher OG), and the number of hydrogen atoms with the fully hydrogenated NPs (Mg n H 2n and Al n H 3n ) having the highest OGs. That type of NPs show promise for applications such as quantum dots, e.g. solar cells, light emitting diodes and biolabeling.
... 1,2 Much research has been done on II-VI and III-V DMSs, especially semiconductors doped by transition metal (TM) impurities where many unusual magnetic and optical properties have been observed in their nanocrystals. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Because of the importance of ferromagnetism at room temperature for various applications in DMSs, much research has been focused on investigating DMS materials that satisfy this criterion. Different types of dopants can substantially change the value of a magnetic moment in metal-oxide nanocrystals. ...
Because of the importance of ferromagnetism at room temperatures we quest for new materials that can exhibit a non-vanishing magnetic moment at room temperatures and at the same time can be used in spintronics. The experimental results indicate that d⁰ ferromagnetism without any magnetic impurities takes place in PbS films made of lead sulfide 30 nm close-packed nanoparticles. To explain the existence of the d⁰ ferromagnetism we propose a model where various Pb bulk and surface vacancy configurations are analyzed. The bulk configuration have zero magnetic moments while the two surface configurations with the same non-vanishing magnetic moments and the lowest ground state energies contribute to the total magnetization. Based on the experimental value of the saturation magnetization, 0.2 emu/g, we have found that the calculated Pb vacancy concentration should be about 3.5 % that is close to typical experimental values. Besides very important important for applications, there is one feature of PbS d⁰ ferromagnetism that makes this material special for fundamental research. PbS ferromagnetism can exhibit topologically driven spacial magnetic moment distributions (e.g., magnetic skyrmions) because of the large spin-orbit coupling.
... 27 Mn 2+ -doped CdSe has been investigated using density functional theory (DFT), timedependent DFT (TDDFT), and configuration interaction singles methods to show the band alignment of the NC/QD relative to the dopant influencing PL properties. 28 Role of passivation ligands on equilibrium geometry and optical properties of magic-sized CdSe clusters has been studied. 29 Modeling of optical transitions in Mn 2+ -doped ZnO QDs has also been studied. ...
Fully inorganic lead halide perovskite nanocrystals (NCs) are of interest for optoelectronic and light-emitting devices because of their photoluminescence (PL) emission properties, which can be tuned/optimized by (I) surface passivation and (II) doping. (I) Surface passivation of the NC affects PL capabilities, as an underpassivated surface can introduce trap states, which reduces PL quantum yields. (II) Doping NCs and quantum dots with transition-metal ions provides stable optical transitions. Doping perovskite NCs with Mn²⁺ ions provides high-intensity ⁴T1 → ⁶A1 optical transitions in addition to the bright intrinsic NC emission. Here, we use noncollinear density functional theory (DFT) to investigate the roles of surface passivation and doping on the PL emission stability of perovskite NCs. Two models are investigated: (i) a pristine NC and (ii) a NC doped with the Mn²⁺ ion. The noncollinear DFT includes spin-orbit coupling (SOC) between different spin states and produces spin adiabatic molecular orbitals. These orbitals are used to calculate the transition dipoles between electronic states, oscillator strengths, radiative transition rates, and emission spectra. It was found that the noncollinear spin basis with SOC slows down hole relaxation in the doped NC by 2 orders of magnitude compared to spin-polarized basis. This is attributed to "spin-flip" transition from the perovskite NC to the Mn²⁺ dopant and low-probability nonradiative d-d transition.
... Cadmium selenide (CdSe), a well-known direct band gap II-VI semiconductor, favours absorption over a wide range of the visible spectrum. Because of high luminescence efficiency and easily adjustable luminescence [1] from ultraviolet to near infrared region, it has been a promising material for application in various upcoming fields based on photodetectors, memory devices, solar cells [2], Light-emitting diodes (LEDs), biosensors, biomedical imaging as well as labeling [3]. There are numerous techniques to synthesize CdSe nanocomposite thin films as reported by various authors, viz. ...
Undoped and Mn/Cu/(Mn+Cu) doped CdSe colloidal quantum dots embedded in Starch matrix have been synthesized by adopting single-step chemical bath deposition method. X-ray diffraction (XRD) results show cubic zinc blende structures in both doped and undoped samples. The estimated particle sizes from the XRD are found to be in the range (6.9–10.3) nm. The HRTEM images exhibit irregular shaped nanoparticles with size in the range (6–10.2) nm. Thus, the particle sizes estimated from XRD results roughly agree with those from HRTEM measurements. The UV–Vis absorption spectra for both doped and undoped samples show blue shift, suggesting quantum confinement. All the undoped and doped samples show PL emission in the range 510–653 nm. PL intensity is found to increase due to doping. Two terminal electrochemical devices are fabricated with the as-prepared doped and undoped samples as the active layer with ITO coated glass slide and aluminum (Al) as electrodes. I–V characteristics of the as-fabricated devices exhibit pinched hysteresis loops having memristive, memcapacitive and meminductive nature. A new parameter is conceptualized which is found to be sensitive to doping material as well as doping concentration. Schottky emission mechanism is found to be dominant in both low resistance state and high resistance state. ON/OFF switching features favour Coulomb Blockade phenomenon.
... Compared to the PLE spectrum of SiNCs (Supporting Information,Figure S8), which decreases monotonically in intensity from 300 nm to approximately 480 nm, the PLE spectra of doped SiNCs feature a weak but distinct band centered around 365 nm. This band is seen in the PLE spectra of all doped SiNCs, irrespective of the dopant and the NC growth temperature; although the overall band patterns of the PLE spectra vary depending on the dopants.[6,18,22]The PL decay of metal-doped SiNCs follows a bi-exponential profile (Supporting Information,Figure S9). ...
Impurity-doping in nanocrystals significantly affects their electronic properties and diversifies their applications. Herein, we report the synthesis of transition metal (Mn, Ni, Co, Cu)-doped oleophilic silicon nanocrystals (SiNCs) through hydrolysis/polymerization of triethoxysilane with acidic aqueous metal salt solutions, followed by thermal disproportionation of the resulting gel into a doped-Si/SiO2 composite that, upon HF etching and hydrosilylation with 1-n-octadecene, produces free-standing octadecyl-capped doped SiNCs (diameter?3 to 8?nm; dopant <0.2 atom %). Metal-doping triggers a red-shift of the SiNC photoluminescence (PL) of up to 270?nm, while maintaining high PL quantum yield (26?% for Co doping).
... This band is seen in the PLE spectra of all doped SiNCs, irrespective of the dopant and the NC growth temperature; although the overall band patterns of the PLE spectra vary depending on the dopants. [6,18,22] The PL decay of metal-doped SiNCs follows a bi-exponential profile (Supporting Information, Figure S9). The decay is slower than that of SiNCs, in which the slow component of the decay has a lifetime of circa 515 ms. ...
Impurity-doping in nanocrystals significantly affects their electronic properties and diversifies their applications. Herein, we report the synthesis of transition metal (Mn, Ni, Co, Cu)-doped oleophilic silicon nanocrystals (SiNCs) through hydrolysis/polymerization of triethoxysilane with acidic aqueous metal salt solutions, followed by thermal disproportionation of the resulting gel into a doped-Si/SiO2 composite that, upon HF etching and hydrosilylation with 1-n-octadecene, produces free-standing octadecyl-capped doped SiNCs (diameter≈3 to 8 nm; dopant <0.2 atom %). Metal-doping triggers a red-shift of the SiNC photoluminescence (PL) of up to 270 nm, while maintaining high PL quantum yield (26 % for Co doping).
... Therefore, the structural and the electronic properties of Cd n S n (n ¼ 1-8) clusters have been studied by using DFT methods. 37 It established that the lower impurity concentration has an insignicant impact on the band gap of QDs, 38 and also the presence of impurity on the surface of a QD due to its large surface to volume ratio can drastically change the band gap. Therefore, a theoretical understanding of the dopant's interaction in doped CdS clusters especially the dopant at the surface may shed light in improving the optical properties for the desired photovoltaic applications. ...
The influence of doping metal ions on the structural, electronic and optical properties of Cdn-yXySn (n = 6, 15; y = 1, 2, 4) clusters is systematically studied using DFT and TD-DFT studies. Among the dopants, Cu2+ and In2+ slightly distort the structure of CdnSn clusters, though they have the strong bonding interaction with S2- however; other two dopants In2+, Hg2+ significantly distort the cluster's structure. Molecular composition analysis reveals the dopants not only contribute to the optically active states, but also for the surface or trap states. The HOMO-LUMO gap is significantly reduced for Cu2+, Ga2+, and In2+ dopants. However, for Hg2+ the gap is meagerly affected. In large clusters Cd15S15, the polarizability values decrease on doping, though individual dopants show a nonlinear pattern. The absorption spectra of doped CdS clusters are generally red shifted though few Ga and In clusters exhibit blue shift nature due to Burstein-Moss effect.
... 20 Doping of semiconductor nanocrystals (NCs) by manganese atoms results in diluted magnetic semiconductors that can exhibit simultaneously both a magnetic order and unusual optical properties. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Such magnetic nanocrystals can be efficient in nanospintronics 38 and may become a novel class of emissive materials. 29 Mn doped ZnS quantum nanoscale materials exhibit ferromagnetism with Curie temperatures below or near room temperature. ...
Room temperature ferromagnetic
semiconductors have a great deal of advantage because of their easy integration into semiconductor devices. ZnS
nanocrystals (NCs), bulk, and surfaces exhibit d
0
ferromagnetism at room temperature. The experiments reveal that NC ferromagnetism takes place at low and room temperatures only due to Zn
vacancies (S vacancies do not contribute). To understand the mechanism of d
0
ferromagnetism, we introduce the surface-bulk model of a nanocrystal, which includes both surface and bulk magnetizations. The calculations demonstrate that the surface has the higher than bulk magnetization. We find the mechanism of the ferromagnetism is due to sulfur s- and p-electrons in a tetrahedral crystal field. The bulk magnetic moment increases with Zn
vacancy concentration at small concentrations and then goes down at larger concentrations. A surface
magnetic moment behaves differently with the concentration. It is always a monotonically rising function. We find that the total NC magnetic moment increases with the size and concentration of Zn
vacancies (only low concentrations). We also study the magnetization per unit cell where we find that it decreases for the surface and increases for bulk magnetism with the NC size.
