Exciton storage by Mn(2+) in colloidal Mn(2+)-doped CdSe quantum dots

Colloidal Mn (2+)-doped CdSe quantum dots showing long excitonic photoluminescence decay times of up to tau exc = 15 mus at temperatures over 100 K are described. These decay times exceed those of undoped CdSe quantum dots by approximately 10 (3) and are shown to arise from the creation of excitons by back energy transfer from excited Mn (2+) dopant ions. A kinetic model describing thermal equilibrium between Mn (2+ 4)T 1 and CdSe excitonic excited states reproduces the experimental observations and reveals that, for some quantum dots, excitons can emit with near unity probability despite being approximately 100 meV above the Mn (2+ 4)T 1 state. The effect of Mn (2+) doping on CdSe quantum dot luminescence at high temperatures is thus completely opposite from that at low temperatures described previously.     

Size-dependent electron transfer from PbSe quantum dots to SnO2 monitored by picosecond Terahertz spectroscopy

We report the direct and unambiguous determination of electron transfer rates and efficiencies from PbSe quantum dots (QDs) to mesoporous SnO2 films. We monitor the time-dependent electron density within the oxide with picosecond time resolution using Terahertz spectroscopy, following optical excitation of the QDs using a femtosecond laser pulse. QD-oxide electron transfer occurs with efficiencies of ～2% in our samples under 800 nm pumping with a marked dependence on QD size, ranging from ～100 ps injection times for the smallest, ～2 nm diameter QDs, to ～1 ns time scale for ～7 nm QDs. The size-dependent electron transfer rates are modeled within the framework of Marcus theory and the implications of the results for device design are discussed.     

Enhanced emissions of Eu(3+) by energy transfer from ZnO quantum dots embedded in SiO(2) glass

SiO(2):Eu(3+) based bulk composites containing ZnO quantum dots were synthesized by an in situ sol-gel process. The quantum dots homogeneously distributed among the SiO(2) glass matrix exhibited a broad ultraviolet emission band centered at 385?nm. The ZnO ultraviolet luminescence intensity decreased monotonically with increasing Eu(3+) doping concentration, while the Eu(3+) visible emission was intensified significantly by the precipitation of ZnO quantum dots, ascribed to the energy transfer from ZnO to Eu(3+). The Eu(3+) luminescence at 612?nm for the sample with 20?mol% ZnO was about ten times stronger than that for the sample without ZnO. The influence of ZnO or Eu(3+) concentration on the energy transfer process is discussed.     

Spin-polarizable excitonic luminescence in colloidal Mn2+-doped CdSe quantum dots

The photoluminescence of colloidal Mn2+-doped CdSe nanocrystals has been studied as a function of nanocrystal diameter. These nanocrystals are shown to be unique among colloidal doped semiconductor nanocrystals reported to date in that quantum confinement allows tuning of the CdSe bandgap energy across the Mn2+ excited-state energies. At small diameters, the nanocrystal photoluminescence is dominated by Mn 2+ emission. At large diameters, CdSe excitonic photoluminescence dominates. The latter scenario has allowed spin-polarized excitonic photoluminescence to be observed in colloidal doped semiconductor nanocrystals for the first time.     

钇或钕掺杂TiO_2纳米纤维的制备及光催化性能研究

采用静电纺丝技术,以Ti(SO4)2、聚乙烯吡咯烷酮(PVP,Mr=1300000)、稀土氧化物和N,N-二甲基甲酰胺(DMF)为原料,成功地制备了TiO2、Y/TiO2和Nd/TiO2纳米纤维.用XRD、FESEM、TEM和TG-DTA等分析手段对样品进行了表征.XRD分析结果表明,当焙烧温度为550℃时得到纯锐钛矿相RE/TiO2(RE=Y,Nd)纳米纤维,900℃时得到纯金红石型RE/TiO2(RE=Y,Nd)纳米纤维,稀土离子显著降低了TiO2的晶格参数.FESEM分析结果表明,RE/TiO2(RE=Y,Nd)纳米纤维直径约为50nm、长度300μm.以罗丹明B和苯酚为目标降解物,研究了三种催化剂的光催化性能.其中,1.5mol%Y/TiO2光催化剂对罗丹明B的降解效率较高,而1.0mol%Nd/TiO2对苯酚具有较好的降解活性.因此,掺杂不同稀土离子的TiO2纳米纤维对不同降解物的降解能力不同.     

Hole transport in organic field-effect transistors with active poly(3-hexylthiophene) layer containing CdSe quantum dots

Hybrid field-effect transistors (FETs) based on poly(3-hexylthiophene) (P3HT) containing CdSe quantum dots (QDs) were fabricated. The effect of the concentration of QDs on charge transport in the hybrid material was studied. The influence of the QDs capping ligand on charge transport parameters was investigated by replacing the conventional trioctylphosphine oxide (TOPO) surfactant with pyridine to provide closer contact between the organic and inorganic components. Electrical parameters of FETs with an active layer made of P3HT:CdSe QDs blend were determined, showing field-effect hole mobilities up to 1.1×10^?4 cm²/Vs. Incorporation of TOPO covered CdSe QDs decreased the charge carrier mobility while the pyridine covered CdSe QDs did not alter this transport parameter significantly.     

Cr2O3对(Co,Ta)掺杂的SnO2压敏电阻电学特性的影响

研究了Cr对(Co,Ta)掺杂的SnO2压敏材料电学性质的影响.当Cr2O3的含量从0增加到0.15mol%时,(Co,Ta)掺杂SnO2压敏电阻的击穿电压从206V/mm增加到493V/mm;1kHz时的相对介电常数从1968猛降至498;晶界势垒高度分析表明,SnO2晶粒尺寸的迅速减小是样品击穿电压增高、相对介电常数急剧降低和电阻率迅速增大的主要原因.对Cr含量增加引起SnO2晶粒减小的原因进行了解释.掺杂0.15mol% Cr2O3的SnO2压敏电阻非线性系数为24,击穿电压达498V/mm,在高压保护领域有很好的应用前景.     

Visible quantum cutting through downconversion in Eu3+-doped K2GdZr(PO4)3 phosphor

K₂Gd_1?xZr(PO₄)₃:Eu_x³⁺ (0.02 ≤ x ≤ 0.1, x is in mol.%) were prepared by solid-state reaction method and their photoluminescence properties were investigated in ultra-violet (UV) and vacuum ultra-violet (VUV) region. The phenomenon of visible quantum cutting through downconversion was observed for the Gd³⁺–Eu³⁺ couple in this Eu³⁺-doped K₂GdZr(PO₄)₃ system. Visible quantum cutting, the emission of two visible light photons per absorbed VUV photon, occurred upon the 186 nm excitation of Gd³⁺ at the ⁶G_J level via two-step energy transfer from Gd³⁺ to Eu³⁺ by cross-relaxation and sequential transfer of the remaining excitation energy. The results revealed that the efficiency of the energy transfer process from Gd³⁺ to Eu³⁺ in the Eu³⁺-doped K₂GdZr(PO₄)₃ system could reach to 155% and K₂GdZr(PO₄)₃:Eu³⁺ was effective quantum cutting material.     

Admittance spectroscopy of Ge quantum dots in Si

Self-assembled Ge quantum dots (QDs) embedded in Si-Schottky diodes were studied using admittance spectroscopy. A sample with one layer of Ge QDs embedded in p-Si was grown on a p⁺-substrate by molecular beam epitaxy and was processed into a Schottky diode structure. Activation energies have been determined as a function of the external bias voltage, which shifts the Fermi level in the sample. Two discrete activation energies of 318 and 303 meV have been extracted in the region of high bias voltage. They are identified as single and double charged QD ground state which is split up by a Coulomb charging energy. At approximately 40 meV lower activation energies several discrete levels attributed to excited dot states with a smaller energy separation of typical 5 meV are observed.     

Passively Q-switched Tm(3+)-doped silica fiber lasers

By splicing on a length of Ho(3+)-doped silica fiber onto a diode-pumped double-clad Tm(3+)-doped silica fiber, stable passive Q switching of the Tm(3+)-doped silica fiber laser is demonstrated. The formation of Q-switched pulses was found to depend on both the length and the position of the Ho(3+)-doped silica fiber that was inserted into the fiber laser cavity. For stable Q-switched pulse generation, Ho(3+)-doped silica fiber lengths shorter than twice the absorption depth must be used. For long Ho(3+)-doped silica fiber lengths, randomly generated pulses are observed at operating wavelengths longer than 2090 nm, which are attributed to intracavity pumping of the Ho(3+)-doped silica fiber.     

Comparative spectroscopy of (ErF3)(PbF2) alloys and Er3+-doped oxyfluoride glass-ceramics

We have prepared polycrystalline alloys x(ErF₃):(100 − x)(PbF₂), x = 1, 10. A comparison of their low temperature absorption and emission spectra with the respective spectra of transparent oxyfluoride glass-ceramics, 32(SiO₂)9(AlO_1.5)31.5(CdF₂)18.5(PbF₂)5.5(ZnF₂):3.5(ErF₃) mol%, indicates that the nano-crystalline phase in this glass-ceramic is Er³⁺-doped PbF₂.     

Thermo-optical parameters and dispersion of pure and Yb(3+)-doped KY(WO4)2 laser crystals

Dispersion of the principal refractive indices of pure and Yb(3+) (20 at.%)-doped KY(WO(4))(2) crystal is obtained in the visible range of the spectrum. A comparatively strong increase of the refractive indices (0.005-0.007) was observed for the doped crystal. Temperature dependence of the principal refractive indices is measured in the temperature region of 290-690 K. Thermo-optical coefficients (TOCs) of the first dn/dt and the second (1/2)(d(2)n/dT(2)) order are determined. It is found that TOCs are negative for n(p) and n(g) and positive for n(m) in both crystals. Doping increases dn(p)/dT almost two times more in comparison to that of the pure crystal, while for the other two indices TOC changes are insignificant.     

Physicochemical investigations of structurally enriched Sm3+ substituted SnO2 nanocrystals

Journal of Materials Science: Materials in Electronics - The present study portrays structural, magnetic, electrical, optical and electronic characteristics of polycrystalline pristine and...     

Dy3+:Y3Al5O12粉体的制备及发光性能研究

采用溶胶-凝胶/燃烧合成法制备了不同Dy3+掺量的Y3Al5O12发光体.分析了基质晶体结构、Dy3+掺量、Re3+的电荷半径比(Z/r)对Dy3+发光强度及发光颜色的影响.结果表明,Dy3+:Y3Al5O12样品的激发主峰位于353nm(6H15/2→6P7/2)附近;由于Dy3+所占据的Y3+位置具有D2对称性,具有一个反演对称中心,使得Dy3+的发射光谱以481nm蓝光发射为发射主峰,但黄蓝光发射强度之比(Y/B)随Dy3+离子浓度的变化很小.     

Eu3+掺杂Bi4Si3O12材料的制备和发光特性（英文）

采用传统的固相合成法制备了Eu3+掺杂的Bi4Si3O12发光材料.使用X射线粉末衍射技术对制备的发光粉体进行了表征.Eu3+掺杂的Bi4Si3O12材料的激发谱表明,在265 nm处强而宽的谱带对应于Eu3+→O2-之间的电荷转移跃迁带.在用紫外光激发的荧光光谱中,Eu3+掺杂的Bi4Si3O12材料在614 nm处有强的红光发射.材料的激发和发射光谱结果表明,Eu3+掺杂的Bi4Si3O12有望做为红色固体发光的候选材料.     

Excited state spectroscopy in carbon nanotube double quantum dots

We report on low-temperature measurements in a fully tunable carbon nanotube double quantum dot. A new fabrication technique has been used for the top-gates in order to avoid covering the whole nanotube with an oxide layer as in previous experiments. The top-gates allow us to form single dots and control the coupling between them, and we observe 4-fold shell filling. We perform inelastic transport spectroscopy via the excited states in the double quantum dot, a necessary step toward the implementation of new microwave-based experiments.     

Holographic image storage in eu(3+)-doped alkali aluminosilicate glasses

We demonstrate that holographic information can be stored in Eu(3+)-doped alkali aluminosilicate glasses. The holograms were developed by a two-beam mixing configuration with a write-beam wavelength (465.8 nm) corresponding to the (7)F(0) ? (5)D(0) transition of the Eu(3+) ions. The images were reconstructed either with the wavelength used to record them or with wavelengths below this transition (543.5 and 632.8 nm). We stored clear holographic images using a total writing power of 5 mW and an exposure time of 20 s. In addition, clear holograms were recorded with an exposure time of 200 ms when 100 mW of the writing power was used. The exposure time and the writing power required to obtain clear holographic images are dependent on the Eu(3+) concentration.     

Ni2+掺杂近化学计量比铌酸锂晶体的近红外发光特性

研究了Ni2+掺杂近化学计量比铌酸锂(Ni2+:SLN)晶体的近红外发光特性.用980 nm LD光激发,Ni2+:SLN单晶的近红外发光中心位于1087 nm,荧光峰半高宽约为72 nm.晶体荧光衰减特性的测定结果表明,其室温荧光寿命为～240μs.晶体的近红外的宽带发光,源于Ni2+离子八面体格位的3T2g(3F)...