Spectral properties of Pr:CNGG crystals grown by micro-pulling-down method

Pr~(3+)-doped calcium niobium gallium garnet(Pr:CNGG) single crystals with different Pr~(3+)concentrations are successfully grown by the micro-pulling-down(μ-PD) method. The crystal structure, room-temperature absorption spectra,and fluorescence spectra of Pr:CNGG crystals are measured and discussed. The fluorescence results indicate their large dependence on the doping concentration. The fluorescence lifetime of the ~1D_2 energy level is also determined. The results indicate that Pr:CNGG crystal could be a potential solid-state laser gain medium.     

Growth and luminescent properties of Yb—doped oxide single crystals for scintillator application

Rod-shaped (Lu_1−xYb_x)₃Al₅O₁₂ with x=0.05, 0.15, 0.30 and (Y_1−xYb_x)AlO₃ with x=0.05, 0.10, 0.30 single crystals were grown by the micro-pulling-down method. Edge-defined film-fed growth method was used to prepare (Y_0.9Yb_0.1)VO₄ crystal, while Ca₈(La_1.98Yb_0.02)(PO₄)₆O₂ crystal was grown by the Czochralski method. Luminescence of these crystals was studied with main attention paid to the charge transfer emission of Yb³⁺. Temperature tuned decay times in the time scale of units—tens of nanosecond was measured as a feature possibly interesting for an application in scintillation detectors in positron emission tomography.     

Tribological properties of aluminum oxide single crystals grown by the Stepanov method

The friction coefficient and relative wear rate of the aluminum oxide single crystals grown by Stepanov much have been determined for dry friction and water lubrication of different material combinations. A comparative evaluation of the surface fatigue strength of aluminum oxide singleand polycrystals is performed.     

Optical properties of Ni-doped single crystals grown by floating zone method

The single crystal growth conditions and spectroscopic characterization of Ni-doped MgGa₂O₄ with inverse-spinel structure crystal family are described. Single crystals of this material have been grown by floating zone method. Ni-doped MgGa₂O₄ single crystals have broadband fluorescence in the 1100–1600 nm wavelength range, 1.6 ms room temperature lifetime, 56% quantum efficiency and stimulated emission cross section at the emission peak. This new material is very promising for tunable laser applications covering the important optical communication and eye safe wavelength region.     

Recombination processes in lanthanum beryllate single crystals doped with Ce3+ and Pr3+ ions

The paper presents experimental results on recombination processes in lanthanum beryllate (BLO) single crystals (undoped BLO, and doped with 0.5 at % by Ce³⁺ and Pr³⁺ ions) obtained using XRL-spectroscopy at T = 8, 80 and 290 K and thermoluminescence technique in the temperature range of 8–650 K. The paper discusses spectra of the steady-state XRL-luminescence recorded in the energy range from 1.5 to 6.2 eV at different temperatures between 8 and 290 K; temperature dependences of XRL intensity recorded in the temperature range from 8 to 650 K; thermoluminescence glow curves recorded in spectral-integrated regime after X-ray exposure at T₀ = 8 or 290 K.     

Dislocations in GaAs single crystals grown by the Czochralski method

The influence was studied of growth conditions on the dislocation density in gallium arsenide single crystals grown by the Czochralski method from a gallium-enriched melt. Etching in a solution of 1 part cone. HNO₃ and 2 parts H₂O served to determine the dislocation density across and along a single crystal. The dislocation density along the crystal was found to depend mainly on the angle of crystal diameter increase.     

Centimeter-size BiFeO3 single crystals grown by flux method

A narrow part of Fe₂O₃–Bi₂O₃ phase diagram was re-investigated in order to elaborate single crystals of the multiferroic BiFeO₃ (BFO). Centimeter-size single crystals were successfully obtained by flux method, and present a preferred growth direction. X-ray diffraction studied have highlighted that the growth direction is along the polar axis [111] _r of the structure. The stability of BFO versus temperature (reversible ferroelectric transition followed by multiple irreversible decompositions) is discussed in the light of Differential Scanning Calorimetry (DSC) analysis performed between 25 and 1400°C.     

Lu2SiO5:Ce and Y2SiO5:Ce single crystals and single crystalline film scintillators: Comparison of the luminescent and scintillation properties

The paper is dedicated to development of scintillators based on the single crystalline films of Ce³⁺ doped Lu₂SiO₅ (LSO:Ce) and Y₂SiO₅ (YSO:Ce) orthosilicates grown by Liquid Phase Epitaxy method onto YSO substrates from melt-solutions based on the PbO–B₂O₃ flux. We also compare the luminescent and scintillation properties of Ce doped LSO:Ce and YSO:Ce single crystalline films with those of their single crystal counterparts, grown by the Czochralski method.     

温度梯度法生长的Ce:YAlO3高温闪烁晶体的光谱分析

采用温度梯度法生长了熔体掺杂Ce浓度为1at%的YAlO3晶体,对于其吸收光谱、荧光光谱和x射线激发发射谱进行了表征分析.根据吸收光谱提出了一个色心模型,从而成功的解释了为什么刚生长出的晶体为粉红色,而分别经氢气和空气在1400℃退火后均能变为无色的现象和退火以后吸收光谱发生的显著变化.温度梯度法生长的Ce:YAP在330nm处存在着一定程度的自吸收和自激发.光致激发发射谱的发射主峰在368nm,而x射线激发发射谱的主发射峰红移至391nm,这表明在x射线激发下,晶体对发射光的自吸收将会减少.另外在x射线激发发射谱上,经H2退火和空气退火后的样品其发射强度比未退火的晶体要强.     

Electrical properties of doped single crystals of ZnSb

The conductivity , thermo-emf , and Hall constant R are reported for the range 100 °-490 ° K for ZnSb crystals doped with Ag, Au, Ga, In, Sn, Pb, and Te. Ag, Au, sn, and Pb act as acceptors, while In and Te increase the hole concentration, increase , and leduce . This occuis at relatively high concentrations by foimation of InSb and ZnTe molecules. Ga in ZnSb acts as a donor (compensating) component.     

Effects of Cd compensation on the photoluminescence of Cd1-xZnxTe single crystals grown by the modified Bridgman method

In order to deal with the phenomenon of Cd evaporation during the growth of Cd_1-xZn_xTe (x=0.1) crystals, Cd compensation was adopted during the growth by adding excess Cd into the raw materials. Photoluminescence (PL) spectra were used to investigate the effects of Cd compensation on the properties of Cd_1-xZn_xTe. A free exciton (FE) peak appeared in the near band-edge region after Cd compensation, which indicated that the concentration of Cd vacancies (V_Cd) was reduced in Cd_1-xZn_xTe crystals by Cd compensation. The donor–acceptor pair (DAP) peak became dominant in the PL spectrum and its first and second order phonon replica could also be easily identified after Cd compensation, which was only a weak hump in the case of Cd_1-xZn_xTe crystals without Cd compensation. It possibly meant that impurities of Al and In were released from the V_Cd-related complexes. In addition, the deep energy level transition D peak, decreased obviously after Cd compensation, which confirmed that Cd compensation could reduce the dislocation density effectively. PACS 71.20.Nr; 71.55.Gs; 78.55.-m     

Growth and optical properties of Hf,Ce co-doped lithium niobate crystals

In this paper, a series of Hf,Ce co-doped lithium niobate crystals with various HfO₂ concentrations were grown by Czochralski method. The ultraviolet-visible absorption spectra and the infrared transmittance spectra were measured to study defect structure of the crystals. The optical damage resistance was measured by the transmitted facula distortion method. The results showed that the optical damage resistance of Hf:Ce:LiNbO₃ was greatly improved when the Hf-doping concentration was above 4 mol%.     

Growth and electric properties of NaNbO3 single crystals doped with Mn

Single crystals of NaNbO₃ doped with Mn were grown. The precipitation of Mn was observed and the Mn concentration determined. The Mn dopant introduced causes variations in the properties investigated near the phase transition. The mechanism by which the Mn influences the phase transition parameters is discussed.     

Photoluminescence and EPR studies on gamma irradiated Ce doped potassium halide single crystals

Electron Paramagnetic Resonance(EPR), Photoluminescence(PL), Thermoluminescence (TL) and other optical studies of γ-irradiated KBr, KCl:Ce³⁺ single crystals. Cerium when doped into the KBr, KCl is found to enter the host lattice in its trivalent state and act as electron trap during γ-irradiation, thereby partially converting itself to Ce²⁺. The Photoluminescence(PL) spectra of both KCl and KBr crystals doped with Ce exhibit the strong blue emissions of Ce corresponding to ⁵d(²D)→²F_5/2 and ⁵d(²D)→²F_7/2 transitions. The defect centers formed in the Ce³⁺ doped KBr and KCl. Crystals are studied using the technique of EPR. A dominant TL glow peak at 374, 422 K and KCl:Ce³⁺ at 466, 475 K is observed in the crystal. EPR studies indicate the presence at two centers at room temperature. Spectral distribution under the thermoluminescence emission(TLE) and optically stimulated emission(OSL) support the idea that defect annihilation process to be due to thermal release of F electron in KBr, KCl:Ce³⁺ crystals. Both Ce³⁺ and Ce²⁺ emissions were observed in the thermoluminescence emission of the crystals.     

Dielectric properties of titanium and gadolinium doped MgO single crystals

The dielectric properties of titanium doped magnesium oxide (Ti/MgO) and gadolinium doped magnesium oxide (Gd/MgO) single crystals have been measured at room temperature over the frequency range 500 Hz to 50 kHz. For both the crystals, the dielectric constant is found to be independent of frequency and the ac conductivity Re{_ae} agrees well with the relation Re{_ae} ⁿ , being the angular frequency with n=0.84±0.05 for Ti/MgO andn=0.81±0.03 for Gd/MgO. The data fits well with the relation ^n–1(n<1), being the dielectric loss factor. An explanation may be found on the basis of the hopping phenomenon.     

Electrical properties of CdSb single crystals doped with silver

A study is made of the electrical and thermoelectrical properties of CdSb single crystals weakly and heavily doped with silver. The electrical conductivity, the Hall effect and the thermoelectric force in intrinsic conduction are studied on samples of CdSb oriented in the direction of the crystal-lographic axisb. The activation energy of the acceptors is determined as well as the density of states effective mass and their dependence on the temperature and concentration, and the mobility of holes is studied.     

Electronic properties of C60 single crystals doped with lithium by electrodiffusion

Diffusion of lithium cations in C₆₀ single crystals driven by electric field has been detected and studied. A novel technique for fullerene crystal doping based on injection of ions through a “superionic crystal/C₆₀ single crystal” heterojunction has been suggested. It has been found that lithium doping of C₆₀ single crystals brings about an ESR signal, and this signal as a function of time has been investigated. The electronic conductivity in Li_xC₆₀ crystals has a nonmetallic nature. Reflection spectra measured in the IR band have shown that the reflectivity due to free electrons gradually decreases with time, which correlates with the evolution of signals due to ESR and microwave conductivity. Lithium doping of crystals increases the oscillator strength of the T _1u (4) vibrational mode and shifts it to lower frequencies (from 1429 cm⁻¹ to 1413 cm⁻¹), which indicates that one electron is present at the C₆₀ molecule, and this fact may be treated as evidence that the LiC₆₀ phase is generated in a C₆₀ crystal. Zh. éksp. Teor. Fiz. 116, 1706–1722 (November 1999)     

Ferroelectric properties of doped triglycine sulfate crystals grown at negative temperatures

The effect of Cr³⁺ impurity ions on the dielectric and pyroelectric properties of triglycine sulfate crystals grown at temperatures below 0°C is studied. The Curie temperature T _C of the chromium-containing crystals is 0.2–0.4°C lower than that of the impurity-free crystals grown at conventional temperatures. A stable reproducibility of the results of the pyroelectric measurements for the crystals studied is established, which indicates that the polar state in crystals is stabilized by growth defects.     

Effect of surface states on luminescent properties of CdS single crystals

The luminescent properties of CdS single crystals excited by strongly absorbed light have been investigated for accumulation and depletion layers near the surface. The spectral distribution and change of intensity in maxima of emission bands were measured as functions of surface potential being varied by electric field (the luminescence field effect, LFE). Emission bands under examination were: r-band (λ_max = 1.03 μm), k-band (λ_max = 0.72 μm), o-band (λ_max = 0.62 μm) and IR-2 band (1.5–2.2 microm). The effects found (non-monotony of LFE for accumulation surface layers, the selectiveness of field action) indicate that the centres of red luminescence in the crystals studied are situated mainly near the surface or on the surface itself.