GdVO4:Eu3+的热释光研究

GdVO4:Eu^3 有着十分优良的发光特性，它发光强度高，特别是具有很好的温度特性，在室温以上发光强度随温度的升高而增强，很利于在高温下使用此材料。本文对它的热释光进行了研究，其热释光峰值分别位于193，235和304K，根据计算可知它们的陷阱深度分别为0.39,0.47和0.61eV，陷阱的主要来源可能是F^ ,F和钒空位；Eu^3 掺入导致的晶格畸变，其中最主要的来源可能是空位导致的。     

Luminescence of CsBr:Eu films grown by liquid-phase epitaxy

By liquid-phase epitaxy from an aqueous alcoholic solution, we have obtained films of the well-known storage phospor CsBr:Eu, and we have studied their cathodoluminescence and photoluminescence (PL) spectra compared with the undoped CsBr films. We have established that the structure of the photoluminescence centers of the CsBr:Eu films when excited by laser radiation in the absorption band of the Eu²⁺ ions (λ = 337 nm) includes Eu²⁺-V_Cs isolated dipole centers and CsEuBr₃ aggregate centers, and also luminescence centers based on inclusions of hydroxyl group OH⁻ with the corresponding emission bands in the 440 nm, 520 nm, and 600 nm regions. We have studied the dependence of the spectra and the intensity of the photoluminescence for CsBr:Eu films on annealing temperature in air at 423–483 K, compared with analogous dependences for CsBr:Eu single crystals obtained from the melt. We have shown that annealing the films at T = 423–463 K leads to rapid formation of CsEuBr3 aggregate luminescence centers, while for T > 473 K thermal degradation of these centers occurs. We conclude that the observed differences between the photoluminescence spectra of CsBr:Eu films and CsBr:Eu single crystals may be due to additional doping of the films with OH⁻ ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 191–194, March–April, 2006.     

Time-resolved photoluminescence spectra of high-density InGaAs/AlGaAs quantum wire structures

We investigated the temperature dependence of the time-resolved photoluminescence (PL) spectra of high-density InGaAs/AlGaAs quantum wire (QWR) distributed-feedback laser structure on a submicron grating. A red-shift of peak in the time-resolved PL after photo-excitation was observed due to the relaxation of the photo-generated excitons from the entire QWR to localized centers at 10 K. On the other hand, at 60 K, no red-shift in the time-resolved PL spectra was observed since the localization centers are thermally activated and the excitons are delocalized.     

BeAl_6O_(10)晶体中单体铬和铬离子对的窄线发光

BeAl_6O_(10):Cr的荧光谱由宽带和七条窄线组成.在室温下,宽带和窄线发光的衰减时间极不相同.本文根据线强度的温度关系、浓度关系推论,三条窄而强的荧光线来自两种单体铬中心.另有两条稍宽的线来自铬离子对中心.宽带发射与这些窄线发射没有象BeAl_2O_4:Cr中那样的联系.     

Recording holograms on color centers in CaF2:Na crystals by light with different wavelengths

The absorption spectra and holographic characteristics of a CaF₂:Na crystal sample are measured at different wavelengths within the absorption band of colloidal centers, along with the same characteristics of the samples with holograms after their irradiation by incoherent UV light. Results of the study confirm the diffusion-and-drift mechanism of recording holograms on color centers in ionic crystals.     

Adsorption and decomposition of HNCO on Cu(111) surface studied by auger electron,electron energy loss and thermal desorption spectroscopy

No detectable adsorbed species were observed after exposure of HNCO to a clean Cu(111) surface at 300 K. The presence of adsorbed oxygen, however, exerted a dramatic influence on the adsorptive properties of this surface and caused the dissociative adsorption of HNCO with concomitant release of water. The adsorption of HNCO at 300 K produced two new strong losses at 10.4 and 13.5 eV in electron energy loss spectra, which were not observed during the adsorption of either CO or atomic N. These loses can be attributed to surface NCO on Cu(111). The surface isocyanate was stable up to 400 K. The decomposition in the adsorbed phase began with the evolution of CO₂. The desorption of nitrogen started at 700 K. Above 800 K, the formation of C₂N₂ was observed. The characteristics of the CO₂ formation and the ratios of the products sensitively depended on the amount of preadsorbed oxygen. No HNCO was desorbed as such, and neither NCO nor (NCO)₂ were detected during the desorption. From the comparison of adsorption and desorption behaviours of HNCO, N, CO and CO₂ on copper surfaces it was concluded that NCO exists as such on a Cu(111) surface at 300 K. The interaction of HNCO with oxygen covered Cu(111) surface and the reactions of surface NCO with adsorbed oxygen are discussed in detail.     

Farbzentren und Kolloide in abschreckend kondensierten Schichten von NaJ,CaF2 und SrCl2

By a simultaneous evaporation of NaI with excess alkali or alkaline earth metal onto a cooled substrate (T _K =20–150 K) highly disordered thin films are produced, which contain electron excess centers up to a concentration of more than 10²⁰ cm^?3. A complex optical absorption band peaking at 600 and 530 nm is found. The 600 nm band is mainly due to unperturbed F centers, whereas the 530 nm band is ascribed to perturbed F centers, whose symmetry is lowered to C_3v by a nearby Frenkel defect. Another optical transition of this F* center appears at about 600 nm in the dichroic spectrum, which is induced by polarized illumination at 20 K. The transition energies of the F* center are calculated by means of a semi-continuum model. A photochemical transformation of F* and F centers into one another is possible at 20 K. AboveT _K =220 K the excess metal is forming colloidal centers. Two absorption peaks at about 600 and 400 nm, respectively, are ascribed to different colloids, which are either embedded in the crystalline material (600 nm) or only adsorbed to the crystallites (400 nm). By annealing up to 350 K a particle growth and transformation take place. Amorphous quenched films of CaF₂ and SrCl₂ with excess alkaline earth metal reveal mainly colloidal absorption (except a weak F band in CaF₂). The colloids disappear by annealing above 150 K. This is believed to be closely connected with the crystallisation of the films.     

Diffraction losses of Nd:YAG and Yb:YAG laser crystals

Based on space-dependent rate equations, the lowest threshold input power for a diode end-pumped solid-state laser is obtained for the pump spot size w_p→0. However, as the pump beam waist is decreased, the thermally induced effects in the laser rod would be very high. Diffraction losses caused by radial and tangential variations of refractive index have been analyzed and compared for the Nd : YAG and the Yb : YAG at room temperature (300 K) and liquid-nitrogen temperature (77 K).     

Luminescence of nanocrystalline ZnS:Cu

Temperature dependent luminescence and luminescence lifetime measurements are reported for nanocrystalline ZnS:Cu²⁺ particles. Based on the variation of the emission wavelength as a function of particle size (between 3.1 and 7.4 nm) and the low quenching temperature (T_q=135 K), the green emission band is assigned to recombination of an electron in a shallow trap and Cu²⁺. The reduction in lifetime of the green emission (from 20 μs at 4 K to 0.5 μs at 300 K) follows the temperature quenching of the emission. In addition to the green luminescence, a red emission band, previously only reported for bulk ZnS:Cu²⁺, is observed. The red emission is assigned to recombination of a deeply trapped electron and Cu²⁺. The lifetime of the red emission is longer (about 40 μs at 4 K) and the quenching temperature is higher.     

氯化钠晶体的光致变色特性

系统研究了γ射线辐照和电子束轰击着色的氯化钠晶体的光致变色特性及其形成机理，在４４８Ｋ，着色晶体经几个激光脉冲照射就能有效地产生Ｆ→Ｃ转换，产生的胶体心尺度随着色剂量增加而增大，在着色氯化钠晶体中观测到吸收带位于６２５ｎｍ的新胶体心。在５２３Ｋ，可有效地产生Ｃ→Ｆ转换，实现了Ｆ和Ｃ心的可逆转换，在Ｆ带激光照射下，Ｆ→Ｃ转换主要通过Ｆ和Ｆ心光致电离后产生的可动缺陷来实现的，并从机理上提出简明的物理解     

Limit analysis for laser removal of micron contaminant colloidal silicon dioxide particles from the super-smooth optical glass substrate by pulse Nd:YAG laser

Multimode Nd:YAG pulse laser was applied to remove micron and submicron particles by vaporizing a thin paint film pre-coated on super-smooth optical substrate surface. By analyzing the poor absorption of the optical glass substrate to the irradiative Nd:YAG pulse laser, the removal mechanism of contaminated colloidal particles from the super-smooth surface through vaporization of a volatile solid film is described. A limit analysis was proposed to determine the lower and the upper threshold of laser fluence for cleaning the SiO₂ contaminants from super-smooth K8 optical substrate. Relevant experiments on laser cleaning of micron-polishing particles from super-smooth K8 optical substrate confirmed the usefulness of this method in assisting the selection of effective cleaning fluence for accomplishing high cleanliness, which was in a range of 80–90% of the predicted upper threshold.     

Anionische Silberzentren („B-Zentren“) in Alkalihalogeniden

It is proposed that negatively charged silver ions on anion sites are responsible for theB bands found in silver doped alkalihalides. Experimental investigations confirming this model of theB center are presented. Optical absorption and emission ofB centers were measured in seven alkalihalides in the temperature range from 450 to 4 °K. Configuration coordinate diagrams were obtained for KCl, KBr, and KI. A chemical method was used to determine the charge of theB center. Thermal or optical excitation causes theB centers to dissociate into neutral silver atoms andF centers. The Ag⁰ centers are bound to interstitial positions at low temperature. At high temperature they collect together forming colloidal centers. TetragonalB _A centers were formed during optical bleaching of theB band in mixed crystals of the type KCl+ΔNaCl. Their absorption and emission spectra, optical orientation, and polarized emission were investigated. These properties are shown to be similar to those ofF _A centers.B _A fluorescence polarized almost completely in the [100] direction was observed. A Jahn-Teller splitting of theB absorption band was resolved in RbCl at low temperature. The splitting confirms the configuration5s² for the Ag^? ion. The results are compared with those for the isoelectronic centers In⁺ and Sn⁺⁺. Thin films of alkalihalides containing small amounts of silver, copper, or thallium were condensed simultaneously with alkali vapor. New bands in the UV region were found, possibly due to Cu^? and Tl^? centers.     

<Superscript>29</Superscript>Si nuclear spin relaxation in microcrystals of plastically deformed Si: B samples

Single crystals and microcrystals Si: B enriched with ²⁹Si isotopes have been studied using nuclear magnetic resonance and electron paramagnetic resonance (EPR) in the temperature range from 300 to 800 K. It has been found that an increase in the temperature from 300 to 500 K leads to a change in the kinetics of the relaxation of the saturated nuclear spin system. At 300 K, the relaxation kinetics corresponds to direct electron–nuclear interaction with inhomogeneously distributed paramagnetic centers introduced by the plastic deformation of the crystals. At 500 K, the spin relaxation occurs through the nuclear spin diffusion and electron–nuclear interaction with an acceptor impurity. It has been revealed that the plastic deformation affects the EPR spectra at 9 K.     

Cr^4＋：YAG,Cr^4＋：Mg2SiO4近红外荧光辐射温度特性研究

测量了Ｃｒ＾４＋，ＹＡＧ、Ｃｒ＾４＋，Ｍｇ２ＳｉＯ４晶体在室温和液氮温度下的荧光光谱，吸收光谱和激发态寿命，讨论了温度变化时，两种晶体中Ｃｒ＾４＋近红外辐射积分强度变化与激光发态寿命变化的关系，得出结论：在７７Ｋ￣３００Ｋ范围内，Ｃｒ＾４＋的＾３Ｔ２能级荧光辐射截面本身受温度影响不大，Ｃｒ＾４＋辐射荧光的变化，主要是由无辐射弛豫速率随温度变化而引起的。     

Thermo-and photostimulated luminescence of CaI2: Tl and CaI2: Pb crystals

Thermo-and photostimulated luminescence of CaI₂: Tl and CaI₂: Pb scintillation crystals under optical and X-ray excitation is studied. It is shown on the basis of the results obtained with account for the data of studies of photo-and X-ray-luminescent properties of these scintillators that Tl⁺ and Pb²⁺ ions form complex capture centers with host defects. These centers are responsible for the thermostimulated luminescence in the temperature range of 150–295 K, and the centers of charge carrier trapping are spatially separated from the centers of recombination emission. An assumption is made that thermo-and photostimulated luminescence of CaI₂: Tl and CaI₂: Pb crystals under optical excitation is observed mainly due to the delocalization of charge carriers from hydrogen-containing centers responsible for the excitation band at 236 nm and the photoluminescence of CaI₂ with a maximum at 395 nm. The luminescence of CaI₂: Tl crystals in the 510-nm band and CaI₂: Pb crystals in the 530-nm band is determined by the radiative decay of near-activator excitons.     

Transformation of As-Grown Phosphorus-Related Centers in HPHT Treated Synthetic Diamonds

This communication presents new data on phosphorus-containing centers in synthetic diamonds grown in the P–C system by high-pressure high-temperature (HTHP) method and annealed in the temperature range of 2,073–2,573 K. The electron paramagnetic resonance (EPR) study has shown that as-grown at 1,873 K diamonds contain single substitutional nitrogen (P1) and single substitutional phosphorus (MA1) centers. The main part of the spin density in the MA1 center locates on the carbon atom C₁ separated from phosphorus by one carbon atom. HPHT annealing (7 GPa, 2,073–2,273 K) results in aggregating substitutional nitrogen and phosphorus atoms. On the first step of annealing (2,073 K) of as-grown diamonds nitrogen–phosphorus NIRIM8 (NP1) centers are created. It is supposed that nitrogen and phosphorus atoms in this center are separated by two carbons. Further temperature increasing shifts the nitrogen atom toward phosphorus and creates two new nitrogen–phosphorus centers NP2 and NP3 with the supposed structures C₁–N–C–P and N–P–C₁, respectively. The main part of the spin density in MA1, NIRIM8 (NP1), NP2 and NP3 is located on the carbon atom C₁. Annealing these samples in the temperature range of 2,073–2,273 K has shown vanishing of NIRIM8 and increasing of NP2 and NP3 centers. HPHT annealing of diamonds at 2,573 K significantly changes the electron paramagnetic resonance (EPR) spectra: all previous nitrogen–phosphorus centers disappear and two new phosphorus centers NP4 and NP5 are created. Features of these centers are g ≈ 2.001 and high spin density located on the phosphorus atoms. The NP5 center is sensitive to X-ray irradiation and low-temperature annealing. The EPR spectra of both these centers are due to the hyperfine structure of one phosphorus atom. The structures of all phosphorus-containing centers are discussed.     

BaFCl:Eu2+光激励读出过程中两种F色心的差异

研究了紫外线辐照下BaFCl:Eu²⁺的光激励发光性质.测定了在不同温度下经紫外线辐照后的光激励谱,变化范围为10—300K同时研究了两种F色心的光激励发光强度在激励读出过程中随温度的变化关系.分析了光激励谱产生差异的原因. 关键词：     

均相条件下NO与CO、NCO的反应机理研究

基于量子化学密度泛函理论研究了NO与CO、NCO在均相条件下的反应机理并进行了动力学和平衡常数的分析. CO与NO的均相反应存在两条反应路径：两者首先反应形成中间体CNO₂,CNO₂不易稳定存在,其继续与CO、NO反应分别生成NCO、N₂O. NCO的生成速率大于N₂O,但两条反应路径的反应速率常数都很小.与已发现的反应路径相比,反应中间体CNO₂可以降低均相条件下CO与NO的反应能垒,分析发现CNO₂中的N原子是易发生反应的活性位点. NCO与NO的反应同样存在两条路径,优势反应路径随温度升高而改变,但非优势路径对反应的贡献不能忽略,分析平衡常数可知N₂的存在对反应影响可以忽略,因此燃烧环境中NCO与NO的反应既生成N₂O和CO,也生成N₂和CO₂.     

Effects of the dark-exciton state on photoluminescence dynamics in surface-modified CdS quantum dots prepared by a colloidal method

We have investigated exciton dynamics in surface-modified CdS quantum dots (QDs) prepared by a colloidal method. The size- and surface-controlled CdS QDs have been successfully prepared by using a size-selective photoetching and surface modification technique. The decay profiles exhibit an unusual temperature dependence: increase of the decay time with increase in temperature. The temperature dependence of the decay profiles can be explained in terms of a three-level model including the exciton state with a triplet origin, the so-called dark-exciton state.     

Thermal decay of photochromic color centers in CaF2, SrF2, and BaF2 crystals doped by La and Y impurities

The absorption spectra of photochromic centers in CaF₂, SrF₂, and BaF₂ crystals doped by La and Y impurities and thermal decay of the centers in the temperature range 80–600 K are investigated. Under low-temperature x-ray irradiation, ionized photochromic color (PC⁺) centers are generated in La- and Y-doped CaF₂ crystals and in a La-doped SrF₂ crystal. It is revealed that, upon heating of the CaF₂-LaF₃ crystal, PC⁺ centers are transformed into photochromic color (PC) centers. In the SrF₂-YF₃ crystal irradiated at room temperature, photochromic color centers are generated as well. All color centers decay at a temperature of approximately 600 K. After irradiation of the BaF₂-YF₃ crystal at a temperature of 80 K, absorption bands are observed at energies of 2.25 and 3.60 eV, which are related to neither PC centers nor PC⁺ centers.