Relaxation kinetics of Sm: Ce-doped CaS phosphors

Different samples of calcium sulphide (CaS):CaS(Sm) and CaS(Sm,Ce) phosphors have been prepared. To study the phosphorescence decay systematically, the samples were excited to a saturation using 259 nm line of xenon lamp and phosphorescence emission was monitored for a wavelength 569 nm of samarium. The trap depth has been evaluated by analyzing the decay curves. The observed decay could be explained satisfactorily by assuming a superposition scheme. The thermoluminescence properties of the doped CaS phosphors are also investigated in detail by computerized deconvolution technique of the glow curves obtained by UV irradiation.     

微波合成的纳米球形CaS∶Ag+荧光体的荧光光谱

在微波场作用下 ,快速合成了CaS∶Ag+荧光体 ,用X射线粉末衍射 (XRD)分析证实了它们是立方晶相。测定了它们的激发光谱和发射光谱 ,发现其发射峰位于 372nm、45 0nm和 5 77nm ,分别是由A′gCa V2 +S 中心的Ag+离子、间隙Ag+离子、A′gCa的Ag+离子和CaS基质自激活产生的 ,随着Ag+的掺杂浓度和助熔剂的改变 ,Ag+离子的几个发光中心互相转化 ,荧光体发出不同颜色的荧光。用扫描电镜 (SEM)观察了它们的晶体形貌和尺寸大小 ,结果表明CaS∶Ag+荧光体的晶体形貌都是球形的 ,但其粒径和晶体的分散性受Ag+的掺杂浓度和助熔剂的影响 ,出现了纳米晶 ( 7～ 10 0nm)和亚微米晶 ( 12 5～ 30 0nm)。     

Size effect in the optical second harmonic generation by silicon nanoparticles

A size effect has been revealed in the spectra of the second harmonic generated in a reflection from an amorphous silicon composite layer with inclusions of crystalline silicon (nanocrystallites) measured at room temperature: a decrease in the mean size of the nanocrystallites from 100 to 30 nm is accompanied by a shift of the spectral peak near 3.3 eV by 0.12 eV towards the short wavelengths and an increase in the peak width by a factor of 1.5. As a possible mechanism of this phenomenon, the effect of the structural defects on the parameters of the optical transitions in the nanocrystallites is discussed.     

ORGANOMETALLIC SYNTHESIS AND QUANTUM SIZE EFFECT OF CdSe NANOCRYSTALLITES

We have prepared nearly monodisperse CdSe nanocrystallites with diameters of 1-4 nm from the rapid pyrolysis of organometallic precursors in a hot coordinating solvent. The nanocrystal structures have been characterized by transmission electron microscopy and electron diffraction. From the absorption spectrum, we have observed the prominent peak of 1S-1S excitonic transition, which is obviously blue-shifted from the bulk bandgap and the largest shift is about 1.25 eV. We have used a theoretical model based on the tight binding approximation to analyze the quantum size effect of these nanocrystallites. The results have been compared with those of the effective mass approximation model.     

Effect of Fe,Co, Ni and Cd CO‒activation on luminescence emission and decay of CaS:Ce phosphors

Cathodoluminescence (CL), photoluminescence (PL), thermoluminescence (TL) spectra, and decay after laser beam excitation of cerium-activated CaS phosphors doped with Fe, Co, Ni or Cd have been investigated. These studies shed some light on the nature of luminescence centres and the association of various groups of traps with the dopants. Effect of concentiation variation of these four elements on emission and decay characteristics of CaS:Ce phosphor has been discussed. In contrast with the earlier publication [W. Lehmann and F. M. Ryan, J. Electrochem. Soc. 119, 275 (1972)] we have found that Ni is an effective killer, Cd ineffective and Co has no clearly observable effect. Fe has also been found to be an effective killer for CaS:Ce phosphors. Ni and Fe appear to be more effective quenchers for shorter wavelength emission band characteristic of Ce in CaS.     

CaS2：Eu的直流电致发光

制备了CaS,Se:Eu红色DCEL屏.在CaS:Eu中掺入少量Se可以改进DCEL性能.研究了Pb对CaS:Eu的影响.通过发射、激发光谱及衰减的测量,认为Pb2+敏化了Eu2+.与常规的CaS:Eu相比,CaS:Eu,Pb的DCEL效率和寿命都明显提高了.     

Luminescence properties of CaS:Ce, Sm nanophosphors

CaS:Ce, Sm nanophosphors were synthesized via solid state diffusion method. X-Ray diffraction confirmed the cubic crystalline phase of CaS:Ce, Sm nanoparticles. The particle size calculated using Debye-Scherrer formula was found to be 52 nm. The morphological investigations of the nanoparticles were made using TEM and found to have nearly spherical morphology with diameter 45-50 nm, which is in close agreement with the XRD result. The PL emission characteristics of CaS:Ce, Sm as a function of cerium and samarium concentrations have been studied and CaS:Ce_0.6Sm_0.4 system has maximum emission intensity, hence it was opted for further studies. The CaS:Ce_0.6Sm_0.4 system showed independent emission of Sm and Ce when excited at 330 and 450 nm, respectively. To study the energy transfer between cerium and samarium, the CaS:Ce_0.6Sm_0.4 was excited at wavelengths other than the excitation wavelengths of Ce (450 nm) and Sm (330 nm). The existence of Ce emission (at an excitation of 390 nm) even in the absence of Ce excitation band and Sm emission at an excitation of 405 nm, which is the excitation band of Ce, indicates the energy transfer at these two wavelengths. Thermoluminescence characteristics of ⁶⁰Co irradiated CaS:Ce_0.6Sm_0.4 have been investigated for different doses of 0.14-125 Gy. All the glow curves show a single peak at 475 K. With increasing dose, the intensity of this peak increases and a shoulder is formed on the lower temperature side at 415 K at 21 Gy of exposure. CaS:Ce_0.6Sm_0.4 shows almost linear dose dependence up to 125 Gy.     

CaS:Cu+磷光体的合成及发光性质

本文首先用X光电子能谱分析铜在硫化钙基质中是以一价形式存在的.在掺铜的硫化钙的激发光谱中,有三个吸收峰,峰位分别为268nm、307nm和400nm;在CaS:CuCu+的发射光谱中,产生四个发射峰,峰位分别为430nm、465nm、490nm和610nm.这四个发射峰分别由不同铜离子格位产生的.在Cas:CuCu+的热释发光曲线中,显示单一热释发光峰,峰值温度为120℃,该热释发光峰有可能用作紫外剂量材料.     

Anomalous thermally stimulated currents in CaS

Information on the nature of traps in CaS has been sought by studying the TSC behaviour in a range of samples. Results are in agreement with those reported previously and suggest that the TSC peak at 308 ± 3K is independent of the nature and concentration of dopant. Evidence is presented which indicates that surface states are responsible for the currents rather than the release of trapped charge from states within the band gap; the source of the charge carriers is uncertain. Simultaneous TSC and TL measurements on CaS:Ce, Cu indicate that the TL peak at 300K and the TSC peak at 308K are mutually independent.     

Photoluminescence Spectra of Eu3+-Doped Certain Powder Phosphors

The fluorescence properties of Eu³⁺-doped CaS, LaOCl, LaOF, YOCl and YOF powder phosphors are reported. These phosphors exhibited a reddish orange colour when excited in the UV. The photoluminescence spectra have been characterized by determining their stimulated emission cross-section values.     

Pb2+离子在CaS中的发光特性与应用

研究了单掺Pb^2 和共掺Pb^2 、Eu^2 离子的CaS 发光材料的荧光性质。Pb^2 的发射光谱位于蓝区，Eu^2 的发射光谱位于红区，实验结果表明，Pb^2 对Eu^2 荧光发射有很强的敏化作用。Pb^2在紫区有较强的吸收，说明Pb^2 、Eu^2 共激活的CsS材料是一种适用于高原寒冷地区的农用薄膜转光剂。     

Relaxing local modes and the theory of low-frequency Raman scattering in glasses

Raman scattering in glasses is investigated theoretically. The experimental Raman spectra of glasses exhibit a low-frequency peak (at ～10 cm^?1) that, as a rule, is attributed to vibrational modes of nanometer-sized structural units (nanocrystallites). It is established that the elastic moduli of nanocrystallites must necessarily be dependent on their sizes due to the Laplace pressure effect. A theory of the low-frequency peak is constructed using a realistic size distribution function of nanocrystallites with allowance made for the Laplace pressure effect and the dissipation of vibrational energy. Within this theory, the shape of the low-frequency peak and its evolution with temperature can be analyzed quantitatively. The proposed approach offers a physical interpretation of the experimental data and provides insight into the relation of the characteristic nanocrystallite sizes to the elastic moduli and surface tension coefficients of materials.     

掺Sb纳米ZnO的光致发光的研究

用柠檬酸盐法合成了不同掺杂浓度的纳米ZnO,粒径约为15nm。探讨了Sb掺杂对ZnO光致发光峰的影响。随着掺杂量的提高,样品的发射峰从428nm移至444nm。未掺杂ZnO的发光主要是源于电子从锌填隙形成的缺陷能级到价带顶的跃迁;随着掺杂量的提高,体系的氧空位增加,从而使得电子从氧空位所形成的缺陷能级到价带顶的跃迁占据主导,光致发射峰向长波方向移动。     

Post-irradiation annealing study of TLD-900 at low radiation doses

The fading behaviour of the thermoluminescent phosphor CaS0₄ :Dy, TLD-900, obtained from the Harshaw Chemical Company has been investigated up to 100 hours. Some experiments have been begun to investigate the effect of post-irradiation annealing (post-i.a.) on the stored TL signal.     

Green Emitting Cerium Doped CaS Whiskers Grown by Solid State Diffusion Method

Undoped and cerium doped Calcium sulfide (CaS) phosphors were synthesized using solid state diffusion method. The X-ray diffraction pattern revealed that both undoped and doped CaS crystallites have cubic structure with average crystallite size varying from 20 to 30 nm. Scanning electron micrographs indicated that Ce doped CaS phosphors were composed of whiskers with different dimensions and orientations. The optical properties of undoped and Ce doped particles were characterized using Photoluminescence (PL) and UV-Vis absorption spectroscopy. The PL emission spectrum of cerium doped CaS phosphors for an excitation wavelength 465 nm showed a main peak at 500 nm and a shoulder peak at 556 nm due to 5d?→?4f transition in Ce³⁺ ions. The variation of PL intensity with cerium concentration was investigated and the maximum PL intensity was obtained for a doping concentration of 3 wt.%. The optical band gap of the samples was estimated from the diffuse reflectance spectrum and was found to increase with increase in cerium concentration. The enhanced optical properties of these phosphors can be exploited in various optoelectronic devices including displays and bioimaging techniques.     

Effect of the growth conditions on infrared upconversion efficiency of CaS: Eu, Sm thin films

High-quality electron-trapping thin films CaS: Eu, Sm with red light output have been successfully deposited on quartz and single-crystal silicon substrates by electron beam evaporation (EBE) and radio frequency (RF) magnetron sputtering in vacuum and H₂S partial pressures. Infrared upconversion efficiency of CaS: Eu, Sm thin films under different growth conditions has been investigated by using ultrashort infrared (IR) laser pulse with 20 ps (full width at half-maximum (FWHM)). The results show that upconversion efficiency of CaS: Eu, Sm thin films depends strongly on growth conditions in spite of the existence of “exhaustion” phenomena. Microstructures identified by X-ray diffraction (XRD) indicate that crystallinity of CaS films relies on both substrate materials and growth conditions. The stoichiometric composition of CaS films was measured by secondary-ion mass spectrometry (SIMS). The post-annealing process was found to promote grain growth and activate strong luminescence so that it could obviously improve upconversion efficiency of CaS: Eu, Sm films, even though it had negative influence on transmittance and spatial resolution of these films. Received: 5 June 2000 / Accepted: 7 June 2000 / Published online: 23 August 2000     

Studies on luminescence properties and energy transfer in Ce/Dy co-doped CaS nano-phosphors

Luminescence properties of CaS:Ce co-doped with dysprosium has been studied. Ce/Dy co-doped CaS nanophosphors (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50, CaS:Ce_0.75Dy_0.25) were synthesized using the solid state diffusion method. The phase purity of the samples was confirmed using XRD data. The particle size was calculated using Debye–Scherrer formula and was found to be varying between 50 and 60 nm for all the three samples (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50 and CaS:Ce_0.75Dy_0.25). TEM image analysis of CaS:Ce_0.50Dy_0.50 shows nearly spherical particles with diameter varying between 50 and60 nm. One way energy transfer from Dy³⁺ to Ce³⁺ in CaS host has been investigated using photoluminescence studies. Thermoluminescence of these nanophosphors has been studied for 0.5 Gy–21 kGy dose of gamma rays and the dose linearity of CaS:Ce_0.50Dy_0.50 has been compared with CaSO₄:Dy (standard TL dosimeter). Linear behavior over a large dose range between 0.5 Gy and 21 kGy was found for CaS:Ce_0.50Dy_0.50 as compared to CaSO₄:Dy (nanocrystalline and microcrystalline) but it is found to be less sensitive than microcrystalline CaSO₄:Dy. To identify the peaks of Ce³⁺ and Dy³⁺ in CaS, the TL spectra of CaS, CaS:Ce, CaS:Dy and CaS:Ce_0.50Dy_0.50 were recorded. The addition of dopants does not add new peaks in CaS but aid to enhance the TL emission. The peaks in CaS may be associated to intrinsic traps in the host lattice.     

Preparation of ferromagnetic γ - Fe2O3 nanocrystallites by oxidative co-decomposition of PEG 6000 and ferrocene

Highly crystalline and ferromagnetic γ-Fe₂O₃ nanocrystallites were prepared by controlled oxidative co-decomposition of PEG 6000 and ferrocene at a temperature of 450 ^°C under air atmosphere. The morphology, crystalline structure and preliminary magnetic properties of the as-synthesized nanocrystallites have been characterized by using transmission electron microscope (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The highly crystalline γ-Fe₂O₃ nanocrystallites are in quasi-cubic shape with an average size of 30 nm and exhibit room-temperature ferromagnetism. The capping effect of PEG 6000 has also been investigated by thermogravimetry analysis (TGA) and Fourier transform infrared (FTIR) regarding controlling the size of the nanocrystallites and preventing the volatilization of ferrocene and thus raising the yield of the products. This simple method has a high yield of over 80% as well as low cost.     

纳米Ge颗粒镶嵌薄膜的Raman散射光谱研究

研究了镶嵌在ＳｉＯ_２介质中的不同尺寸（４—１６ｎｍ）纳米Ｇｅ颗粒的Ｒａｍａｎ散射谱特征，与大块标准Ｇｅ晶体的散射峰相比，观察到了理论预期的纳米半导体粒子的Ｒａｍａｎ散射峰的宽化和红移现象．采用声子限域模型较好地解释了实验结果．探讨了ＳｉＯ_２介质基体作用于镶嵌Ｇｅ粒子的压应力以及纳米Ｇｅ粒子的表面界面效应对Ｒａｍａｎ散射光谱的峰形、峰位变化所产生的影响 关键词：     

CaS∶Eu,Sm光存储材料的光谱特性

CaS∶Eu, Sm是一种典型的电子俘获型光存储材料,文章采用湿法在还原气氛中制备了CaS∶Eu, Sm粉末样品。测量了这种光存储材料的XRD、激发光谱、发射光谱、光激励发光光谱、热释光谱以及光激励发光衰减曲线。XRD结果表明样品在1 050 ℃晶格已经形成。光谱测试结果说明紫外光可激发该材料,作为信息写入光源。样品被紫外光源饱和激发后,用980 nm红外激光激励,发射出峰值位于635 nm的红光。光激励发光起初衰减较快,随后有一个较长的平缓期。且样品具有合适深度的陷阱能级,能够稳定存储信息。对CaS∶Eu, Sm的光存储机理进行了探讨。