Electroluminescence of CaSO4: Sm phosphors

CaSO₄ phosphors activated with Sm³⁺ impurity in varying concentrations have been prepared and their electroluminescence systematically studied. The voltage and frequency dependence of brightness is discussed and conclusions are drawn regarding the possible mechanism involved in the process.     

ac anddc electroluminescence in CaS:Cu,Sm phosphors

Theac anddc electroluminescence in CaS:Cu, Sm have been investigated. The luminescence spectra show three peaks in the visible region. The brightness-voltage dependence satisfies the relationB=B ₀ exp (−b/V ^1/2) with two modes of variation. The nature of this dependence indc andac at different frequencies is discussed. The electroluminescence brightness also depends on the temperature of the phosphors and shows a peak around 80.0;C. The electroluminescence efficiency increases with applied voltage up to 2200 V and this dependence on V is explained on the basis of a transport process of the Schottky emission type.     

Synthesis of CaSO4:Dy,CaSO4:Eu3+ and CaSO4:Eu2+ phosphors

${\mathrm{CaSO}}_4:\mathrm{Dy}$ is a well-known phosphor for radiation dosimetry using thermoluminescence. ${\mathrm{CaSO}}_4:\mathrm{Eu}$, phosphors also find applications in radio-photoluminescence dosimetry and PLLCD. Various syntheses of these phosphors are described and optimum procedures are suggested. Effects of various preparation methods on luminescence characteristics are discussed in terms of elimination of unwanted impurities, grain size, etc.     

用光电离技术探测钐原子的奇宇称束缚激发态的光谱

采用光电离探测方法,对钐原子奇宇称束缚激发态进行了系统研究.通过设计三条不同的激发路径, 采用共振激发方式,先将钐原子分三步从基态激发到不同的束缚激发态,然后采用光电离手段对其进行探测. 通过对第三步激发光的波长进行大范围的扫描,在同一能域内获得了三组不同的光谱. 通过比对三条路径所得到的三组光谱,不仅精确确定了大量奇宇称束缚激发态的能级位置, 而且还获得了相应跃迁的相对强度的信息.最后,通过运用三条不同的激发路径的选择定则, 还确定了上述能级的总角动量. 关键词： 钐原子 束缚激发态 奇宇称 光电离探测     

Analysis of the phosphorescence of thianthren crystals

Summary The room temperature phosphorescence of crystalline thianthren in the 1.6–3.3 eV energy region has been measured using time delays going from 0.03 to 9.5 ms. The time dependence of the emission spectra which show the presence of three resolved bands, was analysed by means of a numerical best-fitting procedure, and the results obtained have been compared with those predicted by means ofab initio and semiempirical molecular orbital calculations.     

Phenylalanine fluorescence and phosphorescence used as a probe of conformation for cod parvalbumin

The fluorescence emission and triplet absorption properties of phenylalanine in cod fish parvalbumin type II, a protein that contains no Trp or Tyr, was examined in the time scale ranging from nanoseconds to microseconds at 25°C in aqueous buffer (pH 7.0). In the presence of Ca(II), the decay of fluorescence gave two lifetimes (5.9 and 53 ns) and the triplet lifetime was 425 s. Upon removal of Ca, the fluorescence intensity decreased to values approaching that for free Phe, while the longest fluorescence decay component was 17 ns. At the same time, the decay of triplet showed complex nonexponential kinetics with decay rates faster than in the presence of Ca. Quenching and denaturation analyses suggest that the Phe's are present in a hydrophobic environment in the Ca-bound protein but that the Ca-free protein is relatively unstructured. It is concluded that Phe luminescence in proteins is sensitive to conformation and that the long lifetime of Phe excited states needs to be considered when studying its photochemistry in proteins.     

Steady-state fluorescence and phosphorescence spectroscopic studies of bacterial luciferase tryptophan mutants

Bacterial luciferase, which catalyzes the bioluminescence reaction in luminous bacteria, consists of two nonidentical polypeptides, and . Eight mutants of luciferase with each of the tryptophans replaced by tyrosine were generated by site-directed mutagenesis and purified to homogeneity. The steady-state tryptophan fluorescence and low-temperature phosphorescence spectroscopic properties of these mutants were characterized. In some instances, mutation of only a single tryptophan residue resulted in large spectral changes. The tryptophan residues conserved in both the and the subunits exhibited distinct fluorescence emission properties, suggesting that these tryptophans have different local enviroments. The low-temperature phosphorescence data suggest that the tryptophans conserved in bot the and the subunits are not located at the subunit interface and/or involved in subunit interactions. The differences in the spectral properties of the mutants have provided useful information on the local environment of the individual tryptophan residues as well as on the quaternary structure of the protein.     

Laser-excited electronic fluorescence: Self-quenching and quenching of CS2 vapour

Summary Using a laser-induced fluorescence technique, we have measured lifetimes of CS₂ as functions of pressure, collecting the emission at various wave-length regions. We have obtained quenching rate constants for pure CS₂ and CS₂ plus CH₃CN and CO₂ as collision partners. When the emission is collected at a very long wave-length, evidence is given of vibrational relaxation in the singlet state which leads to the existence of a low-energy pathway of intersystem crossing. Two different long-lived states are also detected in the wave-length region centred at 5860 ?, one in the low-pressure regime and the other at pressures above 0.2 Torr approximately. Quenching rate constants of triplet CS₂ by CO₂ are about the same for both long-lived states, suggesting that vibrational relaxation could occur in the triplet state as well.

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Riassunto Usando una tecnica a fluorescenza indotta da laser, sono state misurate le vite medie di CS₂ in funzione della pressione, raccogliendo le emissioni in varie regioni di lunghezza d'onda. Si sono ottenute costanti di spegnimento per CS₂ puro e CS₂ piú CH₃CN e CO₂ come associati nella collisione. Quando si registra emissione a lunghezza d'onda molto grande, si prova l'esistenza di rilassamento vibrazionale nello stato di singoletto che porta all'esistenza di un percorso a bassa energia dell'incrocio intersistemico. Sono anche determinati due differenti stati a lunga vita nella regione di lunghezza d'onda centrata a 5860 ?, uno nel regime di bassa pressione e l'altro approssimativamente a pressione sopra i 0.2 Torr. Le costanti di spegnimento del tripletto CS₂ mediante CO₂ sono quasi le stesse per entrambi gli stati a lunga vita, e ciò suggerisce che il rilassamento vibrazionale potrebbe verificarsi anche nello stato di tripletto.

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Резюме Используя технику лазера, возбужденного флуоресценцией, мы измеряем времена жизни CS₂, как функцию давления, собирая излучение в различных областях длин волн. Мы получаем постоянные скорости гашения для чистого CS₂ и для CS₂ плюс CH₃CN и CO₂, которые участвуют в соударениях. Когда излучение собирается для очень больших длин волн, то отмечается вибрационная релаксация в синглетном состоянии. Были обнаружены два различных долгоживущих состояния с длиной волны при 5860 ?, одно при низком давлении, а другое при давлениях около 0.2 тор. Постоянные скорости гашения триплетного CS₂, обусловленные CO₂, оказываются примерно одинаковыми для обоих долгоживущих состояний. Этот факт свидетельствует о том, что вибрационная релаксация может иметь место также в триплетном состоянии.

     

Decay characteristics of SrS:Nd phosphors

The phosphorescence decay of a series of strontium sulphide microcrystalline phosphors prepared with varying amounts of neodymium as an activator has been studied at room temperature. The decay obeys the relationI =I ₀ t ^−b withb lying between 0·35 and 0·98. The trap depths have been evaluated by peeling off logI-t curves. The results show that the distribution of trap levels is likely to be quasi-uniform and the process of retrapping during luminescence is negligible.     

Thermoluminescence of x-irradiated CaSO4:Dy phosphors and role of Na2SO4 as a charge compensator

The thermoluminescence of x-irradiated CaSO₄: Dy phosphors has been studied for diverse activator concentrations. The concentration-dependence of these phosphors on the increase of glow peak intensities has been found to be remarkable. For higher concentration of dysprosium the concentration quenching effect has been observed. This has been attributed to the resonant transfer of energy from one activator atom to another, bringing the possible migration of energy in a solid, which is likely to get dissipated without luminescence, at the quenching site itself. The effect of irradiation time on the glow peak intensities reveals the initial linearity and a subsequent decrease indicating the possible radiation damage. The role of Na₂SO₄ as a charge compensator has been studied in detail. An attempt has been made to unravel the type of kinetics involved in the process, by calculating the activation energies by different methods. It has been concluded that the type of kinetics involved in the process is bimolecular.     

Effect of pressure on structure and fluorescence of SrFCL: Sm2+

Abstract

Lattice parameters of SrFCl have been measured by powder x-ray diffraction up to 38 GPa. Furthermore, energy levels and crystal field parameters of Sm²⁺ in SrFCl have been determined from fluorescence spectra at 100 K under pressures up to 10 GPa.     

X射线激发荧光光谱仪的建立及闪烁晶体发光表征

利用X射线作为激发光源,自行组装并实现计算机控制的X射线激发荧光光谱仪.介绍了X射线激发荧光光谱仪的建立及其结构特性.该仪器具有时间分辨率高、测量动态范围大、使用方便等优点,可应用于晶体、粉末和液体等各种样品的测量,该仪器同时还具有很强的扩展性.     

CaWO4：Sm3+荧光粉的发光性质及其能量传递机理

采用沉淀法制备了不同Sm³⁺掺杂浓度的白钨矿结构CaWO₄荧光粉材料. 对CaWO₄:Sm³⁺ 材料的光致发光性质的研究结果表明, 在404 nm光照下样品可以实现色纯度较高的红光发射, 而短波紫外240 nm光照下除Sm³⁺的特征发射外还能观察到CaWO₄自激发发射, 能够获得较强的白光; 实验发现Sm³⁺掺杂浓度为2%时样品的发光强度最高; 通过对实验数据的分析确定了Sm³⁺之间的能量传递类型为电偶极-电偶极相互作用, 并计算了能量传递的临界距离大约为2.0 nm. 关键词： 光致发光 4：Sm³⁺')" href="#">CaWO₄：Sm³⁺ 荧光寿命 能量传递     

UV-induced photoluminescence and thermally stimulated luminescence of CaSO4:Eu and CaF2:Tb3+ phosphors

Ultraviolet radiation induced changes in photoluminescence (PL) and thermally stimulated luminescence (TSL) of europium activated calcium sulphate (CaSO₄:Eu³⁺, Eu²⁺) and terbium doped calcium fluoride (CaF₂:Tb³⁺) phosphors have been studied. PL measurements suggest conversion of Eu³⁺ to Eu²⁺ on 254 nm irradiation corresponding to charge transfer band of Eu³⁺ ions and reduction of Eu²⁺ ions with 365 nm illumination representing a f–d transition of Eu²⁺ ions. Similar studies carried out on CaF₂:Tb³⁺ phosphor, however, do not show any significant wavelength specific changes. The integrated TSL output appears to be rate-dependent for both phosphors. The wavelength dependent changes in TSL output observed for CaSO₄:Eu phosphor have been correlated with those obtained in PL studies. The changes in TSL and PL characteristics of CaF₂:Tb³⁺ phosphor have been explained on the basis of stabilisation of traps based on matrix specific charge similarities.     

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.     

Preparation and characterization of tunable YVO4: Bi, Sm phosphors

Yttrium vanadate phosphors co-doped with Bi³⁺- and Sm³⁺ ions have been prepared via the solid-state reaction as well as via the sol-gel method. The luminescence studies demonstrate the potential of the prepared phosphors as multi-color emitters, which can be achieved by adjusting the excitation wavelengths. The excitation spectra of Bi³⁺- and Sm³⁺ co-doped phosphors clearly revealed energy transfer from Bi³⁺ to Sm³⁺ ions. When the co-doped phosphors were excited at 254 nm, the emission from Bi³⁺ was dominant. Upon excitation at 365 nm, the emission from both Bi³⁺ and Sm³⁺ was detected. With 410 nm excitation, Sm³⁺ ions were selectively excited to yield intense red emission. It is shown that the prepared phosphors with optimal concentrations of Bi³⁺ and Sm³⁺ can be excited at 254, 365 and 410 nm to yield yellow, orange and red emissions, respectively.     

Synthesis and luminescence of SrZnO2 phosphors

SrZnO₂ phosphors have been synthesized by two new methods viz. carbonate decomposition at 1000 °C and combustion synthesis. Phosphors activated with Pb²⁺, Sm³⁺, Tb³⁺, Bi³⁺ and Pr³⁺ could be prepared in one step using the combustion synthesis. Characteristic emission and excitation were observed for Bi³⁺. For the remaining activators excitation spectra always contained a band at 283 nm. Presence of this band for all these different types of activators was interpreted as host sensitization.     

Synthesis, structure and luminescence properties of Y(V,P)O4:Eu,Bi phosphors

YVO₄:Eu³⁺-based red-emitting phosphors with the compositions of Y_0.95−xVO₄:0.05Eu³⁺,xBi³⁺ (x=0.01, 0.03, 0.05, 0.07 and 0.09) and Y_0.90(V_1−zP_z)O₄:0.05Eu³⁺,0.05Bi³⁺ (z=0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were synthesized by the high temperature solid-state method. The as-prepared phosphors have the similar tetragonal phase structure and their morphologies varied with the relative content ratio of V to P. The photoluminescence spectra for the as-synthesized phosphors show that a dominant red emission line at around 619 nm, which is due to the Eu³⁺ electric dipole transition of ⁵D₀-⁷F₂, is observed under different excitation wavelengths (254 and 365 nm). Further, the emission intensities of ⁵D₀-⁷F₂ transition upon 365 nm excitation increase sharply owing to the Bi³⁺ doping. Energy transfer process, luminescent lifetime and quantum efficiency for the selected Y_0.90(V_1−yP_y)O₄:0.05Eu³⁺,xBi³⁺phosphors were also studied in detail.