Luminescence of fluctuation tails of disordered solid solutions

The form of the stationary luminescence spectra of excitons, localized by composition fluctuations, in disordered solid solutions under weak excitation is calculated. The tail states for which there are no nonradiative transition channels are distinguished by means of continuum percolation theory. Such states are responsible for the “zero-phonon” luminescence band. The shape of the short-wavelength luminescence band edge is determined mainly by the number of isolated localizing clusters and their smallest complexes, which decreases rapidly near the mobility threshold. The real luminescence spectrum is due to the simultaneous emission of phonons. The phonon emission determines the form of the long-wavelength wing of the emission band. The computed shape of the emission spectrum is compared with the experimental luminescence spectra of the solid solution CdS_(1−c)Se_c. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 3, 274–279 (10 February 1997)     

Luminescence spectra of solid xenon excited by volume discharge

The luminescence spectra of solid xenon excited by a volume discharge are studied for the first time. The majority of the energy is emitted in the VUV spectral region due to the radiative decay of excitons. A specific feature of the spectra in the UV and visible regions is the complete absence of lines belonging to neutral excited particles (one-center Xe* and two-center Xe ₂ ^* excitons) and to diatomic Xe ₂ ⁺ ions. Numerous lines of the Xe⁺ ion are shifted by 0.1–0.3 nm with respect to their positions in the gas; the larger the shift, the stronger the distortion of the line shape. Based on the data obtained, a mechanism by which solid xenon is excited and ionized by fast drifting electrons is proposed.     

Luminescence properties of solid solutions of borates doped with rare-earth ions

The structural and luminescence properties of Lu _x Y_{1 ? x} BO₃ solid solutions doped with Ce³⁺ or Eu⁺³ have been investigated. It has been found that the solid solutions crystallize in the vaterite phase with a lutetium concentration x < 0.5. For a higher lutetium concentration x, the solid solutions contain an additional calcite phase with a content less than 5 wt %. The luminescence spectra are characterized by intensive impurity emission under excitation with the synchrotron radiation in the X-ray and ultraviolet spectral ranges. It has been shown that, as the lutetium concentration x in the Lu _x Y_{1 ? x} BO₃: Ce³⁺ solid solutions increases, the emission intensity smoothly decreases, which is associated with a gradual shift of the Ce³⁺ 5d(1) level toward the bottom of the conduction band, as well as with a decrease in the band gap. It has been established that, in the Lu _x Y_{1 ? x} BO₃: Eu³⁺ solid solutions with intermediate concentrations x, the efficiency of energy transfer to luminescence centers increases. This effect is explained by the limited spatial separation of electrons and holes in the solid solutions. It has been demonstrated that the calcite phase adversely affects the luminescence properties of the solid solutions.     

Luminescence of poly(N-vinylcarbazole) in the solution and solid state

Fluorescence spectra of poly(N-vinylcarbazole) have been studied as a function of various environments and temperature. Fluorescence spectra have been excited with UV light from 200 W Xenon lamp or with second-harmonics of a pulsed ruby laser. Polymer films and powders show exclusively excimer fluorescence at room temperature. At high intensities of excitation the observed fluorescence spectra have a weak quasiperiodic structure.     

Luminescence of Pr3+ ions in Y3Al5−xGaxO12 solid solutions

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 5, pp. 774–778, November, 1991.     

Luminescence kinetics characteristics of lead-containing aggregates dispersed in Rb0.95Cs0.05Cl solid state solution

The relaxation of the electron excitations in an insulating matrix such as the Rb_0.95Cs_0.05Cl solid solution containing CsPbCl₃ nanocrystals and single lead centers is studied. Modification of the spectral kinetic parameters of the CsPbCl₃ nanocrystals due to the quantum confinement is explored. Mechanism of the energy transfer from matrix to the nanocrystals is established. The luminescence of the Rb_0.95Cs_0.05C–Pb crystal is characterised by means of measurements with subnanosecond time resolution under synchrotron radiation excitation in the energy range of 3.7–20 eV at T=10 K.     

Luminescence kinetics of an Y0.8Yb0.2F3:Tm3+ solid solution crystal

Upconversion luminescence kinetics of Tm³⁺ doped Y_0.8Yb_0.2F₃ solid solution crystal was studied for various values of pulse excitation parameters: pulse duration, wavelength and excitation power. Analysis of obtained results allowed a conclusion about the presence of transient processes. The transient processes found in upconversion luminescence kinetics are characterized by duration commensurate with lifetime of the excited energy levels of the activator ions. Upon completion of these processes a stable equilibrium state is established between the processes of population and spontaneous decay of the excited energy levels of Tm³⁺ ions. Conditions under which the equilibrium state can be maintained have been considered.     

Luminescence problems

The article deals with the interpretation of the experimental results on luminescence and on the degree to which this interpretation is unambiguous and noncontradictory. More than 30 concrete cases are considered and are used as examples to demonstrate that if the experimental conditions that are seemingly of secondary importance are not sufficiently well accounted for the experimental results themselves may turn out to be ambiguous. The particular experimental conditions that can be especially “insidious” in this respect are indicated. The examples concern the kinetics of the luminescence and the investigations of its spectra and polarization.     

Luminescence of poly-N-epoxypropylcarbazole

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 1, pp. 41–49, July, 1990.     

利用离子激发发光研究低温条件下ZnO发光行为EI北大核心CSCD

离子激发发光(Ions beam induced luminescence,IBIL)可以实时原位分析不同温度、不同离子辐照条件下材料内部点缺陷的演变行为。本文利用2 MeV H^(+)研究了300,200,100 K温度下ZnO单晶内部点缺陷发光及其随注量的演变行为。实验中发现ZnO深能级发射和近带边发射,结合Voigt分峰与XPS实验结果,确定红光(1.75 eV)与V_(Zn)相关,橙红光(1.95 eV)来自Zn_(i)到O_(i)跃迁;对于与V_(O)相关的绿光(2.10 eV),其红移可能由于温度降低导致更多电子由导带释放到Zn_(i)。峰中心位于3.10 eV和3.20 eV近带边发射分别来自于Zn_(i)到价带的跃迁和激子复合,红移原因分别为Zn_(i)附近局域化能级和带隙收缩。利用单指数公式对发光强度进行拟合,获得的衰减速率常数(f)可以表征缺陷的辐射硬度,对比发现深能级发射峰在200 K时辐射硬度最大,而近带边发射峰在300 K时辐射硬度最大。     

Luminescence of Leuco-Thiazine Dyes

Details of the novel luminescence of the leuco forms of the thiazine dyes, methylene blue and thionine, are reported, including their emission maxima, quantum yields and lifetimes of the luminescence. Other work shows that this luminescence is independent of reducing agent type and solution pH and is a common feature of most thiazine dyes.     

Luminescence of silver chlorides

It was found that single crystals of silver chloride without admixtures, prepared in the Institute of Physics of Charles University, exhibit a luminescent colour change at the temperature of liquid air. According to the change in luminescence the crystals can be divided into three groups —those with predominant red-orange, green-blue and blue-green luminescence.This paper briefly describes the factors influencing the colour changes in the luminescence of silver chloride. More details on the experiments and the connection between the changes in luminescence and the absorption will be given later.In conclusion the author thanks R. Kiradjieffová for her great help in the work.     

闪烁晶体的发光研究进展

概述了近年来闪烁体发光研究的进展,主要介绍用于未来高能物理实验的新型闪烁体发光机理研究,选取我们在研BaF₂,BaF₂:RE,CeF₃以及PbWO₄中的一些新进展。重点谈及三点:(1)在BaF₂的“价带^→芯带”跃迁发光研究基础上进行稀土(Gd³⁺-Eu³⁺)掺杂时观察到的量子剪裁以及对多光子发光的新思考;(2)CeF₃晶体发光的级联能量传递中,Ce³⁺(290nm发射带)与缺陷发光中心(340nm发射带)间能量传递及其传递效率的温度依赖;(3)PbWO₄晶体的发光中心研究中,提出以“WO₄^-2+O_i”绿光中心替代“WO³+F”中心观点的依据。同时也简介了医用闪烁体的最新进展。     

Luminescence of acetylated cellulose

Several luminescence properties of acetylated cellulose were studied as functions of the ester group concentration and of the wavelength of the exciting radiation. Of the three luminescence bands arising on irradiation at specific wavelengths, the ultraviolet band has a structure. A correlation was established between the intensity of this band and the ester group content, as well as a qualitative similarity between the luminescence excitation spectra and the absorption spectra. The relative quantum yield of the luminescence depends on the wavelength of the excited radiation. It is proposed that the centers which are specific for the ultraviolet luminescence are acetyl groups of two different types.