Induced superradiance in activated crystals

The observation of superradiance in activated crystals induced by propagation of a short coherent pulse through an inverted sample is proposed. The theoretical estimation of the induced superradiance in Nd: YAG is given.     

Migration transfer of electronic excitation energy in activated solids

An analytic expression for the kinetics of quenching of donor luminescence in the presence of acceptors with allowance for migration of energy over the donor subsystem is derived. An extended criterion for the applicability of the hopping migration model is obtained.     

Luminescence and electronic excitation energy migration in stilbene crystals

Absorption and luminescence spectra are reported for various conditions. A new band occurs at the short-wave edge of the luminescence spectrum above 90 ° K, which probably represents the short-wave component of the exciton radiation. Reabsorption has a marked effect on the energy distribution in the luminescence spectrum.     

Indirect optical cooperative excitation of two-particle electronic excitations in doped organic molecular crystals

A theory on the indirect optical cooperative excitation of a two-particle electronic excitation composed of one host exciton and one guest-molecule one-particle electronic excitation through one electric dipole-moment active singlet guest molecule one-particle electronic excitation is developed by considering the nonradiative coupling bstween one- and two-particle electronic excitations.The complex dielectric tensor and the corresponding absorption coefficient are found out, which are expressed in terms of the Fourier-transform of the retarded Green function: The derived formulas are discussed in an explicit form for the one-dimensional model of the doped organic molecular crystal. Within the framework of ths one-dimensional model also the conditions for the existence of the host exciton-guest molecule one-particle electronic excitation bound states are established and discussed.     

Neutral particle emission from zinc oxide surface induced by high-density electronic excitation

Emission of neutral zinc and oxygen atoms and oxygen molecules emitted from zinc oxide surface by laser irradiation have been measured. It is found that the emission intensity starts to increase when the laser intensity exceeds a certain threshold value, indicating that the particle emission is a high density electronic excitation effect. The energy spectrum of emitted particles is found not to follow the Maxwellian distribution.     

The temperature dependence of the edge emission of GaSe single crystals at high excitation levels

The temperature dependence of five edge emission lines of GaSe at high excitation levels has been investigated by using the second harmonic of a neodymium-glass laser. The following lines were indentified at 77.3K:hv_B = 2.102 ± 0.002 eV, annihilation of free excitons; hv_C = 2.082 ± 0.003 eV, Auger recombination of free excitons; hv_D = 2.072 ± 0.003 eV and hv_E = 2.055 ± 0.004 eV, annihilation of free excitons with emission of optical phonons (LO₁ = 31 meVandLO₂ = 45 meV, respectively); hv_G = 2.036 ± 0.004 eV, radiative recombination at indirect transition with emission of LO₁ phonons.     

Luminescence of double-fluoride crystals activated with thallium

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 3, pp. 375–380, September, 1990.     

Kinetics of electronic excitation decay in LiNbO<Subscript>3</Subscript> crystals

A model for calculation of kinetic characteristics of electronic excitation decay in the impurity subsystem of doped crystals with taking into account the phenomenon of excitation trapping is suggested. Numerical calculations are carried out for LiNbO₃:Yb³⁺ crystals: the probabilities of elementary acts of resonant and non-resonant nonradiative redistributions of electronic excitation energy in the impurity subsystem are calculated and the dependences of excitation lifetime and luminescence quantum yield on the concentration of pair centers in the matrix of LiNbO₃ crystals are determined.     

Anisotropy of x-ray emission spectra and electronic structure of V2O5 single crystals

The results of investigation of x-rayVK- andVL-emission spectra orientation dependence for V₂O₅-single crystals are reported. The applicability of different options of electronic structure cluster calculations for the interpretation of x-rayVK-emission bands anisotropy in V₂O₅-single crystal is discussed.     

Ultraviolet excitation of rare-earth-doped YSZ crystals

Abstract

The optical properties of nominally pure and Er³⁺- or Pr³⁺ -doped yttria-stabilized zirconia single crystals were investigated under UV light excitation. In the excitation spectra of both types of doped crystals, a broad UV band is observed. Under excitation with light of different wavelengths inside this band, the luminescence features of the doped crystals are different. YSZ: Pr³⁺ samples exhibit the characteristic 4f → 4f emission of the Pr³⁺ ions. In YSZ: Er³⁺ crystals, both the Er³⁺ ion and the intrinsic luminescence are observed. Host to Er³⁺ ion radiative energy-transfer is also demonstrated. No dependence of the transfer process with the excitation wavelength was found. These results suggest that the UV band in Er³⁺ -doped crystals is associated with the lattice-dopant ion interaction rather than with the 4f5d interconfigurational band of the Er^3? ions.     

Electroluminescence of alkali halide crystals activated with europium ions

The prebreakdown electroluminescence of NaCl-Eu, KCl-Eu, and KBr-Eu crystals has been studied. The activator concentration in the crystals was on the order of 10¹⁸ ions per cubic centimeter. The emission spectra, the brightness wave during pulsed excitation, and the concentration dependence of the quantum yield were measured. The experimental results support the suggestion of an impact mechanism for the excitation of the electroluminescence of alkali halide crystals. Recombination and exciton mechanisms for energy migration play an insignificant role. There is no significant contribution from impurity-vacancy dipoles, which act as emission centers, in electric fields up to 10⁶ V/cm.Tomsk Academy of Control and Electronic Systems. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 105–109, February, 1994.