Energy transfer of intrinsic electronic excitation to impurities in the CaSO4 − Mn crystal

The nature of the impurity emission center and the energy transfer mechanisms from intrinsic electronic excitations to the Mn2+ impurity centers in the CaSO4 − Mn crystal have been investigated. The methods of vacuum ultraviolet, atomic absorption and luminescence spectroscopy are used in a wide temperature range from 5 K to 300 K. The energy transfer of intrinsic electronic excitations to impurity emission centers in CaSO4 − Mn has been detected.

Фононный спектр и упругие свойства Y-=SUB=-2-=/SUB=-Sn-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-

In the framework of a unified ab initio approach, the phonon spectrum of yttrium stannate Y2Sn2O7 was calculated, the frequencies and types of IR and Raman modes were determined. From an analysis of the displacement vectors obtained in ab initio calculations, the degree of participation of ions in phonon modes is determined. The elastic constants and hardness of Y2Sn2O7 are calculated. The distance "impurity ion-ligand" in impurity centers Y2Sn2O7: Yb3 +, Y2Sn2O7: Eu3 +, Lu2Sn2O7: Yb3 +, Nd2Sn2O7: Gd3 +, Nd2Sn2O7: Tb3 + is calculated.

Электрополевой эффект в спектрах ЭПР центров Fe-=SUP=-3+-=/SUP=- и Mn-=SUP=-4+-=/SUP=- в тонких пластинках SrTiO-=SUB=-3-=/SUB=-

The results of the study of the electric field effect in the electron paramagnetic resonance spectra of the Fe3+ and Mn4+ impurity ions in thin oriented strontium titanate single-crystal plates are presented. The crystal structure of plates at T> 105 K turned out to be tetragonal, different from both the cubic and the antiferrodistortive tetragonal, inherent to SrTiO3 at T < 105 K. It is shown that for the studied centers, the electric field effect is quadratic in the applied electric field and has the same sign and order of magnitude, indicating the nonpolar origin of the observed high temperature tetragonal state. Analysis of the dependences of the axiality value on the applied field indicates that the electric field effect does not originate from the electrostriction and is due to the modification the wavefunction of the ground state of the impurity centers.

THE INFLUENCE OF THE MOVEMENT OF IMPURITY IONS ON THE STABILITY OF LEDS

The influence of the motion of impurity centers on the stability of GaInAsP-based light- emitting diodes and their efficiency are studied. The stability and efficiency of the electroluminescence of LEDs is mainly determined by the ratio between the intensities of the radiative and non-radiative recombination of charge carriers. We studied the electroluminescent and electrical characteristics of LEDs. To clarify the degradation mechanism of LEDs, we studied the effect of their current training for 3000 hours at various current densities for stability and efficiency and for their electrical characteristics. It was shown that the degradation of LEDs at low injection levels is associated with the drift of impurity centers near the inhomogeneities of р-л-junctions. It is shown that during the degradation of LEDs, the magnitude of the radiative current component at a fixed voltage varies little. At the same time, nonradiative current components increase significantly. It was established that the growth of nonradiative current components is associated with the drift of mobile impurities to inhomogeneities of the р-л-junction. The kinetics of LED degradation was calculated using certain assumptions. The diffusion coefficient of the ions responsible for the degradation of the diodes is estimated. It is shown that “sudden” LED failures are of the same nature as their gradual degradation. They can occur at a sufficiently high concentration of mobile impurities. The obtained dependences of the radiation intensity on the duration of degradation can be used to estimate the diffusion coefficient of a mobile impurity.

Перенос заряда и центры F типа в щелочноземельных фторидах, активированных ионами Cd-=SUP=-2+-=/SUP=- или Zn-=SUP=-2+-=/SUP=-

The photoluminescence spectra of impurity centers containing the anionic vacancy Cd+va or Zn+va in alkaline-earth fluorides are studied. A comparison with the luminescence spectra of photochromic centers (РC), which can be considered as perturbed F centers, shows that the luminescence of the Cd+va or Zn+va centers is similar to the luminescence of F centers and, therefore, is associated with charge transfer from an impurity ion to an anionic vacancy.