Effect of impurities and disordering on the photoluminescence of crystals and glasses in the system Li2O - 7GeO2

The work is devoted to the study of photoluminescence spectra of weakly polar ferroelectric crystals Li2Ge7O15 and Li2O – 7GeO2 glasses. For all initial samples was observed the wide intensive luminescence band with maximum in the region of 525–550 nm. The spectral distribution of intensity and the position of the maximum of the band for a Li2Ge7O15 crystal depended on the excitation wavelength (λex=405 nm or 365nm were used). The spectral profile of the luminescence band was broadened in glass containing of 0.67% copper. The intensity of the luminescence band was decreased 6 times for glass doped with Cr3+ ions (0.01%) as compared with glass containing Cu2+ ions. The intense luminescence band of Cr3+ ions with λmax=659nm was appeared starting from 600. The assumption about the nature of the broad luminescence band observed in both nominally pure and doped glasses and crystals was made: the source of luminescence can be germanium - oxygen complexes [GeO4] and [GeO6] of the tetrahedral and octahedral configuration in the material structure.

CRYSTAL STRUCTURE AND LUMINESCENT PROPERTIES OF Sr2B2O5:Eu2+ BLUE PHOSPHORS

The Sr2B2O5:Eu2+ phosphor was synthesized by high-temperature solid state reaction. The crystal structure of Sr2B2O5:Eu2+ phosphor is monoclinic system with space group of P21/a(14). Due to Eu2+ ion doping, the lattice parameters and unit cell volume decreased. The luminescence spectrum is a broad luminescence band peaking at 468 nm and 478 nm, which corresponds to the transition of 5d-low energy state in Eu2 and Eu1 to the ground state. The excitation spectrum is at UV region less than 264 nm corresponding to the band gap transition of borate host. The low energy level of 5d-band locates 20921 cm-1, the band width is 1 eV. The electronegativity of O2- anions around Eu1 and Eu2 is 3.147 eV and 3.326 eV respectively, which determines the split of 5d energy level.

Crystal Structure and Optical Properties of 4-[4-(Dimethylamino)- styryl]-1-methyl-pyridinium Lead Tribromide

The title compound crystallizes in the centrosymmetric space group I2/a. When pumped by 458 and 1064 nm laser radiation the compound gives rise to a broad luminescence band at ca. 668 and 671 nm, respectively.

OPTICAL PROPERTIES OF ANATASE TiO2 UNDER THE HIGH PRESSURE

Optical absorption, luminescence and Raman spectra were measured for anatase TiO 2 under high pressures. The pressure dependence of Raman frequencies is determined. The absorption edge of anatase shifts to higher energy side with increasing pressure and the edge jumps abruptly to lower energy side on the phase transition. A broad luminescence band of anatase shifts also to higher energy side with increasing pressure. These experimental results reveal that the pressure-induced phase transition from anatase to high-pressure phase arises in the range of 4.0-4.6 GPa.

TIME-RESOLVED PHOTOLUMINESCENCE OF EXCITONS IN HgI2

The time-resolved photoluminescence (TRPL) of red HgI 2 single crystal has been measured to determine the carrier lifetimes and to reveal the energy relaxation of excitons. Sharp near-bandgap luminescence lines due to free and bound excitons are observed at 530 nm, and a broad luminescence band appears at 630 nm at low temperatures. TRPL experiments of the near-bandgap luminescence have revealed that the luminescence comprise fast (30 to 200 ps) and slow (100 to 400 ps) decay components, showing several relaxation processes in free and bound exciton annihilation. TRPL of the broad band at 630 nm has shown that the luminescence is ascribed to the radiative recombination of donor-acceptor (DA) pairs.

Low Temperature Photoluminescence and Photoinduced Current Spectroscopy on CdZnTe Grown by High-Pressure Bridgman Technique

Low temperature photoluminescence (PL), photoinduced current spectroscopy (PICTS) and thermoelectric effect spectroscopy (TEES) measurements have been carried out on several CdZnTe samples, taken from the same ingot, grown by the High Pressure Bridgman Technique. The PL bandgap edge luminescence allowed us to study the quality of the CdZnTe material. We have also determined the zinc segregation through the ingot. A broad luminescence band at lower energies was observed and correlated with PICTS results. The behavior of the defects through the ingot was studied by PICTS. Finally, these results are used to implement the resistivity model.