ФОТОЛЮМИНЕСЦЕНЦИЯ КРИСТАЛЛИЧЕСКОГО И СТЕКЛООБРАЗНОГО ТИОГЕРМАНАТА СВИНЦА

Abstract

Приводятся результаты сравнительного исследования спектров излучательной рекомбинации и возбуждения фотолюминесценции, температурной зависимости фотолюминисценции, люкс-яркостных характеристик кристаллического и стеклообразного PbGeS3 в интервале температур 77–300 К. Для обеих фаз тиогерманата свинца установлено наличие широкой ИК-полосы излучения с большим стоксовским сдвигом, температурное гашение ФЛ, линейные люкс-яркостные характеристики, что указывает на однотипность собственных дефектов, создающих локализованные электронные состояния в глубине запрещенной зоны, контролирующие процессы излучательной и безызлучательной рекомбинации в упорядоченной и неупорядоченной фазах. Ключевые слова: тиогерманат свинца, фотолюминесценция, температурное гашение ФЛ, спектры возбуждения, люкс-яркостные характеристики.

Purpose: The interest to glasses Ge–Pb–S system is due to the opening possibilities of using them as a three-dimensional optical coating for active devices of integrated optics and multifunctional devices of semiconductor photonics, as well as electrophoto-graphic layers characterized by small value of the limit charging potentials and fast kinetics of dark half-decay. Methods: This paper presents the comparative study results of radiative recombination and photoluminescence excitation (PLE) spectra, temperature dependence of photoluminescence, lux-brightness characteristics (LBC) of crystalline (c-) and glassy (g-) PbGeS3 in the temperature range 77–300 K. Results: The PL spectra of ordered and disordered phases are qualitatively similar; they contain one intense broad radiation band, the energy position of its maximum at T = 77 K is hvmax = 1.04 eV for the crystal and it lies within 1.13–1.18 eV for the glass. The luminescence excitation spectrum is a bell-shaped curve with a maximum at the photon energy of 2.7 eV for the crystal and 2.26 eV for the glass, which are close to the band gap of ordered and disordered phases, it indicates on the band-type excitation character. The Stokse shift WS = EPLE – EPL for the crystal phase WSс = 1.65 eV is much larger than for the glassy phase WSg = 1.07 eV. Lux-brightness characteristics (LBC) have the linear character for both PbGeS3 phases. Only slight shift of the maximum in PL spectra into the high energy region is observed with the intensity excitation increasing. Linear LBCs along with the exponential decay of PL indicate to the monomolecular character of recombination in both phases. The similarity of PL and luminescence excitation spectra of c- and g-PbGeS3 as well as their comparison to the known results for c- and g-GeS2 (GeSе2) allow to conclude that the radiative processes in lead thiogermanate are determined primarily by the chemical nature of luminescence centers and poorly depend on the presence of long-range order, while the nonradiative processes are very sensitive to the structure disordering. Conclusion: For the first time, in the photoluminescence spectra of both PbGeS3 phases, a wide band with a Gaussian-shaped contour was detected, with the emission band for glassy samples shifted by 0.1 eV towards higher energies. The relatively large half-widths and the absence of the oscillatory structure of the luminescence bands indicate that in both phases a high heat release occurs, and the energy position of the band maxima in the emission spectra indicates the impurity nature of the luminescence and high stokes losses. Keywords: lead thiogermanate, photoluminescence, temperature quenching of PL, excitation spectra, lux-brightness characteristics.