Temperature Dependences of Mn 2+ Photoluminescence with Different Local Surroundings in ZnS Single Crystals
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Journal of Applied Spectroscopy, Vol. 87, No. 4, September, 2020 (Russian Original Vol. 87, No. 4, July–August, 2020)
TEMPERATURE DEPENDENCES OF Mn2+ PHOTOLUMINESCENCE WITH DIFFERENT LOCAL SURROUNDINGS IN ZnS SINGLE CRYSTALS T. A. Prokofiev* and A. V. Ivanchenko
UDC 535.37;548.0
Photoluminescence spectra of Mn2+ in ZnS single crystals were recorded in the range 77–623 K at different activator concentrations and exciting radiation wavelengths. Spectra were decomposed into individual bands, each of which corresponded to radiation of manganese centers with a certain type of local symmetry. The obtained results made it possible to estimate the effect of activator concentration and temperature on changes in the number of radiating manganese centers with different types of local symmetry relative to all luminescent Mn2+ in ZnS single crystals with different excitation wavelengths. The results are explained in terms of the redistribution of direct optical and resonant mechanisms of energy transfer of the exciting light to Mn2+ taking into account losses due to nonradiative interaction with the ZnS single-crystal lattice. Keywords: photoluminescence, energy transfer mechanism of exciting light, temperature dependence of Mn2+ in ZnS single crystals, decomposition of luminescence spectra into individual bands. Introduction. The photoluminescence (PL) spectrum of ZnS single crystals doped with Mn2+ is inhomogeneous and consists of several overlapping individual bands. Each PL band is associated with emission of manganese centers (MC) with a certain type of local surroundings in the ZnS crystal lattice [1–6]. For example, the individual PL band with λmax = 557 nm is associated with emission of Mn2+ located in packing defects with C3v point symmetry (AS- and PN-type sites) and in a field with cubic point symmetry Td (AN-type sites) [1–3]. The individual band with λmax = 578 nm is attributed to emission of MC located near dislocations and point defects [1, 4]. The band with λmax = 600 nm corresponds to emission of MC located in a cubic environment in octahedral interstices [1, 4, 5]. The individual band with λmax = 635 nm is related to emission of an α-MnS phase interspersed in ZnS [6]. According to classical concepts [7], a temperature change affects the interaction of neighboring atoms in a crystal lattice and enhances or weakens the interaction of MC with their local surroundings. As a result, the probabilities of radiative transitions of Mn2+ located at different sites of the ZnS single-crystal lattice vary. Consequently, changes are observed in both the total number of MC contributing to the PL and the quantitative ratios between MC associated with emissions of various individual PL bands that alter the PL spectrum of the studied single crystals. Temperature dependences of individual PL bands are studied because the integrated intensity (area under the curve) of each individual PL band is proportional to the number of MC associated with it [8]. This allows changes of emitting MC with different local surroundings to be st
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