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2The 30th International Conference on Advanced Laser Technologies ALT'23
LS-P-3
Changes in the structure and functional parameters of the CVO optical medium doped with chromium
L.I.Ivleva1, G.M.Kuzmicheva2, M.E.Doroshenko1
1-Prokhorov General Physics Institute, Russian Academy of Sciences, Vavilov str.38, Moscow, 119991, Russia 2- MIREA - Russian Technological University, 78 Vernadskogo pr., Moscow, 119454, Russia
Calcium orthovanadate Ca3(VO4)2 (CVO) is an optical material whose properties are defined by disordered whitlockite-like structure without an inversion center (sp.gr. R3c). Based on the structural features the crystal-chemical composition of stoichiometric CVO can be described as [Ca1i8Ca2i8Ca3i8Ca46(Ca5+Ca5A)3](V1i8V2i8V36)Oi68, indicating the multiplicity of crystallographic sites. A change in the functional parameters of the optical medium is preceded by a change in the structure of the crystalline matrix, caused by the introduction of dopant ions. X-ray diffraction analysis and optical spectroscopy were used to study structural and spectroscopic parameters, actual composition, and point defects in CVO:Cr.
It was shown that chromium ions in various valence states can substitute Ca2+ ions in different positions (Ca2, Ca3,Ca4) with appropriate excessive charge compensation formation vacancies in V-sites. Locations of Cr ions in the matrix and cell parameters were depended on Cr concentration. Real crystal compositions in the form of (Ca,Cr)[(V 5+,r)C>4]2 (1- vacancies) were defined with Cr3+ ions with octahedral coordination for green colored crystals and Cr 4+ ions with tetrahedral coordination for yellowish CVO:Cr.
Absorption spectra of chromium ions in CVO crystal and fluorescence measurements were carried out in visible and near IR spectral range. Absorption bands with maxima about 600, 700 nm and above ii00 nm were observed for investigated crystals. Time resolved excitation and fluorescence spectra measured for CVO:Cr crystal as-grown and after annealing were analyzed. In CVO:Cr (0.05 at%) as grown crystal the presence of Cr3+, Cr4+ and Cr5+ ions was revealed. Annealing of the Ca3(VO4)2:Cr crystal in the air was observed to result in an increase of chromium ions in 4+ and a decrease in 3+ valence state. This should obviously originate from sufficient decrease of Cr5+ ions amount which concentration looks to be nearly negligible in annealed sample. Some Cr5+ to Cr3+ ions charge exchange process (Cr5+^Cr4++e-; Cr3+ +e-^Cr4+) resulting in formation of two Cr4+ ions may take place which decrease both Cr5+ and Cr3+ ions concentration in the annealed sample. As a result, crystalline materials activated by chromium ions are very promising for laser media and are intensively studied at present.
The work was supported by Ministry of Science and Higher Education: grant № 075-i5-202i-i362.
