LUMINESCENCE OF GdF3:Pr:Yb AND YF3:Pr:Yb SOLID SOLUTIONS SYNTHESIZED BY CRYSTALLIZATION FROM THE MELT

Abstract

Spectral-luminescent characteristics of solid solutions GdF₃:Pr:Yb and YF₃:Pr:Yb synthesized by the crystallization from the melt are investigated. Down-conversion luminescence of the Yb³⁺ ions in the region of ²F_5/2 → ²F_7/2 transitions at 445 nm excitation was studied. Energy transfer coefficient from Pr³⁺ to Yb³⁺ ions was <80% for the ratio of Pr/Yb concentrations 0.5/10.0 and 1.0/10.0 for GdF₃, and 0.5/10.0 for YF₃. High efficiency of nonradiative energy transfer does not lead to high values of absolute quantum yield of luminescence of Pr³⁺ and Yb³⁺ ions in the region of maximum photosensitivity of crystalline silicon. The quantum yield does not exceed 1 % for the intrinsic luminescence Yb³⁺ and 4 % of the total luminescence in the range 800—1050 nm (for the ratio of Pr/Yb concentrations 0.5/1.0 in the GdF₃ matrix). The low quantum yield is a consequence of the complex pattern of energy exchange between ions Yb³⁺ and Pr³⁺, which is largely influenced by the energy proximity of the ¹G₄ state of the ion Pr³⁺ and ²F_5/2 of the ion Yb³⁺ in these matrices and by the cross-relaxation between the transitions ³P₀ → ¹G₄ of the ion Pr³⁺ and ²F_5/2 → ²F_7/2 of the ion Yb³⁺. The energy proximity results in an additional channel of non-radiative decay of the excited state of the ions Yb³⁺, and the cross-relaxation leads to an increase in the lifetime of the ³P₀ state of the ion Pr³⁺.