Luminescence of GdF3:Pr:Yb and YF3:Pr:Yb Solid Solutions Synthesized by Crystallization from the Melt

Spectral and luminescence characteristics of GdF3:Pr:Yb and YF3:Pr:Yb solid solutions synthesized by crystallization from the melt were investigated. Down-conversion luminescence of Yb3+ in the region of 2F5/2 → 2F7/2 transitions with 445-nm excitation was studied. The energy-transfer coefficient from Pr3+ to Yb3+ was <80% for concentration ratios Pr/Yb 0.5/10.0 and 1.0/10.0 for GdF3 and 0.5/10.0 for YF3. The absolute values of Pr3+ and Yb3+ luminescence quantum yields in the region of the greatest crystalline-silicon photosensitivity were low because of highly efficient nonradiative energy transfer. The quantum yield was <1% for Yb3+ intrinsic luminescence and <4% for total luminescence in the range 800–1050 nm (for concentration ratio Pr/Yb = 0.5/1.0 in GdF3 matrix). The low quantum yield was a consequence of the complex energy-exchange pattern between Yb3+ and Pr3+ ions, which was largely influenced by the proximity of 1G4 and 2F5/2 energy states of Pr3+ and Yb3+, respectively, in these matrices. This opened an additional pathway for nonradiative decay of Yb3+ excited states and enabled cross-relaxation between 3P0 → 1G4 transitions of Pr3+ and 2F5/2 → 2F7/2 transitions of Yb3+ that increased the lifetime of the Pr3+ 3P0 state.