Up-conversion and excitation energy transfer between impurity ions in Pr3+ : Y2SiO5, Pr3+ : Lu2SiO5, and Pr3+ : Gd2SiO5 crystals

Anti-Stokes fluorescence from the ³P₀ level of impurity ions was detected in Pr³⁺ : Y₂SiO₅, Pr³⁺ : Lu₂SiO₅, and Pr³⁺ : Gd₂SiO₅ crystals non-resonantly pumped by laser radiation with a certain power density. The integrated intensity of the anti-Stokes fluorescence depends nonlinearly on the pump power density. As the atomic concentration of impurity ions was increased from 0.3% to 0.6% and 1.8%, the anti-Stokes fluorescence intensity was saturated due to the concentration quenching of the ¹D₂ term of the impurity Pr³⁺ ions. The anti-Stokes fluorescence and quenching of the ¹D₂ term occur due to the cross relaxation of the electronic energy of excited terms of the Pr³⁺ ions.