Luminescence and Upconversion Dynamics of Praseodymium in LiLuF₄ Laser Crystals

Abstract

We have investigated the spectroscopic properties of Pr³⁺ ions in LiLuF₄ laser host doped with 0.5% Pr³⁺ ions as a function of temperature. We obtained the luminescence spectra by exciting selectively the sample at 439nm into the ³P₂ level and at 593nm into the ¹D₂ level. With excitation in the ³P₂ level we obtained emission only from the ³P₀ level but not from the ¹D₂ level at all temperatures between 24 and 300K. With excitation into the ¹D₂ level we observed the luminescence emitted by the same level and a strong blue up-conversion emission from the ³P₀level. We used the decay pattern inspection to assign spectral lines to specific radiative transitions and to study the dynamics of the excited ions in the crystal. Under direct excitation, the ¹D₂ decay curve is nonexponential at all temperatures, whereas the ³P₀ decay is exponential only at low temperatures. The experimental data indicate that the ³P₀ level is populated via upconversion due to mainly energy transfer.