Blue Up-conversion in LaCl₃: Pr³⁺, U³⁺

A strong blue emission of Pr³⁺ ion in LaCl 3:Pr³⁺, U³⁺ crystal was observed after direct excitation of U³⁺ ion by a red laser set at 615.4nm.The anti-Stokes fluorescence arises from the 3P₀ state （around 490 nm）.From the analysis of the dynamics and flux dependence of the induced fluorescence,conclude that the observed phenomenon occurs via the following mechanism:first,across-relaxation process which transfers energy from ⁴I_11/2 level of U³⁺ ion to the ³H₆ level of Pr³⁺ ion,then,the excited state absorption from there.