Luminescence from the Pr 4f5d and S0 states in LiLaP4O12

The photoluminescence and excitation spectra of Pr³⁺ activated LiLaP₄O₁₂ has been investigated in the 10-300 K temperature region. At all temperatures, the luminescence consists of optical transitions emanating from both the Pr³⁺ 4f¹5d¹ and the ¹S₀ states. However, at low temperatures the emission spectrum is dominated by the intraconfiguration emission transitions emanating from the Pr³⁺¹S₀ state. With increasing temperature, there is an exchange of intensity between the two emitting states; emission transitions from the ¹S₀ state exhibit strong intensity quenching while the 4f¹5d¹→4f² emission transitions reveal intensity gain. These results are explained on the basis of thermal population of the 4f¹5d¹ state by the ¹S₀ state. The energy barrier of 0.05 eV (403 cm⁻¹) for the nonradiative process is determined from the temperature dependence of the ¹S₀ lifetime.