Upconversion dynamics in Pr-doped YAlO3 and Y3Al5O12 laser crystals

The praseodymium ion in solids exhibits emission from a number of levels located in different regions of the spectrum and presents various spectral features that include anti-Stokes emission, otherwise called upconversion. We have examined this phenomenon in two laser crystals YAlO3 and Y3Al5O12 doped with praseodymium. We studied the dynamics of the upconversion of the exciting energy by measuring decay patterns and emission intensities as function of excitation and temperature in the range 24-300 K. The experimental data indicate that the mechanisms responsible for the upconverted emission are energy transfer in YAlO3 and excited state absorption in Y3Al5O12. The mechanism of upconversion for each system persists at all temperatures. We observed upconverted emission in both samples when exciting the system in the 1D2 level with light from a dye laser at ∼599 nm. In YAlO3:Pr this emission is due to transitions originating in 3P0, a level more energetic than the 1D2 level. We found the intensity of this emission to be proportional to the square of the intensity of the excitation energy. In Y3Al5O12:Pr we observed upconverted emissions originating in the 3P0 level and in the (4f5d) band. We found the former emission to be proportional to the square of the excitation energy, and the latter to the cube of this energy.