Thermal population of the 4f15d1 state in BaSO4:Pr3+ -: art. no. 075118

Temperature-dependent measurements of luminescent intensity and lifetimes of the 4f(2)[S-1(0)-->I-1(6)] and 4f(1)5d(1)-->4f(2) emission for BaSO4:Pr3+ were performed. It was found that the intensity of the 4f(1)5d(1) emission, relative to the 4f(2) emission, increases with higher temperature, and that the decay time of the S-1(0)-->I-1(6) emission decreases from 190 to 56 ns. From both intensity and decay-time measurements an energy barrier between the 4f(2)[S-1(0)] level and the first 4f(1)5d(1) state of about 0.04 eV was found. At T=10 K also 4f(1)5d(1)-->4f(2) emission can be observed, which has a decay time of 10 ns. Emission from the 4f(1)5d(1) state at low temperature is not thermally coupled with emission from the S-1(0) state, but originates directly (not via the S-1(0) level) from excitation in the 4f(1)5d(1) band. This emission can be excited efficiently when pumping on the low-energy side of the 4f(1)5d(1) excitation band. This phenomenon of direct 4f(1)5d(1)-->4f(2) emission is only visible at low temperature as at higher temperatures, it is obscured by the 4f(1)5d(1) emission originating from the thermal population of the 4f(1)5d(1) state from the S-1(0) level.