Luminescence of the vanadate group in phosphovanadates with general formula RbCaLa(PO4)2-x(VO4)x (0<x≤2)

These phospho-vanadates crystallize with a structure similar to that of hexagonal LnPO4, except that the Rb atom occupies the large tunnel of this lattice and the Ca and Ln atoms are statistically distributed in the Ln position. These materials exhibit a strong yellow-green broad-band luminescence, even at room temperature. Both excitation and emission take place in the vanadate groups. The excitation band is attributed to the 1A1 →1T1 (1t1→2e) transition and the emission is assumed to originate from the (3T1, 3T2) triplets. Spectroscopic investigations at low temperature show the vibronic character of the emission. A three-levels model is used to interpret the thermal evolution of the emitting level lifetimes