Photon cascade emission of Pr3+ in LnBaB(9)O(16) (Ln = La, Y)

Under 216 nm UV-excitation, cascade emission of Pr3+ occurs from S-1(0) Sta te in LaBaB9O16:Pr3+ that converts a single UV photon of high energy into t wo visible photons. The observation of the cascade emission in this oxide m atrix is largely due to the weak crystal field on the lanthanum sites. The analysis of the vibrational coupling indicates that the radiative transitio n from the P-3(0) state is related to the low phonon frequency of the BO4 b erate groups bonded to the lanthanum atoms (h omega (max)similar to 850 cm( -1)). On the other hand, the cascade emission does not take place in a clos ely related material, YBaB9O16:Pr3+, which can be interpreted by the fact t hat the 4f5d levels are located below the S-1(0) level in this material.