Influence of Impurities on the Luminescence Quantum Efficiency of ( La , Ce , Tb ) PO 4

The influence of impurities on the luminescence quantum efficiency of and has been studied. The transition metal ions Fe and Mn are not built into the lattice under a reducing firing atmosphere. Tetravalent Ce4+ is probably present in a second phase. Codoping with cations with different valencies has no influence on the Ce4+ amount nor on the Ce3+ quantum efficiency. The energy transfer rate from Ce3+ to a number of rare‐earth ions (Pr3+, Nd3+, Dy3+, Ho3+, Er3+) is low. Therefore, low concentrations of these ions do not compete efficiently with the Tb3+ ion for the excitation energy on the Ce3+ ion. However, the Ce3+ quantum efficiency is reduced by Eu3+ due to an electron transfer process. Energy transfer between Tb3+ ions is restricted to Tb3+ clusters, so that the probability that the excitation energy reaches impurities is low. Therefore low concentrations of rare‐earth ions have only a small effect on the Tb3+ quantum efficiency.