Energy Transfer between Tb 3+ and Eu 3+ in LaPO 4 : Pulsed versus Switched-off Continuous Wave Excitation

Abstract

The energy transfer (ET) between Tb 3+ and Eu 3+ is investigated experimentally and with available theoretical models in the regime of high Tb 3+ concentrations in ≈30 nm LaPO 4 nanoparticles at room temperature. The ET efficiency approaches 100% even for lightly Eu 3+ -doped materials. The major conclusion from the use of pulsed laser excitation and switched-off continuous wave laser diode excitation is that the energy migration between Tb 3+ ions, situated on La 3+ sites with ≈4 Å separation, is not fast. The quenching of Tb 3+ emission in singly doped LaPO 4 only reduces the luminescence lifetime by ≈50% in heavily doped samples. Various theoretical models are applied to simulate the luminescence decays of Tb 3+ and Tb 3+ , Eu 3+ -doped LaPO 4 samples of various concentrations and the transfer mechanism is identified as forced electric dipole at each ion.