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

The energy transfer (ET) between Tb3+ and Eu3+ is investigated experimentally and with available theoretical models in the regime of high Tb3+ concentrations in approximate to 30 nm LaPO4 nanoparticles at room temperature. The ET efficiency approaches 100% even for lightly Eu3+-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 Tb3+ ions, situated on La3+ sites with approximate to 4 angstrom separation, is not fast. The quenching of Tb3+ emission in singly doped LaPO4 only reduces the luminescence lifetime by approximate to 50% in heavily doped samples. Various theoretical models are applied to simulate the luminescence decays of Tb3+ and Tb3+, Eu3+-doped LaPO4 samples of various concentrations and the transfer mechanism is identified as forced electric dipole at each ion.