In this paper, we present a detailed study of the concentration and temperature dependences of the quantum efficiency of energy transfer between Ce3+ and Tb3+ in La1−x−yCexTbyPO4. The determination of the transfer quantum efficiency in terms of the donor luminescence lifetimes is critically compared with that in terms of the donor luminescence intensities. It is shown that for the latter determination it is important to take into account any overlap in the donor and acceptor absorption spectra in the excitation wavelength region. From the exponential behavior, the concentration, and thermal dependences of the donor luminescence decay, it is shown that the diffusion of donor excitation plays an important role in the energy transfer process.

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