The emission spectrum of neat Sr 3 Tb(PO 4 ) 3 upon excitation at 337nm in the levels above 5 D 3 is dominated by 5 D 4 emission and no significant emission from 5 D 3 is observed due to efficient cross relaxation involving the Tb 3+ levels. On the other hand, the emission spectrum of the same host containing 10mol% Eu 3+ upon excitation at the same wavelength (in the Tb 3+ levels) is dominated by strong emission bands from the 5 D 0 level of Eu 3+ . This clearly indicates that Tb 3+ →Eu 3+ energy transfer is present. The excitation spectrum of the Eu 3+ 5 D 0 emission is dominated by Tb 3+ bands extending in the UV region.The presence of 10mol% Eu 3+ in Sr 3 Tb(PO 4 ) 3 very strongly shortens the 5 D 4 decay time. The decay curve is not far from exponential, indicating that the energy transfer to Eu 3+ is accompanied by fast energy migration. The transfer regimes are identified and the donor–donor and donor–acceptor transfer microparameters are quantified under the assumption of electric dipole–electric dipole interactions.