Tb3+→Ce3+Tb3+→Ce3+ energy transfer in Y3-x-yTbyGdxAl5O12Y3-x-yTbyGdxAl5O12 (x=0.65x=0.65, y=0.575y=0.575) doped with Ce3+Ce3+

Photoluminescence and luminescence excitation spectra of Y2.3-xTbxCe0.05Gd0.65Al5O12Y2.3-xTbxCe0.05Gd0.65Al5O12 (x=0.575x=0.575) have been measured at room temperature. Depending on the excitation wavelength the broad band emission related to interconfigurational transitions in Ce3+Ce3+ ions, or the sharp lines luminescence related to D45→F67, D45→F57, D45→F47 and D45→F37, transitions in Tb3+Tb3+ ions have been observed. It has been found that efficiency of Tb3+→Ce3+Tb3+→Ce3+ energy transfer depends on the excitation energy, specifically it is less effective when Tb3+Tb3+ is excited to the lowest state of the excited 5d14f75d14f7 electronic configuration. This effect has been tentatively attributed to the nonradiative de-excitation of Tb3+Tb3+ ion to the metastable 5D45D4 state. Configurational model has been developed, which explains the peculiarities of relaxation in the excited states of Tb3+Tb3+ and Ce3+Ce3+, and Tb3+→Ce3+Tb3+→Ce3+ energy transfer.