energy transfer in Ce3+-doped Y3−xTbxGd0.65Al5O12

Photoluminescence of Y2.3−xTbxCe0.05Gd0.65Al5O12 (x = 0.575, 1.15, 1.725 and 2.3) has been measured at room temperature at high hydrostatic pressure. Under excitation at 457 nm, the broad band emission related to interconfigurational transition from the lowest state of excited electronic configurations 5d1 to the ground state split by spin–orbit interaction into 2F5/2 and 2F7/2 components of Ce3+ ions, peaked at 550 nm, is seen. Under excitation with 325 nm one observes mainly the sharp luminescence lines related to , , and transitions in Tb3+ ions. One observes a strong pressure induced red-shift of the Ce3+ emission approximately equal to −20 cm−1 kbar−1 and much smaller shifts (approximately −1 cm−1 kbar−1) of the energies of the sharp lines related to Tb3+ luminescence. It has been found that the efficiency of energy transfer depends on Tb content and excitation energy; specifically, it is less effective when Tb3+ is excited to the lowest state of the excited 5d14f7 electronic configuration. This effect has been tentatively attributed to the nonradiative de-excitation of the Tb3+ ion to the metastable 5D4 state. A configurational model has been developed, which explains peculiarities of relaxation in the excited states of Tb3+ and energy transfer.