Interionic energy transfer in Y₃Al₅O₁₂: Ce³⁺, Pr³⁺ phosphor

We present an investigation of dynamical processes of nonradiative energy transfer (ET) between Ce³⁺ and Pr³⁺, and between Pr ³⁺ ions in Y₃ Al₅O₁₂: Ce ³⁺, Pr³⁺ phosphor. Photoluminescence spectroscopy and fluorescence decay patterns are studied as a function of Pr³⁺ and Ce³⁺ concentrations. The analysis based on Inokuti-Hirayama model indicates that the ET from the lowest 5d state of Ce³⁺ to the D1 2 state of Pr³⁺, and the quenching of the D1 2 state through a cross relaxation involving Pr³⁺ ions in the ground state are both governed by electric dipole-dipole interaction. An increase in the Ce³⁺- Pr³⁺ ET rate followed by the enhanced red emission line of Pr ³⁺ relative to the yellow emission band of Ce³⁺ on only increasing Ce³⁺ concentration is observed. This behavior is attributed to the increase in the spectral overlap integrals between Ce ³⁺ emission and Pr³⁺ excitation due to the fact that the yellow band shifts to the red spectral side with increasing Ce³⁺ concentration while the red line dose not move. For Ce³⁺ concentration of 0.01 in YAG: Ce³⁺, Pr³⁺, the rate constant and critical distance are evaluated to be 4.5× 10-36 cm ⁶ s^-1, 0.81 nm for Ce³⁺-Pr³⁺ ET and 2.4× 10-38 cm⁶ s^-1, 1.30 nm for Pr ³⁺-Pr³⁺ ET. Spectroscopic study also demonstrates a pronounced ET from the lowest 4f5d of Pr³⁺ to the 5d of Ce ³⁺. A proportional dependence of the initial transfer rate on acceptor concentration is observed in each of these ET pathways. The proportional coefficient as the averaged ET parameters for initial decay are determined, meaning the ET efficiency for the same concentration of acceptors follows the order of Pr³⁺-Pr³⁺ > Pr³⁺- Ce³⁺ > Ce³⁺-Pr³⁺.