(INVITED) Review of luminescent properties of Ce3+-doped garnet phosphors: New insight into the effect of crystal and electronic structure

The absorption and luminescence properties (centroid shift and crystal field splitting of 5d orbitals) of Ce3+-doped garnets are summarized from the viewpoints of chemical composition (electron negativity and optical basicity) and the local crystal structure of the Ce3+ ion (bond length and distortion). Clear trends exist between (1) the centroid shift of 5d energy (εc) and the optical basicity of the host garnets and between (2) the crystal field splitting of the lowest 5d1-5d2 levels (Δ12) and a new distortion parameter obtained from the crystal structure data. The data of quantum yield and quenching temperatures of Ce3+-doped garnets are also considered, indicating the thermal ionization process as the main mechanisms for the quenching process. Based on our recent experimental results, to prove the thermal ionization process, the principle and the most important features of the photocurrent excitation (PCE) and thermoluminescence excitation (TLE) spectra measurements are summarized. Finally, a general trend for the quenching temperature of Ce3+ luminescence in the garnets is discussed in terms of the energy gap between the lowest 5d1 level and the conduction band bottom obtained from the vacuum referred binding energy (VRBE) diagram.