Photoluminescence properties of Mn⁴⁺-activated oxide phosphors for use in white-LED applications: A review

The photoluminescence (PL) properties of Mn⁴⁺-activated oxide phosphors are reviewed. The phosphor materials considered here are almost all the oxide phosphors ever-reported, including germinates, silicates, aluminates, perovskites, double perovskites, and so on. These oxide phosphors can be classified into three groups, namely, types A, B, and C, from their different PL spectral features. Phosphors of type A clearly reveal a zero-phonon line (ZPL) emission peak due to the ²E_g → ⁴A_2g transitions in the Mn⁴⁺ ion together with the Stokes and anti-Stokes sideband peaks; however, the type-C phosphors promise no clear identification of the ZPL emission peaks even in the PL spectra measured at cryogenic temperatures. The ZPL emission peaks in the type-B phosphors can be tentatively determined from an analysis of the PL spectra using a characteristic Poisson function. The ZPL absorption transition energies in the PL excitation spectra of the type-A, -B, and -C phosphors are determined by performing Franck–Condon analysis within the configurational-coordinate (CC) model. These transition energies and ZPL emission energies are used to obtain the crystal-field (Dq) and Racah parameters (B and C) of the Mn⁴⁺ ions in those Mn⁴⁺-activated oxide phosphors. Temperature dependence of the PL intensity is also analyzed on the basis of the CC model and found to be in excellent agreement with the experimental data when both the optical and acoustic phonon contributions are taken into consideration in the conventional thermal quenching model.