Origin of Spectral Blue Shift of Lu³⁺-Codoped YAG:Ce³⁺ Phosphor: First-Principles Study

Lu³⁺, with the smallest ionic radii in lanthanide ions, is an important and beneficial cation for tuning spectrum shifting toward a longer wavelength by ion substitution in many phosphors for solid-state lighting. However, in the Lu³⁺-substituted garnet system, the phosphor always has smaller lattice parameters and exhibits a shorter emission wavelength than other garnet phosphors. The mechanism of such a spectral blue shift induced by the Lu³⁺-codoped garnet phosphor is still unclear. In this study, the local and electronic structures of Lu³⁺-codoped and Lu³⁺-undoped YAG:Ce³⁺ phosphor have been studied by first-principles calculation to reveal the origin of the spectral blue shift. Our results provide a full explanation of the experimental data and the methodology, which is useful to understand and design garnet phosphors with tunable emission characteristics.