Tailoring Photophysical Processes of Er³⁺‐Doped Gd₃Ga₅O₁₂ Garnets for Enhanced Photoluminescence via Al³⁺ Ion Preference Substitution

ABSTRACT Rare‐earth ion‐doped garnets with excellent luminescent properties show great potential for temperature sensing, displays, and nondestructive detection. However, their limited luminescent modes and low photoluminescence quantum yields (PLQY) restrict further applications. In this study, we synthesized Al³⁺, Er³⁺‐co‐doped Gd₃Ga₅O₁₂ garnets with multimode luminescence via a high‐temperature solid‐state method. Notably, the preferential substitution of Al³⁺ ion at octahedral‐coordinated Ga^I sites significantly enhanced the charge density and electron transition probability, achieving a PLQY enhancement of the down‐shifting luminescence from 35.1% to 68.5%. Al³⁺ ion also influences electron relaxation during up‐conversion luminescence, resulting in a color shift from red to yellow to green. Additionally, Al³⁺ incorporation increased the photoelectric conversion efficiency of light‐emitting diodes from 2.9% to 6.3% and improved temperature sensing sensitivity from 2.7% to 5.1% K⁻¹. This work provides new insights into the photophysical mechanisms and underscores the key role of Al³⁺ ion in optimizing the optical properties of garnet‐based materials.