Concentration quenching behavior of Stokes and upconversion luminescence for Pr3+-doped Y3Al5O12

Abstract

Pr³⁺ ions exhibit Stokes and upconversion luminescence attributed to the 5d–4f interconfigurational and 4f–4f intraconfigurational transitions, whose intensity is sensitive to the Pr³⁺ concentration because of the interaction between neighboring Pr³⁺ ions. In this study, the Y₃Al₅O₁₂ (YAG) ceramics doped with high Pr³⁺ concentrations (1–20%) were synthesized using the polymerized complex method, and their Stokes and upconversion luminescence properties were characterized. While the Stokes 5d–4f luminescence bands in the ultraviolet (UV) region were insensitive to the Pr³⁺ concentrations below 5%, the Stokes 4f–4f luminescence in the visible to near-infrared region was notably quenched because of the cross-relaxation of the ³P₀ and ¹D₂ states. The YAG:Pr³⁺ samples exhibited UV upconversion luminescence in the UV region of 300–400 nm under high-power 455 nm blue laser diode illumination. The upconversion photoluminescence excitation spectra revealed two possible processes for Pr³⁺: 5d–4f upconversion luminescence, a spin-allowed two-photon absorption process via the intermediate ³P_J′ (J′ = 0, 1, and 2) states, and a multiphonon-relaxation-assisted process via the intermediate ¹D₂ state. The characterization of the Pr³⁺ concentration dependence revealed that the UV upconversion intensity was significantly affected by the cross-relaxation rates of the intermediate ³P₀ and ¹D₂ states. In this study, it was demonstrated that compounds with low Pr³⁺ concentrations or long Pr³⁺–Pr³⁺ distances that lower the cross-relaxation rates are advantageous for the development of visible-to-UV upconverting materials activated with Pr³⁺.