Visible Upconversion Emission of Pr³⁺ Doped Gadolinium Gallium Garnet Nanocrystals

The luminescence properties of a Pr³⁺ -doped gadolinium gallium garnet (GGG, Gd₃Ga₅O₁₂) nanocrystalline host were investigated. Dominant blue/green emission was observed emanating from the ³P₀ → ³H₄ transition after excitation using a wavelength of 457.9 nm. Continuous wave excitation into the ¹D₂ level of the Pr³⁺ ion at 606.9 nm transition produced blue upconversion luminescence spectra, ascribed to emission from the ³ P₁ → ³H₄ and³ P₀ → ³H₄ transitions. The increase in the decay times of the observed transitions following excitation with 606.9 nm is indicative of the dominance of an energy transfer upconversion (ETU) mechanism relative to excited state absorption (ESA). Furthermore, blue, green and red upconversion emission was observed from the³P₀ , ³P₁ and ¹D₂ states following excitation into the ¹G₄ energy level with 980 nm. No change in the decay times of the emitting states was observed following excitation with a wavelength of 980 or 457.9 nm; hence, upconversion was determined to primarily occur through ESA. The luminescence properties of the nanocrystals are compared to a single crystal of GGG:Pr³⁺; (bulk) with an identical Pr³⁺ concentration (1%).