Correlation between native defects and dopants in colloidal lanthanide-doped Ga2O3 nanocrystals: a path to enhance functionality and control optical properties

Abstract

We report the synthesis and study of the photoluminescence properties of colloidal lanthanide(III)-doped Ga₂O₃ nanocrystals. The Ga₂O₃ nanocrystal host lattice acts as a sensitizer of the Eu³⁺ dopant red emission arising from intra-4f orbital transitions, and concurrently exhibits a strong blue photoluminescence originating from defect-based donor–acceptor pair (DAP) recombination. The Eu³⁺ sensitization, enabled by the energy transfer from the nanocrystal host lattice to the dopant centers, allows for the generation of dual blue-red emission. Increasing doping concentration leads to a decrease in the donor activation energy allowing for simultaneous control of the optical and electrical properties of these multifunctional nanocrystals. Analyses of the steady-state and time-resolved photoluminescence spectra suggest that Eu³⁺ ions occupy at least two different sites, which were tentatively designated as the six-coordinate internal and surface-related dopants. Uniquely, both DAP and Eu³⁺ emissions have long lifetimes (in milliseconds), although Eu³⁺ luminescence has a slower decay rate. These phenomena enable a temporal modulation of the dual emission and photoluminescence chromaticity on the millisecond timescale. The generality of these findings was demonstrated by preparing Tb³⁺-doped Ga₂O₃ nanocrystals, as a blue-green dual emitter. Owing to their optical transparency, electrical properties, emission color versatility, robustness, and fabricability, colloidal lanthanide(III)-doped Ga₂O₃ nanocrystals are a promising class of multifunctional materials and complex phosphors.