Distance-Dependent Energy Transfer between Ga₂O₃ Nanocrystal Defect States and Conjugated Organic Fluorophores in Hybrid White-Light-Emitting Nanophosphors

We report a quantitative analysis and development of hybrid white-light-emitting nanoconjugates, prepared by functionalizing colloidal γ-Ga₂O₃ nanocrystals with selected organic fluorophores. Using the Förster resonance energy transfer (FRET) formalism, we studied the coupling of native defect states in Ga₂O₃ nanocrystals, as energy donors, with different orange-red-emitting fluorophores bound to nanocrystal surfaces, as energy acceptors. Variations in the average nanocrystal size and dye surface coverage were used to characterize the efficiency of the energy transfer process and the corresponding donor–acceptor separations. The results show that for approximately three rhodamine B molecules per nanocrystal the energy transfer efficiency increases from 23% to 49% by decreasing the NC size from 5.3 to 3.6 nm. These FRET efficiencies correspond to the estimated donor–acceptor distances of 3.55 ± 0.02 and 2.99 ± 0.03 nm, respectively. Similar trends were observed for ATTO 590-conjugated Ga₂O₃ nanocrystals, although ATTO 590 proved to be a more effective energy acceptor owing to a larger molar extinction coefficient in the conjugated form. The size-dependent luminescence of Ga₂O₃ nanocrystals and the control of FRET parameters through the variations in the bound dye molecules allow for the generation of tunable blue-orange emission, ultimately resulting in white light with targeted chromaticity and high color rendition