Size-Tunable Phosphorescence in Colloidal Metastable γ-Ga₂O₃ Nanocrystals

Abstract

We report a colloidal synthesis of gallium oxide (Ga(2)O(3)) nanocrystals having metastable cubic crystal structure (gamma phase) and uniform size distribution. Using the synthesized nanocrystal size series we demonstrate for the first time a size-tunable photoluminescence in Ga(2)O(3) from ultraviolet to blue, with the emission shifting to lower energies with increasing nanocrystal size. The observed photoluminescence is dominated by defect-based donor-acceptor pair recombination and has a lifetime of several milliseconds. Importantly, the decay of this phosphorescence is also size dependent. The phosphorescence energy and the decay rate increase with decreasing nanocrystal size, owing to a reduced donor-acceptor separation. These results allow for a rational and predictable tuning of the optical properties of this technologically important material and demonstrate the possibility of manipulating the localized defect interactions via nanocrystal size. Furthermore, the same defect states, particularly donors, are also implicated in electrical conductivity rendering monodispersed Ga(2)O(3) nanocrystals a promising material for multifunctional optoelectronic structures and devices.

Light-emitting Ga-oxide nanocrystals in glass: a new paradigm for low-cost and robust UV-to-visible solar-blind converters and UV emitters

“…The same evaluation provides us with an estimation of the mean value of QC shi DE ex of approximately 0.06 eV, hard to be detected as a convoluted shi of the absorption edge, as correctly argued in a previous work. 20 This value permits however estimation of an expected E G in bulk of about 4.4 eV, important to gives us a rst insight into a crucial feature of g-Ga 2 O 3 NCs grown on glass. In fact, the relatively small E G value of the related bulk phase suggests a quite relevant content of oxygen vacancies V $ O per NC.…”

“…However, such an effect was rarely registered, if any, in the optical absorption spectrum of Ga 2 O 3 . 5,20 Actually, in nanosystems, the optical absorption edge arises from additive contributions of all NCs, each characterized by specic size-dependent QC according to 52…”

Surface-specific visible light luminescence from composite metal oxide nanocrystals

“…1) [3,4]. In some wide band gap semiconductors, significant luminescence can even be observed in undoped materials due to the presence of intrinsic defects [20][21][22][23]. While rare-earthdoped materials are currently employed commercially, there are a number of issues associated with supply, toxicity, and non-radiative surface recombination at surfaces which are problematic [2,24,25].…”

Diffusion-driven and size-dependent phase changes of gallium oxide nanocrystals in a glassy host

“…22,23 It can be prepared as powder or nanopowder, either from a high temperature calcination process of gallia gel, [22][23][24] or through solution-based syntheses from organic molecular precursors. 25,26 g-Ga 2 O 3 irreversibly transforms into b-Ga 2 O 3 via a two step phase change involving an intermediate reversible change into a g 0 -Ga 2 O 3 phase. 27 d-Ga 2 O 3 was first observed as a result of heating of evaporated gallium nitrate solution at 470-520 K. 28 It was identified as a distinct polymorph with C-type rare earth sesquioxides, 28 but new recent data suggest that d-Ga 2 O 3 is probably a nanocrystalline form of e-Ga 2 O 3 and not a distinct polymorph.…”