Nucleation-controlled vacancy formation in light-emitting wide-band-gap oxide nanocrystals in glass

Abstract

Light emission of nanocrystals (NCs) can depend not only on NC size but also -and even more importantly in wide-band-gap NCs -on the occurrence of optically active sites, such as donor-acceptor pairs (DAPs).Here, we demonstrate that controlling the thermo-chemical conditions of NC nucleation when NCs are forming in a solid host -an approach often used for driving NC size dispersion -can be an innovative strategy for tailoring DAP population. Our data show that light emission from DAP recombination and decay in defect sites can be controlled in g-Ga 2 O 3 NCs in alkali-germanosilicate glass -a prototypal oxide-in-oxide nanostructured system -by oxygen and gallium vacancy formation during nucleation.Time-resolved UV-excited photoluminescence, combined with differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy, reveal how nucleation pretreatment determines, besides NC size and concentration, also the DAP number via promotion of acceptor formation or their passivation during interaction with the host. The results envisage the possibility of nucleation-based design of light-emitting NCs in a wide range of oxide systems.

Donor–Acceptor Control in Grown‐in‐Glass Gallium Oxide Nanocrystals by Crystallization‐driven Heterovalent Doping

“…In summary, the analysis of DSC and XRD data shows that Ni and Ti doping can influence the glass nanocrystallization, with effects on size and concentration of γ‐Ga 2 O 3 NCs. Therefore, as NC size affects the balance between V O and V Ga sites inside each NC, we can expect a NC size‐related effect of doping on the donor–acceptor light‐emission properties of NCs. Furthermore, Ti 4+ and Ni 2+ ions substituting Ga 3+ can also play an even larger and more direct role in DAP and defect‐related optical emissions of the nanophase, provided that they enter into the NCs so as to modify the donor and acceptor populations by heterovalent substitution.…”

“…Starting from those results, some recent studies have demonstrated that DAP concentration per NC can be controlled, to some extent, by tailoring the NC size and, consequently, the concentration of V O per NC at fixed oxygen deficiency in the nanophase. This result has been obtained either in nanopowders of selected size, or in grown‐in‐glass NCs by thermal tuning of the nucleation process . Nevertheless, V O and V Ga are expected to be also influenced by doping with ions, substituting Ga 3+ with different oxidation states, as demonstrated in quantum dot (QD) colloids, so giving the prospect of a size‐independent method—driven by charge neutrality—to control the broadband visible‐light emission of Ga oxide at the nanoscale.…”

“…ders of selected size, or in grown-in-glass NCs by thermal tuning of the nucleationp rocess. [14,40,41] Nevertheless, V O and V Ga are expected to be also influenced by doping with ions, substituting Ga 3 + with different oxidations tates, as demonstrated in quantum dot (QD) colloids, [42,43] so giving the prospect of as ize-independent method-driven by chargen eutrality-to control the broadband visible-light emissiono fG a oxide at the nanoscale. However,d oping processes of nanophases,e specially in grown-in-glass systems, may causen onnegligible side effects on the nanophase size and concentration.…”

Pre-crystallization heat treatment and infrared luminescence enhancement in Ni2+-doped transparent glass-ceramics

“…This method was used as it can more accurately predict the temperature dependence of the nucleation rate rather than the peak height method in the case of considerable overlapping of the nucleation and growth processes [28]. The heat treatments were performed by placing the samples into the muffle furnace at room temperature, heating them at a rate of 10 °C/min up to 595 ºC (accuracy ±2 ºC) and holding for 2.5, 3.5, 4.5, 6.5 or 8.5 h. The treatment temperature was chosen according to previous data on similar glass indicating the occurrence of nucleation process in that range of temperatures [26].…”

“…In contrast, low-alkali gallium germanosilicates can be obtained at temperatures lower than 1500 ºC and after doping with Ni 2+ also demonstrate broadband NIR emission with comparable quantum yield [23][24][25]. Two-step heat treatment of Ni-free low-alkali gallium germanosilicates was shown to have notable impact on size and number of nanocrystals (NCs) of spinel-like gallium oxide precipitated in the glass matrix [26]. In regard to Ni 2+ -doped germanosilicates, only one-step heat treatment has been used up to now, and a strong correlation has been revealed between the number of Ni 2+ ions per NC and the integrated intensity of the related broadband NIR emission [24].…”