Achieving efficient and stable ultraviolet emission is a challenging goal in optoelectronic devices. Herein, we investigate the UV luminescence of zinc germanate Zn 2 GeO 4 microwires by means of photoluminescence measurements as a function of temperature and excitation conditions. The emitted UV light is composed of two bands (a broad one and a narrow one) associated with the native defects structure. In addition, with the aid of density functional theory (DFT) calculations, the energy positions of the electronic levels related to native defects in Zn 2 GeO 4 have been calculated. In particular, our results support that zinc interstitials are the responsible for the narrow UV band, which is, in turn, split into two components with different temperature dependence 1 arXiv:2007.15336v1 [cond-mat.mtrl-sci] 30 Jul 2020 behaviour. The origin of the two components is explained on the basis of the particular location of Zn i in the lattice and agrees with DFT calculations. Furthermore, a kinetic luminescence model is proposed to ascertain the temperature evolution of this UV emission. These results pave the way to exploit defect engineering in achieving functional optoelectronic devices to operate in the UV region.

Herein, we report the formation of a particular core–shell structure, with a zinc germanate (Zn2GeO4) nanowire core and a discontinuous shell of SnO2 nanocrystals, obtained in a single-step process. We propose a growth model that combines the Plateau–Rayleigh mechanism to produce a pattern of amorphous germanium oxide (a-GeO2) particles along the Zn2GeO4 nanowire and the subsequent growth of well-faceted SnO2 crystals when the nanowire orientation meets good lattice matching conditions. In this latter case, the linear array of a-GeO2 particles acts as nucleation sites for the SnO2 crystallites, leading to a skewer-like morphology that retains the periodicity of the Plateau–Rayleigh process. Otherwise, nanowires with different orientations appear decorated with a pattern of a-GeO2 beads mimicking a necklace. Atomic resolution electron microscopy has been used to characterize the Zn2GeO4/SnO2 nanoheterostructures. In addition, optical confinement effects have been observed in the luminescence maps and spectra, which have potential for further exploitation in the design of optical microcavities.

The optical properties of zinc germanate microrods are investigated and correlated with vibrational modes of the crystalline structure. The samples are grown by a thermal evaporation method using ZnO and Ge as precursors. Polarized Raman spectroscopy and polarized micro‐photoluminescence techniques are applied in order to shed some light into the origin of the luminescence in Zn2GeO4. Oxygen defects are usually responsible for light emission in most of semiconducting oxides. Here, the authors report two luminescence bands at room temperature, a broad green one at about 2.4 eV and an ultraviolet one at 3.2 eV, which are of composed nature. In addition, the authors observe changes in the Raman and PL spectra recorded with polarizers oriented parallel or orthogonal to the microrod axis. The evolution of the luminescence bands in Zn2GeO4 and their correlation with the observed Raman modes (O‐Ge‐O and Ge‐O‐Zn vibration modes) are discussed in the framework of oxygen defects in the Zn2GeO4 structure.

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