Correlative Study of Vibrational and Luminescence Properties of Zn₂GeO₄ Microrods

Abstract

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.

Efficient white-light emission from Zn2GeO4 nanomaterials

“…The apparently shift of the visible band could be associated to changes in the ratio among their components, affecting most to the 2.44 eV component. This effect has also been observed in undoped samples and it has been linked to oxygen vacancies [17] . Concerning the UV emission, a clear shift to higher energies is detected by recording polarized light parallel to the microwire axis.…”

“…Raman spectra from undoped samples showed that relative intensity between modes changed as a function of the particular polarization orientation between the laser and the microwire. In particular, total and partial quenching of E g (4) and E g (3) modes, respectively, both perpendicular to c-axis, were attributed to the orientation of the wire along c-axis [17] . Figure 3 mode, related to vibration modes in O-Ge-O, it could be possible that Mg ions sited at Zn lattice locations would do not affect this mode, and, hence its dependence on the polarization conditions is the same that in the undoped case.…”

The role of surface properties in the cathodoluminescence of Zn2GeO4/SnO2 nanowire heterostructures

“…Figure 1b shows Raman peaks representative of the rutile phase of SnO 2 corresponding to the E g (478 cm −1 ), A 1g (634 cm −1 ) and B 2g (778 cm −1 ) vibration modes [5]. On the other hand, figure 1c shows the characteristic Raman peaks of the rhombohedral structure of Zn 2 GeO 4 (745, 751, 777 and 802 cm −1 ) associated with Ge-O-Zn symmetric and asymmetric vibration modes and the O-Ge-O bending and stretching modes [6,7]. The 520 cm −1 peak corresponds to the silicon substrate.…”

Kinetic Study of the Thermal Quenching of the Ultraviolet Emission in Zn2GeO4 Microrods

“…ZnO:Ge (1:1) precursors produces a huge white mat of structures after the dynamic thermal annealing that fully cover the substrate, as it can be observed in the optical image and in the secondary electron (SE) image of Figure 1a. The thermal treatment of the T(21) pellet produces as well similar Zn 2 GeO 4 microrods; however, the density of microstructures over the pellet is lower than in T (11). Figure 1b,c shows SE images with the detail of some Zn 2 GeO 4 microrods, in which most of them appear to exhibit a hexagonal cross-section shape.…”

“…In contrast, the influence of growth conditions on the equilibrium defect concentration and samples architecture has been appeared to play a critical role in the luminescence properties of Zn 2 GeO 4 . [4,[9][10][11][12] Thermal annealing of precursor materials containing Zn and Ge has been revealed as an effective method to produce high-quality crystalline Zn 2 GeO 4 microrods and nanowires under the vapor-solid mechanism. [5,13] In particular, luminescence in the UV and in the visible range depending on the probe energy, above of below the energy bandgap, has been observed in Zn 2 GeO 4 microrods synthetized by a thermal treatment of a mixture of ZnO and Ge.…”