Structure, morphology and optical-luminescence investigations of spinel ZnGa₂O₄ ceramics co-doped with Mn²⁺ and Eu³⁺ ions

Abstract

The polycrystalline zinc gallate ZnGa₂O₄: Mn²⁺ and ZnGa₂O₄: Mn²⁺, Eu³⁺ samples have been synthesized via high-temperature solid-state reaction ceramic technique. The obtained ceramics have been characterized employing the methods of X-ray diffraction analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, positron annihilation lifetime spectroscopy and optical-luminescent spectroscopy. The XRD analysis testified in favor of successful formation of spinel structure in the prepared samples with small amount of additional phase observed in the ZnGa₂O₄: Mn²⁺, Eu³⁺ ceramics. The grains of irregular shape with a homogeneous distribution of Eu³⁺ ions in a volume were identified with TEM technique. The band gap of ZnGa₂O₄: Mn²⁺ spinel was estimated from optical absorption spectra in UV–Vis range. The characteristic bands related to electronic transitions of Mn²⁺ and Eu³⁺ ions were found in optical absorption and excitation spectra. The photoluminescence emission spectra exhibited matrix luminescence along with emission band of Mn²⁺ ions and narrow lines of Eu³⁺ ions in blue, green and red spectral region, respectively. The intensity ratio of Eu³⁺ emission lines confirms the high asymmetry around Eu³⁺ ions. These findings correlate well with results of positron annihilation lifetime spectroscopy showing intense reduction of positron trapping rate deeply in ceramics grains due to Eu³⁺ ions penetration.