Effect of Li⁺ monovalent ion on the structural and optical properties of Dy³⁺ doped ZnGa₂O₄ phosphor

This study reports enhancing the emission intensity of Dy³⁺ doped zinc gallate phosphor via Li⁺ monovalent co-doping. 2–12 mol% Li⁺ co-doped samples and a 0.05 mol% Dy³⁺ doped sample were synthesized using a solid-state synthesis technique. X-ray powder diffraction was used to analyze the phase of the synthesized phosphors. By recording the reflectance, the absorption properties were quantified using Ultraviolet-Visible spectroscopy, which displayed absorption peaks corresponding to the Dy³⁺ activator ions. The Kubelka-Munk function was used to estimate the bandgap and its variation concerning co-dopant concentrations. Energy dispersive electron spectroscopy and field emission scanning electron microscopy have been used to analyze the individual samples’ elemental composition and surface morphology. Surface mapping was also conducted using time-of-flight secondary ion mass spectrometry. X-ray photoelectron spectroscopy (XPS) was carried out for the 2 and 10 mol% Li⁺ co-doped samples to understand the structural properties. XPS confirmed the presence of anti-site defects in the synthesized samples. Phosphorescence spectra were recorded to analyze the effect of the Li⁺ co-doping on the excitation and emission, which showed a substantial increase in intensity. Apart from Dy³⁺ characteristic emission, all samples exhibited defect emission using a 299 nm excitation wavelength. The luminescence decay time for both types of emission spectra was recorded and found to be in microseconds. The thermoluminescence technique was used to quantify the trap states created between the valance and conduction bands. The analyzed samples were found to have more than one trap with varying trap densities and activation energies. The color chromaticity coordinates were determined for each sample regarding defect emission and the characteristic emission of the Dy³⁺ activator ions to assess the color of the emission generated. The information obtained shows promising possibilities that this phosphor material may be a good fit for light-emitting diodes and display technologies based on the emission wavelengths produced.