EPR and photoluminescence properties of Mn2+-activated zinc gallate phosphor prepared by urea combustion route and post heat treatment

Mn2+ activated ZnGa2O4 powder phosphors have been prepared by urea combustion route. Powder X-ray diffraction and scanning electron microscopy (SEM) techniques have been used to characterize the as-prepared and post-treated (900 °C, 3 h) phosphors. The morphology shows small particles, voids and pores, with non-uniform shapes and sizes. The EPR spectrum exhibits an intense resonance signal at g≈1.985 with a sextet hyperfine structure (hfs) besides a weak broad signal at g≈4.05 and a hump near g≈2.27. The g≈1.985 resonance is due to Mn2+ ions in an environment close to tetrahedral symmetry. The resonances at g≈4.05 and 2.27 are attributed to the rhombic surroundings of the Mn2+ ions. The spin concentration (N) and the paramagnetic susceptibility (χ) are evaluated and discussed. It is observed that the intensity of the resonance signal at g≈1.985 increases with decrease in temperature obeying the Boltzmann law. Upon post treatment the intensity of the green emission (λem=528 nm,4T1→6A1 transition of Mn2+ ions) has been increased to 3.35 times and a red shift has been observed.