Spectrum designation and effect of Al substitution on the luminescence of Cr doped ZnGa2O4 nano-sized phosphors

Low-temperature photoluminescent spectra of ZnGa₂O₄:Cr³⁺ nano-sized phosphors calcined at different temperatures were reported. The fine structure of the emission spectra has been designated to Cr³⁺ ions in different sites including ideal octahedral, Zn-interstitial, sites and Ga₂O₃ impurity. The vibronic sidebands for both Stokes’ and anti-Stokes’ sides are related to the host lattice vibrations, which were confirmed by IR and Raman spectra. Al³⁺ is substituted in Ga³⁺ sites to form (0≤y≤0.5). The blue shift and luminescent intensity variations of the charge transfer band and 3d-3d transitions in the spectra caused by Al substitution were related to larger band gap and stronger crystal field, respectively. The calculated crystal-field parameters indicated that Al incorporation enhanced the crystal field strength and induced more trigonal distortion due to different radii of Al³⁺ and Ga³⁺.