Photoluminescence and EPR Study of the Local Environment of Gd3+ in SrAl4O7 UVB Phosphors

Abstract

Phosphor materials play a crucial role in the advancement of optical technologies. In this study, SrAl₄O₇:xGd³⁺ (x = 0.01–0.11 mol) phosphors are synthesized using the combustion method, and their structural, morphological, and optical properties are examined. X-ray diffraction analysis confirms that the phosphors crystallize in the monoclinic C2/c space group. Photoluminescence spectroscopy indicates well-defined intra-configurational 4f–4f transitions of Gd³⁺ ions, with prominent emission peaks at 308 nm and 314 nm, corresponding to the ⁶P_5/2 → ⁸S_7/2 and ⁶P_7/2 → ⁸S_7/2 transitions, respectively. The luminescence intensity is optimized at a Gd³⁺ concentration of 0.09 mol. The electron paramagnetic resonance spectra of SrAl₄O₇:Gd³⁺ phosphors exhibit a prominent resonance line at an effective g-factor of approximately 1.97, accompanied by weaker signals in the low-field region. Two distinct Gd³⁺ sites with differing local environments contribute to the observed spectrum. These environmental variations arise from charge-compensating Sr²⁺ vacancies or interstitial O²⁻ ions and their proximity to Gd³⁺ ions. The findings highlight the potential of Gd³⁺-doped SrAl₄O₇ for advanced UV photonic applications, particularly in dermatological phototherapy, where precise control over emission properties is crucial.