Effects of Cr3+ and Al3+ co-doping on the spontaneous and stimulated luminescence of MgTa2O6

Near-infrared (NIR) luminescent materials play a vital role in photonic, optoelectronic, and biological applications. In this work, MgTa₂O₆: 1 mol% Cr³⁺ samples doped with different Al³⁺ concentrations were synthesized by a solid-state chemical reaction at 800 °C for 8 h after ball-milling the mixed precursors. X-ray diffraction (XRD) was used to confirm that the sample crystallized into a single phase, without impurities. Scanning electron microscopy (SEM), was used to confirm the morphology, which consists of irregular particles, and energy dispersive spectroscopy (EDS) confirmed the presence of Mg, Ta, O, Cr, as well as Al. Incorporating Cr³⁺ and Al³⁺ into the host reduced the optical energy band gap of the material from 4.34 to 4.31 eV. The results showed that adding Al³⁺ can improve the photon absorption of the Al³⁺ co-doped MgTa₂O₆: 1mo% Cr³⁺, enhancing its emission intensity. The photoluminescence (PL) spectra displayed a broad emission between 700 and 900 nm, with a barycentre at 850 nm, when the samples were excited at 280 nm. The emission originates from the spin-allowed transition, ⁴T₂ - ⁴A₂, of Cr³⁺ ions.Additionally, the decay curve was recorded, and the extracted time parameter corresponding to the luminescence was 29.79 ± 0.11 μs. The presence of electron trapping centres was confirmed using thermoluminescence (TL) spectroscopy. The depths of the electron trapping centres were approximated to be 0.69 ± 0.05, 0.77 ± 0.04, and 1.21 ± 0.04 eV, respectively. Finally, density functional theory (DFT) was applied to understand the electronic and optical properties with pronounced effects attributed to the presence of the Cr³⁺ ions. The study suggests that Al³⁺ doping MgTa₂O₆: 1 mol% Cr³⁺ has potential applications in solid-state lighting, safety illumination, and possible future development of PersL applications, etc.