Synthesis, Crystal Structure and Photoluminescent Properties of Red-Emitting CaAl₄O₇:Cr³⁺ Nanocrystalline Phosphor

Calcium dialuminate, CaAl4O7, nanopowders with a grossite-type structure, doped with chromium ions, were synthesized via the combined sol-gel solution combustion method. The evolution of phase composition, crystal structure, and microstructural parameters of the nanocrystalline materials depending on the temperature of the thermal treatment was investigated via X-ray powder diffraction and applying the Rietveld refinement technique. The photoluminescent properties of CaAl4O7 nanophosphors activated with Cr3+ ions were studied over the temperature range of 4.5-325 K. The samples show deep red and near-infrared luminescence due to the E-2 ? (4)A(2) and T-4(2) ? (4)A(2) energy level transitions of Cr3+ ions under excitation in the two broad emission bands in the visible spectral region. The R lines emission reveals a strong temperature dependence. The feasibility of the material for non-contact luminescence sensing is investigated, and good sensitivity is obtained based on the (R2/R1) luminescence intensity ratio and the lifetime of the emission.