Synthesis and Photoluminescence Properties of Deep-Red-Emitting CaYAlO4:Cr3+ Phosphors

Deep-red-emitting CaYAlO4:Cr3+ phosphors were synthesized by the sol–gel method followed by heat treatment. The effects of sintering temperature on the phase structure, morphology, and luminescence properties of the phosphors were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy, Raman scattering spectroscopy, energy-dispersive X-ray spectroscopy, steady-state photoluminescence (PL), and time-resolved luminescence spectroscopy. The XRD patterns showed that tetragonal CaYAlO4 crystals with space group I4/mmm were obtained after sintering at > 900°C. These experimental data were consistent with Raman spectra and FESEM images. A deep-red emission band at approximately 742 nm from CaYAlO4:Cr3+ phosphors was observed. This band was attributed to the transitions between the 2Eg and 4A2g energy levels of Cr3+ ions located at the CaYAlO4 host's lattice sites with D3d symmetry. Two absorption bands were recorded at near-ultraviolet and yellow regions. The highest PL intensity was obtained for phosphors with a Cr3+ doping concentration of about 0.7 mol.%. The PL decay dynamics of the materials with different doping Cr3+ concentrations were further investigated. All decay dynamics were featured with multiple decay components. The longest decay component with a lifetime of about 5.5 ms was obtained for the sample with the highest PL intensity. These optical behaviors were correlated with the critical distances of Cr3+ ions for energy transfers. Finally, the temperature dependence of deep-red PL emission was also investigated and discussed.