Analysis of Er³⁺ concentration on the structural, and optical properties of CaAl₂O₄: 0.1% Y³⁺, x% Er³⁺ (0 < x ≤ 2.0) synthesized using citrate sol–gel Method

This study reports the effect of Er³⁺co-doping on the structural and optical properties of CaAl₂O₄: 0. % Y³⁺, x% Er³⁺ (0 < x ≤ 2.0) synthesized by citrate sol–gel method. The X-ray diffraction (XRD) peaks appear well-defined and sharp, indicating a high level of crystallinity. Furthermore, the patterns verified that each sample exclusively comprised the monoclinic CaAl₂O₄ structure, indicating the presence of a single phase in all samples. Scanning electron microscopy (SEM) results show that doping influenced the morphology of the prepared powder. The Fourier Transform Infrared (FTIR) results exhibited a sequence of absorption peaks within the range of 450 to 2000 cm⁻¹. Ultraviolet–visible (UV–Vis) spectroscopy showed that doping influences the optical bandgap (E_g) of the prepared phosphor materials, and the E_g can be tuned between 4.93 and 5.44 eV. The photoluminescence (PL) analysis revealed multiple emission peaks located at 417, 440, 467, 492, 522, 546, 557, 568, 660, 671, 684 and 697 nm. The emissions observed at 417, 440, 467, and 492 nm were assigned to the intrinsic properties of the host material. The peak observed at 522 nm can be attributed to the ²H_11/2 → ⁴I_15/2 transition, while the peaks at 546–557 nm are associated with the ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ ions. The emission peaks falling within the 660–697 nm range suggest direct transitions from the ⁴F_9/2 excited states to the ⁴I_15/2 ground state of Er³⁺ ions. The Commission Internationale de l’Eclairage (CIE) diagram shows that the emission colour can be tuned from greenish blue to yellowish green by varying the concentration of Er³⁺.