Tuneable blue-green co-activated CaAl2O4: 0.1 mol% Tb3+, x mol% Sm3+ (0 ≤ x ≤ 2) nanophosphor prepared by citrate sol-gel method

This study reports the analysis of tuneable blue-green phosphor of calcium aluminate (CaAl2O4) co-doped with terbium (Tb3+) and varying concentration of samarium (Sm3+) (0 ≤ x ≤ 2). The powder samples were synthesized by using the citrate sol-gel method and annealed at 900 °C for 2 h (h) for all samples. The X-ray powder diffraction (XRD) results revealed a developing amorphous monoclinic structure of CaAl2O4. Co-doping with Tb3+ and Sm3+ slightly affected the structure of synthesized CaAl2O4. Scanning electron microscope (SEM) results showed that co-doping the host material of CaAl2O4 slightly affected the morphology of the synthesized nanopowders. The transition electron microscope (TEM) images showed that the particle sizes of the host material were affected by doping. Ultraviolet–visible (UV–Vis) reflection spectroscopy suggested that the band gap of co-doped CaAl2O4:0.1 mol% Tb3+, x% Sm3+ (0 ≤ x ≤ 2) ranges between 5.05 and 5.20 eV. The photoluminescence (PL) results showed several emission peaks located at 420, 440, 484, 548, 558, 562, 584, 603 and 654 nm. Emission peaks at 420, 440, 484 and 558 nm were attributed to the host material. The peaks at 548 and 558 nm are originating from 5D4→7F6 and 5D4→7F5 transitions of Tb3+ while the peaks at 562, 603 and 654 nm seems to be originating from the dopant of Sm3+ which may be assigned to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, and 4G5/2 → 6H9/2 transitions of Sm3+, respectively. CIE coordinates results suggested that the emission colour can be tuned from bluish to greenish as x% Sm3+ concentration is varied. •The prepared nanophosphor is a monoclinic developing amorphous structure of the CaAl2O4:0.1%Tb3+, x%Sm3+.•The crystallite size increases from 29 to 32 nm after doping and co-doping.•Photoluminescence (PL) showed emission peaks at 420, 440, 484, 548, 562, 603 and 654 nm assigned to the host material and transitions of Tb3+ and Sm3+.•Band gap may be tuned between 5.05 and 5.20 eV.•The emission colour was tuned from bluish to greenish.