Effect of annealing period on the structure, morphology, and optical properties of CaAl2O4:0.1% Sm3+ prepared by citrate sol-gel method

• Published in: Journal of molecular structure Vol. 1260; p. 132751
• Main Authors: Mabelane, T.S., Koao, L.F., Motloung, S.V., Motaung, T.E., Kroon, R.E., Mhlongo, M.R.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-07-2022
• Subjects: Annealing period (AP); CaAl2O4; Nanopowders; Photoluminescence (PL); Sm3; Sol-gel; Sm3; Annealing period (AP); Nanopowders; CaAl2O4; Photoluminescence (PL); Sol-gel
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2022.132751

•The prepared nanophosphor resembles the monoclinic CaAl2O4.•Annealing period influences the crystallite sizes of the prepared nanophosphor.•The morphology was greatly influenced by annealing period.•Photoluminescence (PL) results showed 6.9 h as the optimum annealing period of the prepared nanophosphor.•The energy band gap and the greenish colour from samarium can be tuned by varying the annealing period.
We report on the variation of annealing period (AP) in the range 1–8 h on samarium doped calcium aluminate (CaAl2O4:0.1%Sm3+) powders prepared by sol-gel method. The effect of AP was investigated on the structure, morphology and optical properties of the powders. The X-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS) findings showed that Sm3+ ions were successfully doped into CaAl2O4. XRD confirmed that AP does not have any effect on the phase of the prepared nanopowders, hence all the samples have a monoclinic structure. Scanning electron microscope (SEM) showed that as AP increases the particles became more agglomerated and smoother. The energy band gap (Eg) was affected by the increase in AP. Ultraviolet-visible (UV–vis) diffuse reflection spectroscopy demonstrated that Eg can be tuned between 5.56 and 5.71 eV. The photoluminescence (PL) emission spectrum upon excitation of 403 nm displayed ten emission peaks located at around (559, 564 and 576), (601 and 608), (643, 648, 653 and 662) and 708 nm. These emission peaks can be ascribed to the 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2→6H9/2 and 4G5/2→6H11/2 transitions of Sm3+ ion, respectively. It further showed that the optimum luminescence intensity occurred for AP = 7 h. The Commission Internationale de l'Eclairage (CIE) analysis revealed that AP has tuned the emission colour from greenish to orange-red. The results indicate that the prepared nanopowders can potentially be used in the orange/red emitting phosphors.