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We present the band gap engineering and morphological tuning of BaAl2O4:0.1% Sm3+, x% Tb3+ nanophosphors synthesized by citrate sol–gel method. Herein, the samarium (Sm3+) concentration is kept constant at 0.1%, while the concentration of terbium (Tb3+) is tuned from 0.5 to 2.5% with steps of 0.5%. X-ray diffraction confirms the hexagonal crystal structure of the BaAl2O4:0.1% Sm3+, x% Tb3+ nanophosphors. The reduction in crystallite size from 38 to 31 nm is noticed after doping and co-doping. Scanning electron microscope micrographs display evolution in morphology from multimodal grain-like structures to agglomerated pointy nanorods. Energy dispersive X-ray spectroscopy confirms all the main elements, although Sm is not detected due to the low content incorporated into the lattice. Transmission electron microscope results reveal that the particle size and shape can be controlled by varying concentrations of Tb3+. Diffuse reflectance spectra with the aid of the Kubelka–Munk function, reveal the energy band gap in the range of 2.6–5.3 eV. Under the excitation wavelength of 235 nm, photoluminescence studies reveal eight emission peaks located between 380 and 641 nm characteristic of Tb3+ ions. Upon the excitation wavelength of 402 nm, the emission spectra show four peaks positioned at 564, 601, 648 and 708 nm attributed to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2,4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 transitions of Sm3+ ions, respectively. From the colour coordinate results, this nanophosphor can successfully play a significant role in green, yellow and red LED applications. [ABSTRACT FROM AUTHOR]

In this work, trivalent Yttrium doped calcium aluminate (CaAl 2 O 4 :x% Y 3+ ) were synthesized for the first time. Through Photoluminescence (PL) spectroscopy and Commission Internationale de l'Eclairage (CIE), CaAl 2 O 4 :0.1 % Y 3+ has demonstrated to be a potential high emitting phosphor material amongst other high concentration Y 3+ doped samples, emitting a vibrant blue - pink hue where others are emitting a transiting hue from blue to green within a white vertex region. FTIR and UV-Vis have confirmed the prepared material and the presence of Y dopant. The SEM showed insignificant morphological change and the presence of pores, which were quantified using BJH and DFT methods to be micro - and meso-pores. Moreover, CaAl 2 O 4 is also being reported as a positive electrode in supercapacitors for the first time. The analysis shows that it has superior performance within 1 M KOH electrolyte, with a specific capacity of 47.71 mA h g -1  at 1 A g -1 and a maximum power of 39.68 kW kg -1 . Trasatti's method showed a surface (138 Fg -1 ) and diffusion (695 Fg -1 ) contribution ratio of 17:83 (%) of the total stored energy. It has a capacity retention and columbic efficiency of 100 % at the end of 10 000 cycles, which was achieved via utilization of all micropores reaction sites. The EIS showed a small solution resistance of 0.75 Ω, indicating high ionic conductivity and a phase angle of - 50 ° . Thus, these results show that CaAl 2 O 4 is a potential candidate for photoluminescence and energy storage application., Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:M.R. Mhlongo reports financial support was provided by 10.13039/501100001321National Research Foundation. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 Published by Elsevier Ltd.)

BaAl 2 O 4 /CaAl 2 O 4 /Ca 4 Al 6 O 13 /Ca 3 Al 2 O 6 :x% Sm 3+ (0 ≤ x ≤ 1.9) (hereafter called BCCC:x% Sm 3+ ) nanophosphors were successfully prepared by citrate sol-gel method. The structure, morphology and photoluminescence properties of the prepared nanophosphors were investigated. X-ray diffraction (XRD) indicated that the nanophosphors composed of the mixed phases of the hexagonal (CaAl 2 O 4 , BaAl 2 O 4 ) and cubic (Ca 4 Al 6 O 13 , Ca 3 Al 2 O 6 ) crystal structures. Scanning electron microscopy (SEM) revealed that doping influences the morphology of the prepared nanophosphor. High resolution transmission electron microscopy (HR-TEM) confirmed that the prepared phosphor particles are in the nanoscale range. Photoluminescence (PL) results showed emission peaks originating from the intrinsic defects within the BaAl 2 O 4 , CaAl 2 O 4 and Sm 3+ transitions. The optimum luminescence intensity was found at 0.7% Sm 3+ . Commission Internationale de l'éclairage (CIE) shows that the Sm 3+ doped samples emitted the orange colour., Competing Interests: The authors declare no conflict of interest., (© 2022 The Author(s).)