Band gap engineering and morphological tuning of BaAl2O4:Sm3+, Tb3+ nanophosphors induced by various concentrations of terbium ions: green, yellow and red dual emission nanophosphor.

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]