White light emitting LaGdSiO₅:Dy³⁺ nanophosphors for solid state lighting applications

Powdered dysprosium (Dy³⁺) doped Lanthanum gadolinium oxyorthosilicate (LaGdSiO₅) mixed phosphors were synthesized using urea-assisted solution combustion method. The X-ray diffractometer analysis showed that the samples crystalized in the pure monoclinic mixed phase of LaGdSiO₅. The crystallite size and the lattice strain calculated from the X-ray diffraction peaks using Williamson-Hall equation varied from 12 nm to 16 nm and 1.6×10^-2 to 2.43×10^-2 respectively. The photoluminescence (PL) emission spectra recorded using 425, 454 and 475 nm excitation wavelengths exhibit characteristic similar to the YAG:Ce phosphor pumped InGaN LED system, by absorbing portion of the excitation energy and re-emitting it. The emission spectra were characterized by radiative recombination at 425, 454, 475, 485 and 575 nm depending on the excitation wavelength. These emission line are ascribed to the f→f transitions of Dy³⁺. The peak intensity and hence the color of the emitted visible light were dependent on the concentration of Dy³⁺. The International Commission on Illumination (CIE) color coordinates of (0.336, 0.313) and (0.359, 0.361) were obtained for Dy³⁺ molar concentration of 0.05 and 3.0 mol% when the emission was monitored using 454 nm and 475 nm respectively. The band gap measured from the reflectance curve using Tauc plot initially decreased with increasing Dy³⁺ concentration, but at higher concentration, it started to increase. These materials were evaluated for solid state lighting application.