Correlation between structural and optical properties of Dy[formula omitted] doped BaGd[formula omitted]O[formula omitted] phosphors intended for solid-state lighting applications

Abstract

Highly crystalline and single phase BaGd2−xDyxO4 (0.00 ≤x≤ 0.16) phosphors, with an average crystallite size around 126 nm, have been synthesised using solid-state reaction technique. The structural and optical properties of these phosphors have been studied in detail to establish an unambiguous correlation between these properties. High-angle annular dark field (HAADF) images have confirmed that the constituent elements are homogeneously distributed in the particles, and their elemental composition has been established using X-ray photoelectron spectroscopy (XPS). The tuning of optical band gap with x has been achieved, which is a rare achievement in these phosphors. Also, the optimum concentration of Dy3+ ions has been found to be 0.8 mol%, which is the lowest among the Dy3+ doped BaGd2O4 phosphors reported so far. This concentration quenching effect has been discussed on the basis of a combination of decay curve analysis, calculation of average critical distance between the Dy3+ ions and integrated intensities of photoluminescence (PL) emission bands. The average crystallite size and optical band gap has also been found to decrease after x = 0.016, from which their correlation with concentration quenching effect has been investigated. The asymmetry ratio between the integrated intensities of yellow and blue PL emission bands has been observed to be greater than 2 throughout x, which confirmed the preferential lattice site for Dy3+ ions in these phosphors with present synthesis conditions. The variation of asymmetry ratio and Gd3+-dominated IR-active lattice vibrations with x, and Vegard’s law pertaining to the volume of a unit cell confirms that the local bonding environment in the lattice of these phosphors gets modified at x = 0.016. The photometric parameters for these phosphors reveal their suitability for fabrication of warm light orange LEDs on appropriate UV chips.