Investigations on photoluminescence and energy transfer studies of Sm3+ and Eu3+ ions doped Sr9Y2W4O24 red emitting phosphors with high color purity for w-LEDs

Abstract

Sm3+/Eu3+ co-doped Sr9Y2W4O24 phosphors were prepared using the solid-state reaction process. The structure and micro-morphological analysis of the as-prepared phosphors were explored via x-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Optical & spectroscopic characteristics were investigated by the mean of diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) techniques. The Sr9Y2W4O24 phosphor is tetragonal in structure and belongs to the I41/a space group. The excitation spectra recorded demonstrates that near-ultraviolet and blue LED chips can effectively excite the titled Sm3+-Eu3+ co-doped phosphors. The emission intensity pertaining to Eu3+ ions increases at the expense of decrease in intensity of Sm3+ ions with increase in the concentration of Eu3+ ion in titled Sm-Eu co-doped Sr9Y2W4O24 phosphors. The Reisfeld's approximation applied to the emission spectra of the titled Sm3+-Eu3+ co-doped Sr9Y2W4O24 phosphor reveal quadrupole-quadrupole as the mechanism responsible for energy transfer (ET) from Sm3+ to Eu3+ ions. The PL decay lifetimes values recorded for 603 nm emission of Sm3+ ions under 407 nm excitation wavelength were found to be decreasing with increase in Eu3+ ions concentration. This clearly reveal the ET from Sm3+ to Eu3+ ions in the titled phosphors. With increase in Eu3+ ion concentration the calculated CIE parameters are gradually shifting towards the deep red region of the visible spectrum under UV excitation. The temperature dependent PL (TD-PL) spectra demonstrate that the Sr9Y2W4O24: Sm3+/Eu3+ phosphor has relatively better thermally stablity with its thermal activation energy at around 0.256 eV. The results obtained in the present investigation allows us to explore the utility of Sm3+/Eu3+ co-doped Sr9Y2W4O24 phosphors as an effective deep red emitter needed to fabricate white LEDs.