Perovskite titanates at the nanoscale: Tunable luminescence by energy transfer and enhanced emission with Li+ co-doping

Abstract

Three series of highly luminescent Ca1-xTiO3:xDy3+, Ca0.98-yDy0.02TiO3:yEu3+ and Ca0.91-zDy0.02Eu0.07TiO3:zLi+ nanophosphors have been synthesized by solution combustion method. X-ray diffraction analysis and Rietveld refinements of these phosphors confirms the pnma (62) structure and the occupancy of substituent ions in the matrix. Increase in intensity of the Raman modes viz., O–Ti–O bending mode (249 ​cm−1) and local vibrational mode (800 ​cm−1) signifies the occupancy of rare earth ions in the lattice. XPS analysis verifies the change in coordination environment around the RE3+ ions due to the variation in electron density by the observed shift in binding energy corresponding to the chemical states of Dy 3d and Eu 3d when Li+ ions are codoped. Ca1-xTiO3:xDy3+ exhibits a luminescence close to standard white and tuning of correlated color temperature is achieved by varying the excitation wavelength. In Ca0.98-yDy0.02TiO3:yEu3+ phosphors, co-doping of Eu3+ enables red component in white emission and at higher concentration of Eu3+, emission changes from orange red to purplish red, when wavelength of excitation is altered from 366 to 388 ​nm by virtue of energy transfer mechanism. An enhancement of luminescence intensity by 2.1 times has been observed due to Li+ substitution at optimum concentration in Ca0.91-zDy0.02Eu0.07TiO3:zLi+. This evidences the role of Li+ ions in modifying the crystal field interaction in perovskite luminescent materials.