Role of La3+ ion substitution sites on the photoluminescence properties of the SrTiO3 :Eu3+ phosphors

The consequence of the site selective substitution of La3+ ions in modifying the local crystal structure in red emitting titanate perovskites and the resulting enhancement of the luminescence properties were investigated in two distinct series of red phosphors of Sr1-x-yLaxTiO3:yEu(3+) and Sr1-x/2-yLaxTi1-x/2O3:yEu(3+). Herein, the red emission line was found sharply magnified for the substitutions at the Sr2+ sites whereas broad peaks resembling the emission from the La2O3 :Eu3+ red phosphor were detected for the substitution at both Sr2+ and Ti4+ sites, in the experiment of altering substitution sites of the La3+ ions in Sr1-xTiO3:xEu(3+). The local asymmetry induced by the substitution of smaller aliovalent ions was found to enhance the luminescence properties in the phosphors with doping at the Sr2+ sites. The occupation of Eu3+ ions in an environment having La3+ ions as nearest neighbours relaxes the shielding of the 4f electrons of Eu3+ to produce a broad emission in the phosphors with double site doping. The substitution of rare earth ions at the Sr2+ sites in Sr1-x-yLaxTiO3:yEu(3+)was verified by the enhancement in the intensity of the Raman modes at 184 cm(-1) (TO2) and 476 cm(-1) (LO2). In the case of the Sr1-x/2-yLaxTi1-x/2O3:yEu(3+) phosphors, the presence of the substituent ions at the Ti4+ sites was confirmed by the increased intensity observed for the Raman mode at 114 cm(-1) (TO1). (C) 2020 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.