Add time:08/31/2019         Source:sciencedirect.com

Optical characteristics of a doped material depend on the site wherein the dopant resides. In mixed A-site perovskites, the dopant has several possibilities. This, in turn, correlates with the emission spectrum of the doped material. Here we choose Eu3+ as the dopant since it is a well-known and efficient red-luminophore. Sodium bismuth titanate (NBT-Na0.5Bi0.5TiO3) is selected as a host due to its ability to accommodate Eu over large concentration windows while maintaining optical activity. For compositions x ≥ 0.04, we show that Eux:NBT has amphoteric behavior (i.e., simultaneous dopant substitution in two competing sites). Eu3+ occupancy in Bi and Ti-sites are quantitatively estimated using Rietveld refinement. Also, the appearance of A1g breathing vibrational mode (830-860 cm−1) in Raman spectra shows the presence of Eu3+ on the Ti-site. Photoluminescence (PL) emission shows sharp and intense bands at ∼592 nm, ∼615 nm, and ∼687 nm, and one weak band at ∼652 nm, corresponding to f-f transitions of Eu3+. To evaluate the optical characteristics with varying site-substitution of Eu3+; Judd-Ofelt parameters and radiative properties are calculated for the first time in this mixed A-site titanate system. From the values of asymmetric ratios; Eu3+ ion is shown to occupy the non-centrosymmetrical sites (Bi-sites) of NBT. However, at x = 0.04, Ω2 < Ω4, which indicates long-range effects and hence Eu occupancy in centrosymmetric sites (Ti-sites). This study opens up avenues for further exploration of correlations between dopant-concentration, amphotericity, and spectrochemical response in other systems. The amphoteric behavior of dopants can tune emission intensities and produce multi-emission colors using a single-dopant. This would have implications for luminescence-based applications.

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