Difference in the Nature of Eu 3+ Environment in Eu 3+ -Doped BaTiO 3 and BaSnO 3 Dinesh K. Patel, ‡ Bathula Vishwanadh, § Vasanthakumaran Sudarsan, ‡ and Shailendra K. Kulshreshtha ‡,† ‡ Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India § Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400085, India BaTiO 3 and BaSnO 3 samples doped with Eu 3+ ions were prepared using glycine-nitrate gel combustion method. Relative intensities and line shapes of magnetic dipole allowed 5 D 0 ? 7 F 1 and electric dipole allowed 5 D 0 ? 7 F 2 transitions of Eu 3+ from the hosts, BaTiO 3 and BaSnO 3 , are significantly different. Based on detailed structural investigations, it is confirmed that synthesizedBaTiO 3 sample is tetragonal with no center of sym- metry around Ba 2+ ions. Unlike this BaSnO 3 is cubic with centrosymmetric Ba 2+ site. From X-ray diffraction and experi- mentally obtained Judd–Ofelt parameters (Ω 2 and Ω 4 values), it is confirmed that in BaTiO 3 there is a decrease in the aver- age Ba–O and Ba–Ba distances compared with that in BaSnO 3 . This leads to higher Eu–O bond polarizability and adds to the distortion in its environment around Eu 3+ in BaTiO 3 :Eu compared with BaSnO 3 :Eu. This is responsible for the observed difference in the luminescence properties. I. Introduction BATiO 3 and BaSnO 3 belong to the category of materials having perovskite structure and have potential applications in the field of microwave devices and thermally stable capaci- tors. 1–5 BaTiO 3 exists in five crystalline forms namely rhom- bohedral, orthorhombic, tetragonal, cubic, and hexagonal forms. The tetragonal form of BaTiO 3 is ferro-electric and undergoes phase transition to para-electric cubic phase around 132°C. The cubic phase is quite stable up to 1200°C and above. Unlike this, Barium stannate (BaSnO 3 ) exists in cubic structure with high thermal stability up to its melting temperature of 2060°C. 4,5 BaTiO 3 and BaSnO 3 are also potential hosts for doping lanthanide ions and these doped materials have many applications such as integrated light emitting devices, field-emission displays, lasers, positive coef- ficient resistors, etc. 6–9 Many reports are available on the optical properties of lanthanide-ions-doped BaTiO 3 and BaS- nO 3 materials. As Eu 3+ luminescence with respect to differ- ent structural environments is well understood, it is often used as a probe lanthanide ion to understand the structural changes, occurring at the doping site. For example, Pazik et al. 10 have observed that emission spectrum form nanocrys- talline BaTiO 3 :Eu 3+ powders, prepared by microwave-stimu- lated hydrothermal method, are dominated by the electric dipole allowed 5 D 0 ? 7 F 2 transition. The multiexponential decay curves corresponding to 5 D 0 level of Eu 3+ ions observed from the samples have been attributed to the com- bined effect of disorder around Eu 3+ sites in the lattice as well as the energy transfer among different Eu 3+ ions. Exis- tence of distorted environment around Eu 3+ ions in nano- crystalline BaTiO 3 and thin films has also been reported by different groups. 11,12 Similarly optical properties of BaSnO 3 both undoped and doped with luminescent lanthanide (Ln 3+ ) ions like Eu 3+ , Tb 3+ , etc., have also been investi- gated. 13–16 Lu et al. 14 have studied the luminescence proper- ties of CaSnO 3 :Eu, SrSnO 3 :Eu, and BaSnO 3 :Eu particles, having size in the range 350 nm, and concluded that CaS- nO 3 :Eu sample gives more intense red emission characteristic of Eu 3+ ions, compared with BaSnO 3 :Eu sample. This has been attributed to the orthorhombic crystal structure of CaS- nO 3 and associated lower symmetry around Ca 2+ /Eu 3+ ions compared with cubic BaSnO 3 :Eu, where Eu 3+ ion is having a more symmetric environment. Recently, Pang et al. 17 have carried out detailed upconversion luminescence studies on ASnO 3 nanoparticles (where A = Ca 2+ , Sr 2+ , and Ba 2+ ) doped with Er 3+ ions. These authors observed that emission intensities are quite weak for BaSnO 3 :Er nanoparticles as compared with SrSnO 3 :Er and CaSnO 3 :Er nanoparticles. This is again explained based on the cubic nature of the BaS- nO 3 phase and symmetric crystal field around the Ba 2+ /Er 3+ ions in the lattice. In conformity with earlier studies mentioned above, our studies on Eu 3+ -doped BaTiO 3 and BaSnO 3 , have revealed that the Eu 3+ luminescence characteristics (lifetime values, asymmetric ratios of luminescence, and line shapes) are quite different in both the samples, even though Eu 3+ occupy Ba 2+ site in BaTiO 3 and BaSnO 3 . It is worth mentioning here that exactly identical preparation conditions with same doping level have been used to prepare both the samples. The observed difference in the luminescence properties prompted us to investigate the structural aspects of these samples. This article throws light on the changes in the elec- tronic environment around a luminescent species such as Eu 3+ brought about by structural differences present in the host lattice. II. Experimental Procedure (1) Preparation of Eu 3+ -Doped BaTiO 3 and BaSnO 3 Samples (A) Reagents Used: Analytical grade reagents of bar- ium nitrate, Ti-isopropoxide, Tin metal, europium nitrate, and glycine were used as starting materials for the prepara- tion of Eu 3+ -doped BaTiO 3 and BaSnO 3 samples. (2) Preparation of BaTiO 3 :Eu and BaSnO 3 :Eu Samples For preparing BaTiO 3 :Eu 3+ (2%) and BaSnO 3 :Eu 3+ (2%) samples, glycine-nitrate combustion method was used. In a typical procedure for the preparation of BaTiO 3 doped with 2 at.% Eu 3+ ions, around of 0.87 g Ba(NO 3 ) 2 , required amount of Eu 3+ in aqueous solution and 1 g of glycine were J. McKittrick—contributing editor Manuscript No. 33048. Received April 16, 2013; approved August 11, 2013. † Author to whom correspondence should be addressed. e-mail: kulshres@gmail.com 3857 J. Am. Ceram. Soc., 96 [12] 3857–3861 (2013) DOI: 10.1111/jace.12596 © 2013 The American Ceramic Society J ournal