Double perovskite antimonates of the type BaLaMSbO 6 (M=Mg, Ca) were synthesized by a standard solid-state route. The compounds were characterized by X-ray crystallography and the structures were refined using Rietveld method. BaLaMgSbO 6 and BaLaCaSbO 6 crystallized in monoclinic space groups (I2/m) and (P2 1 /n), respectively. In both compounds, La occupied the A-site of perovskite, which is 12-coordinated as compared to Ba 2 LaSbO 6 where La ion shifts to the B-site octahedral coordination due to the larger size of Ba as compared with Mg and Ca. The samples were further characterized using FTIR and the frequency of the octahedral vibration is correlated to the electronegativity of the B-site ions. Photoluminescence study of the title compounds and Ba 2 LaSbO 6 was carried out upon doping with 2 atom% Eu 3 + ion, which confirmed that Eu 3 + occupies distorted 12-coordinated A-site in BaLaMSbO 6 (M=Mg, Ca) and symmetrical octahedral B-site in Ba 2 LaSbO 6 . Furthermore, the emission spectrum corresponding to each Eu 3 + ion at different crystal site was successfully isolated through a TRES study. This site selective occupancy of Eu 3 + ion also has a direct impact on the light emission, which was found to change from orange to red in a dark room in the order Ba 2 LaSbO 6 : Eu! BaLaCaSbO 6 : Eu!BaLaMgSbO 6 : Eu. Such an outcome will have high impact in designing new commercial Eu 3 + ion doped phosphor materials and tailoring of their optical properties.

Niobates of the formula Ba2LaNbO6 and BaLaM2+NbO6 (M2+ = Mg, Ca) were synthesized by the conventional solid state route. Size dependence of M‐cation on the bulk crystal structure of BaLaM2+NbO6 was studied and compared with the Ba2LaNbO6 compound. X‐ray diffraction study confirmed that BaLaMgNbO6 compound has the rhombohedral (R3¯) crystal structure as compared to the monoclinic (I2/m) in BaLaCaNbO6 and Ba2LaNbO6. The change in the local structure of La cation among these compounds was investigated by carrying out Photoluminescence study on 2 atom% Eu3+‐doped samples. PL study of BaLaMgNbO6:Eu3+ sample indicates Eu3+ ions occupying the distorted 12‐coordinated A‐site, while in Ba2LaNbO6: Eu3+, Eu3+ is present at highly symmetric octahedral B‐site. Upon excitation, the light emission of these compounds changes from reddish‐orange to red to purple in the order Ba2LaNbO6:Eu → BaLaCaNbO6:Eu → BaLaMgNbO6:Eu3+, due to change in Eu3+‐ions site occupancy. Lifetime study also confirmed the presence of two different Eu3+ components at two different lattice sites and their respective emission spectra were isolated by time resoled emission spectroscopy. Furthermore, this site selective lattice occupancy of Eu3+ ions also gave various new insights about its radiative and nonradiative properties at different lattice sites. This works presents a complete structural understanding of BaLaMNbO6‐based matrices and their versatile phosphor characteristics when doped with Eu3+ ion.

Chloroform soluble luminescent undoped and europium doped LaPO4 nanoparticles (NPs) were synthesized by oleic acid mediated solvothermal technique at low temperature (150 °C). These NPs have nanorod (NR) shape as confirmed by Transmission electron microscopy (TEM) and monoclinic phase as confirmed by X‐ray diffraction (XRD) measurement. Fourier transform infrared (FTIR) studies shows that oleic acid is bound to the surface of NRs. The Photoluminscence (PL) spectroscopy suggests that the undoped LaPO4 emits violet blue light when excited by UV‐light due to the surface oleate groups. In the doped NRs, oleate group serves as a sensitizer for the surface Eu3+ ions. In order to increase the emission output of these NRs, 2‐theonoyltrifluoroacetonate (TTA) is used to sensitize the emission of surface Eu3+ ions. PL spectroscopy and lifetime measurements clearly show that sensitization takes place only on the surface of the NRs while the core Eu3+ ions remains unsenesitized. The emission output is increased 33 times as compared to the unsensitized NRs. Further, these NRs were transferred from organic to the aqueous phase by citric acid. The NPs thus obtained are redispersible in water with good colloidal stability. Here, also sensitization of surface europium ions occurs in aqueous solution by TTA ligand. These luminescent organic and water soluble NRs further strengthen the application in the fields of optical display, lighting and bioimaging.

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