The change in the environment around Eu ³⁺ and Eu ²⁺ species as a function of their concentration in BaSnO₃:Eu nanomaterials has been investigated by low-temperature (77 K) luminescence and electron paramagnetic resonance (EPR) spectroscopy. These materials show dual emission from the europium ions upon single-wavelength excitation. Europium ions (Eu ³⁺ and Eu ²⁺ ) occupy the centrosymmetric Ba²⁺ sites up to 4 atom-% in BaSnO₃, beyond which it forms a separate
europium oxide phase with both Eu ²⁺ and Eu ³⁺ ions. There is energy transfer from the BaSnO₃ host to the Eu ²⁺ ions in the samples. Upon single-wavelength UV excitation (280 nm) of the BaSnO₃:Eu nanomaterials, strong emissions at 430, 480, 590 and 612 nm, characteristic of exciton recombination in the host BaSnO₃ (430 nm), the 4f⁶5d¹(T_2g)→4f ⁷(⁸ S _7/2) transition of Eu ²⁺ (480 nm) and intra-4f transitions of Eu ³⁺ (590 and 612 nm) have been observed. For samples that contain more than 4 atom-% europium ions based on steadystate luminescence measurements and lifetime values that correspond to the ⁵ D₀ level of Eu ³⁺ ions, it is inferred that there are mainly three types of Eu ³⁺ ions: the first at Ba ²⁺ sites with perfect dodecahedral geometry in the bulk of the nanomaterials, the second at Ba ²⁺ sites at the surface of the nanomaterials and the third type as a separate europium oxide phase. Similarly, EPR specroscopy confirms the presence of three types of environments for the Eu ²⁺ species