Local Environments Around Eu3+ and Eu2+ Ions in Dual Light-Emitting BaSnO3:Eu Nanomaterials

The change in the environment around Eu3+ and Eu2+ 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 (Eu3+ and Eu2+) occupy the centrosymmetric Ba2+ sites up to 4 atom-% in BaSnO3, beyond which it forms a separate europium oxide phase with both Eu2+ and Eu3+ ions. There is energy transfer from the BaSnO3 host to the Eu2+ 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(T2g)?4f 7(8S7/2) transition of Eu2+ (480 nm) and intra-4f transitions of Eu3+ (590 and 612 nm) have been observed. For samples that contain more than 4 atom-% europium ions based on steady-state luminescence measurements and lifetime values that correspond to the 5D0 level of Eu3+ ions, it is inferred that there are mainly three types of Eu3+ ions: the first at Ba2+ sites with perfect dodecahedral geometry in the bulk of the nanomaterials, the second at Ba2+ 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 Eu2+ species.