Light Harvesting from Oxygen Vacancies and A- and B-Site Dopants in CaSnO3 Perovskite through Efficient Photon Utilization and Local Site Engineering

Abstract

Significant research has been carried out in ABO3 perovskites during last decades in tailoring their luminescence properties for advanced optoelectronics. However, research related to exploring contribution of defects, both cation and anion vacancies in photoluminescence for multicolor photon emission has never been explored. Here, in this work, we have harnessed the full gamut of light emission from violet-blue to deep red originating from oxygen vacancies (OVs) in undoped CaSnO3 (CSO) and Eu@CaO8 and Eu@SnO6 sites in the doped CaSnO3:Eu3+ (CSOE) perovskite. Any contribution of Sn2+ and Eu2+, respectively, in photoluminescence of CSO and CSOE has been completely ruled out through X-ray absorption near-edge structure. Synchrotron radiation-based extended X-ray absorption fine structure and positron annihilation lifetime spectroscopy showed simultaneous distribution of Eu3+ ions at both asymmetric CaO8 and symmetric SnO6 sites owing to a very high negative formation energy value of −6.56 eV for the same. By efficient photon utilization arising from two different charge transfer bands, axial oxygen of SnO6 octahedra O1 → Eu3+ CTB (∼250 nm) preferentially transfers energy to Eu@CaO8 leading to intense electric dipole transition, whereas equatorial oxygen of SnO6 octahedra O2 → Eu3+ CTB (∼300 nm) excites Eu@SnO6 leading to intense magnetic dipole transition. This analogy is confirmed by DFT, wherein it was found that the calculated energy difference between the valence band maxima and conduction band minima is 4.77 eV (∼250 nm) and 4.3 eV (∼300 nm) for Eu@Ca and Eu@Sn sites, respectively. This concept of site-selective excitation and local site engineering can be applied to a variety of optical materials, which provides a unique strategy for tuning other properties of multifunctional crystals that are highly sensitive to the dopant’s local environment.