Achieving Bright Blue and Red Luminescence in Ca2SnO4 through Defect and Doping Manipulation

Designing a bright blue and red phosphor for phosphor-converted white-light-emitting diodes would be extremely beneficial to the lighting industry. Achieving the same through defect and doping engineering in an interesting inorganic layered structure material, Ca2SnO4 (CSO), would fetch a lot of interest among material and optical scientists. There is no report on undoped and doped CSO lattices where extensive effort has been made to understand the origin of host emission, local site occupancy, defect evolution, etc. With the same intention, in this work, we have investigated the photophysical properties of undoped and Eu3+-doped CSO (CSOE). On UV irradiation, CSO displayed beautiful blue emission, and its origin has been explained experimentally using extended X-ray absorption fine structure (EXAFS) and theoretically using density functional theory (DFT) calculations. Both DFT and EXFAS pinpointed the role of oxygen vacancies (OVs) in blue emission of CSO. In fact, by extensive calculations, we also found out that both neutral and charged oxygen vacancies are involved in producing blue emission in CSO. To further tune the luminescence, the Eu3+ ion was doped in CSO, which produces highly pure red emission with an internal quantum efficiency (IQE) of ∼80% and negligible nonradiative transition. Based on EXAFS and lifetime spectroscopy, it was found that the Eu3+ ion is localized in a much higher fraction at the CaO7 site compared to SnO6 octahedra. This was further substantiated using DFT-calculated formation energies. Further, it is expected that aliovalent doping of the trivalent Eu3+ ion at Ca2+/Sn4+ leads to charge-compensating defects, which significantly impact the optical properties of CSOE, and were further investigated using positron annihilation lifetime spectroscopy (PALS). Such complete spectrum of work wherein photophysical properties of functional materials are optimized and studied by deciphering the role of OVs, local site occupancy of the dopant ion, and charge-compensating defects will inculcate a lot of interest within the scientific community in coming forward for research in the area of rare-earth-free phosphor as well as doped phosphor for solving the energy crisis.