Probing emission and defects in BaW1-xMoxO4 solid solutions: Achieving color tunable luminescence by W/Mo ratio and size manipulation

Structure, size, and defect manipulation have been found to be one of the highly effective strategy in tuning the properties of optical functional materials. To investigate the same; nano and bulk counterparts of Eu3+ doped scheelite BaW1-xMoxO4 solid solutions were synthesized and their optical properties were investigated. Positron annihilation lifetimes were found to be larger in ‘as prepared’ nano samples compared to bulk suggesting more defects in nano samples. The positron lifetimes increased on Eu3+ doping, suggesting creation of more defects with possibilities being W/Mo occupying Ba2+ site or co-inclusion of Na+ for charge compensation. Inclusion of Mo inhibits host to dopant (Eu3+) energy transfer (HDET) in bulk sample but very efficient HDET happens in nano samples. Higher degree of asymmetry around Eu3+ in nano compared to bulk samples was observed and attributed to the large defects density as well as the relaxations around the defects in the former, and this is also manifested as lower unit cell volume. It is found that doped nano scheelites of BaW1-xMoxO4 can be used as red phosphor while the bulk sample can be used as color tunable phosphor in red, orange, yellow and near white luminescence applications by varying the composition. This work has really projected the importance of defect and doping manipulation on optical properties of undoped and doped, pure and mixed tungstate-molybdate system.