A simple approach to generate efficient white light emission from a ZnO–ionic liquid complex

A simple method has been described for the generation of white light from cationic ionic liquid (IL) compounds 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF<SUB>4</SUB>) stabilized ZnO nanocrystals (NCs). Upon mixing of the IL with the ZnO NCs, the absorption band is red shifted from 245 nm to 285 nm which is attributed to the charge-transfer band due to donor–acceptor systems. The blue emission band at 420 nm for pure IL is originated from the π–π* transition in the imidazolium moiety and the strong yellow band at 557 nm is due to the defect emission of the ZnO NCs. In the case of ZnO NCs in the IL, the combination of the blue emission from the ionic liquid and the yellow emission from ZnO gives intense white light. Control experiments have been done with varying concentration of IL and ZnO NCs to understand the best conditions for efficient white light generation. The maximum quantum efficiency of the white light emission was found to be 4.7%