White light-emitting ZnO nanoparticles exhibiting color temperature tunability with near UV excitation and high color rendering

Abstract

The development of high-quality white-light phosphor for lighting and their facile synthesis is highly desired. Achieving white-light emission in undoped metal-oxides is in great demand, and hence ZnO being a potential phosphor was explored. However, tailoring defect-oriented emissions that mainly depend on processing conditions is challenging. Annealing effects on ZnO to obtain white-light with completely diminished near band-edge emission is detailed here. A systematic variation of processing temperature, ambient pressure, and ambient gas helped tailor the white-light emission. Optimized ZnO nanophosphors emitted white-light with the near-ideal Commission International de l’Eclairage (CIE) coordinates (x = 0.32, y = 0.33 at λex = 325 nm) and correlated color temperature (CCT) of 6200 K (corresponding to day white-light). Optimized processing conditions achieved neutral white-light (x = 0.33, y = 0.33 at λex = 340 nm) and CCT 5645 K. ZnO nanoparticles exhibit excellent color rendering index (CRI) of >90 and high R9 values up to 97%, essential in efficiently rendering object colors compared to that under sunlight. Phosphor-converted white light-emitting diodes (pc-WLEDs) were fabricated on commercial LEDs using the prepared ZnO nanophosphors. pc-WLEDs emitted neutral and day white-light, well-suited for indoor solid-state lighting devices.