Blue-Light-Excited Red Emission in a Cao:Eu Phosphor

Abstract

Introducing multiple luminescent centers into crystals is an effective way to endow this class of materials with new optical properties. Here, the coexistence of Eu2+ and Eu3+ was achieved in CaO crystal from CaCO3:Eu3+ by a double crucible carbon reduction method. Under NUV-light excitation, the PL spectrum of CaO:Eu consists both a broad band of Eu2+ and several sharp lines of Eu3+. More significantly, CaO:Eu exhibits a broad emission band at λmax=661 nm when excited at 466 nm. There exists a rare energy transfer from Eu3+ to Eu2+ in CaO:Eu. Calcium vacancies (VCa ) in CaCO3:Eu3+ increase the reduction rate and thus intensity of Eu2+ emissions. The high color-rendering index Ra (91.2) and luminous efficacy (49.36 lm/w), and low CCT (3435 K) of as-fabricated WLEDs clearly demonstrate the prepared CaO:Eu are promising materials for WLEDs applications. The findings provide a new perspective for the exploration of novel Eu2+ activated simple oxide-based red phosphor for pc-LEDs.

Keywords: CaO, Eu2+, Blue-light-excited, Red emission, WLED