Blue-light-excited red emission in a CaO:Eu phosphor

Abstract

Introducing multiple luminescent centers into the matrix crystal is an effective measure to endow this class of materials with new optical properties. Here, the coexistence of Eu²⁺ and Eu³⁺ was achieved in CaO matrix 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 broadband emission at λ_max = 661 nm upon excitation at 466 nm. Calcium vacancies (V_Ca) in CaCO₃:Eu³⁺ increase the reduction rate, thereby enhancing the emission intensity of Eu²⁺. The high Ra (91.2) and LE (49.36 lm/w), and low CCT (3435 K) of as-fabricated WLEDs suggest that the prepared CaO:Eu are promising materials for WLEDs applications. The findings provide a new avenue for exploring novel Eu²⁺-activated simple oxide-based red phosphors.