CaY2Al4SiO12:Ce3+,Mn2+: a single component phosphor to produce high color rendering index WLEDs with a blue chip

Abstract

A high color rendering index white light emitting diode (WLED) is generally produced by combining yellow and red mixed phosphors on a blue chip. Herein we report a single component phosphor based on CaY₂Al₄SiO₁₂ (CYAS) to achieve warm white light emission with a high color rendering index (R_a), which can be up to 90.5. Ce³⁺, Mn²⁺ singly doped and co-doped CYAS phosphors have been synthesized by solid state reactions, respectively, for comparative investigations. The Rietveld X-ray diffraction (XRD) refinements show that the CYAS host crystallizes in a cubic structure with the Iad space group. The valence states of Ce and Mn inside the CYAS host have been confirmed by XPS and EPR. Ce³⁺ occupies the Ca²⁺/Y³⁺ site and generates a yellow emission band around 543 nm from its characteristic 5d–4f transition. Mn²⁺ occupies both the dodecahedron Ca²⁺/Y³⁺ and octahedral Al³⁺ sites, emitting red and deep red lights at 616 nm and 750 nm, respectively. These two emission bands are attributed to the ⁴T₁(⁴G)–⁶A₁(⁶S) transitions of Mn²⁺. Upon 460 nm light excitation, both the Ce³⁺ and Mn²⁺ characteristic emissions can be obtained, in which the emissions of Mn²⁺ result from the occurrence of energy transfer from Ce³⁺ in CYAS. All the results indicate that the prepared CYAS:Ce³⁺,Mn²⁺ could be a promising single component phosphor for blue chip WLEDs.