Ca₃Al₂(SiO₄)_{3- δ}Cl_4δ:Eu²⁺, Mn ²⁺: A potential phosphor with energy transfer for near-UV pumped white-LEDs

A series of Eu²⁺ and Mn²⁺ coactivated Ca ₃Al₂(SiO₄)_{3- δ}Cl_4δ phosphors have been synthesized by solid state reactions and their luminescence properties have been investigated by means of powder diffuse reflection, photoluminescence excitation and emission spectra, and lifetimes. The phosphor Ca ₃Al₂(SiO₄)_{3- δ}Cl_4δ:Eu²⁺, Mn ²⁺ exhibits two dominating bands situated at 460 and 550 nm, originate from the allowed 5d → 4f transition of the Eu²⁺ ion and the ⁴T_1g(4G) → ⁶A_1g(6S) transition of the Mn²⁺ ion, respectively. We have discovered that energy transfers from Eu²⁺ to Mn²⁺ by directly observing significant overlap of the excitation spectrum of Mn²⁺ and the emission spectrum of Eu²⁺ as well as the decline of lifetimes of Eu²⁺. By utilizing the principle of energy transfer, we have demonstrated that with appropriate tuning of activator content Ca ₃Al₂(SiO₄)_{3- δ}Cl_4δ:Eu²⁺, Mn ²⁺ phosphors exhibit potential to act as a phosphor for near ultraviolet light-emitting diodes.