A single-phased emission-tunable phosphor Ca₉Y(PO ₄)₇:Eu²⁺,Mn²⁺ with efficient energy transfer for white-light-emitting diodes

series of single-composition emission-tunable Ca₉Y(PO ₄)₇:Eu²⁺,Mn²⁺ phosphors were synthesized by solid-state reaction. The energy transfer from Eu²⁺ to Mn²⁺ in Ca₉Y(PO₄)₇ host matrix was studied and demonstrated to be a resonant type via a dipole-quadrupole mechanism with the critical distance of ∼ 11 A°. The wavelength-tunable white light can be realized by coupling the emission bands centered at 486 and 638 nm ascribed to the contribution from Eu²⁺ and Mn²⁺, respectively. By properly tuning the relative composition of Eu ²⁺/Mn²⁺, chromaticity coordinates of (0.31, 0.33) can be achieved under excitation at 250-440 nm. Moreover, white-light-emitting diodes were fabricated through the integration of 365 nm chips and single composition white-light- emitting phosphors (Ca_0.975Eu₀₀₁Mn _0.015)₉Y(PO₄)₇ into a single package shows a cool white light of 7200 K, color rendering index of 76, and color coordinates of (0.30, 0.31) close to that of ideal white light can be achieved.