Luminescence and theoretical calculations of novel red-emitting NaYPO₄F:Eu³⁺ phosphor for LED applications

A novel red-emitting garnet NaYPO4F:Eu³⁺ phosphor was synthesized by a high-temperature solid-state method. The crystal structure, emission/excitation spectra, as well as decay curves and thermal stability were investigated in this paper. The excitation spectra varied with the Eu³⁺ concentration and consisted of one broad and three sharp intense, and several weak peaks. The broad band was assigned to the Eu³⁺−O^2- charge transfer band (CTB) and this CTB has a continuous red-shift with increasing Eu³⁺ concentration. The sharp bands are related to the 4f−4f transitions of Eu³⁺ ions in the host lattice. The emission spectra show that the dominated peak at 609 nm corresponds to the ⁵D₀ → ⁷F₂ transitions of Eu³⁺. The optimal Eu³⁺-doped concentration in NaYPO₄F was found to be 20 at%. The luminescence decay lifetimes of NaYPO₄F:xEu³⁺ phosphors were in the range of 2.43 to 1.74 ms. The thermal stability indicated that the luminescence only decay 21% at 150 °C and decay 35% at 250 °C, respectively.