Energy transfer properties of a single-phase Na3Gd(PO4)2:Eu2+,Mn2+ phosphor with excellent thermal stability for w-LEDs

Abstract

A high temperature solid state method was used to prepare Na₃Gd(PO₄)₂:Eu²⁺,Mn²⁺ phosphors with good thermal stability. The phosphor shows a broadband excitation region of 250–430 nm, which can be matched with the emissions of ultraviolet (UV)/near-ultraviolet (NUV) LED chips for white light emitting diodes (w-LEDs). The energy transfer efficiency is 74.46% from the sensitizer Eu²⁺ ions to the activator Mn²⁺ ions, which enhances the intensities of the Na₃Gd(PO₄)₂-based phosphor. In addition, by increasing the Mn²⁺ doping level in the phosphor, the Na₃Gd(PO₄)₂:Eu²⁺,Mn²⁺ phosphor first shows blue light, then turns to white light, and finally emits red light under 365 nm excitation. Besides, the temperature-dependent photoluminescence measurements indicate that the prepared phosphors exhibit good thermal stability. W-LEDs fabricated by combining a 365 nm chip with the Na₃Gd(PO₄)₂:Eu²⁺,Mn²⁺ phosphor exhibit bright white light, which has a high color rendering index (CRI) = 91.5, and a relatively low correlated color temperature (CCT) = 5198 K. Moreover, the CIE point is calculated to be at (0.3337, 0.3465), which is located in the white light region. These results indicate that the as-prepared phosphors can be considered as potential candidates for UV/NUV light-excited w-LED applications.