Emission tunable of Mg0.695Si0.695Al1.39O3.65N0.35:Eu2+,Mn2+ oxynitride phosphors via energy transfer for WLEDs

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

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.

Tailored Luminescence Output of Bi3+-Doped BaGa2O4 Phosphors with the Assistance of the Introduction of Sr2+ Ions as Secondary Cations

In this work, a tunable luminescence color from yellow to orange of photoluminescence (PL), long persistent luminescence (LPL), and photostimulated luminescence (PSL) is successfully achieved in BaGa₂O₄:Bi³⁺ phosphors with the introduction of Sr²⁺ ions as secondary cations. It is confirmed that broad-band emissions located at 500 and 600 nm originate from the occupation of Bi³⁺ ions at different lattice sites in the BaGa₂O₄ host matrix. The replacement of Sr²⁺ for Ba²⁺ ions makes the emission red-shift from 600 to 650 nm; moreover, two additional emissions appeare at 743 and 810 nm due to the occupational preference of Bi³⁺ ions at Ga³⁺ sites. Furthermore, the doped Sr²⁺ ions promote the reconstruction of the trapping centers, which conduces to the fundamental improvement of the optical storage capacity behavior of Bi³⁺-doped phosphors. Our results clarify the dependence of the luminescence performance on the crystal sites of Bi³⁺ ions with fascinating broad-band emissions in the BaGa₂O₄:0.01Bi³⁺ host matrix and will benefit the design and exploration of Bi³⁺-doped solid solutions for optical storage applications.