Violet light excitable KxNa5−xB2P3O13:Eu (x = 0, 1, 2) borophosphates as novel phosphors for multifunctional applications

Abstract

Three novel Eu²⁺-doped blue-emitting phosphate phosphors, K_xNa_5−xB₂P₃O₁₃ (x = 0, 1, 2), were successfully synthesized via a conventional high-temperature solid-state reaction method. The phase purity, crystal structure, morphological characteristics, and photoluminescence properties of these phosphors were systematically investigated. X-ray diffraction (XRD) analysis confirmed the effective substitution of Na⁺ lattice sites by Eu²⁺ ions in all three host matrices. The excitation spectra exhibited broad absorption bands ranging from 250 to 400 nm, indicating efficient excitation compatibility with ultraviolet (UV) light sources. Blue emission originating from the 4f–5d electronic transitions of Eu²⁺ was observed, with peak wavelengths progressively red-shifting from 436 nm (Na₅B₂P₃O₁₃) to 450 nm (KNa₄B₂P₃O₁₃), and 448 nm (KNa₄B₂P₃O₁₃) as potassium content increased. Optimal photoluminescence performance was achieved at Eu²⁺ doping concentrations of 1 mol%, 2 mol%, and 3 mol% for Na₅B₂P₃O₁₃, KNa₄B₂P₃O₁₃ and KNa₄B₂P₃O₁₃, respectively. Dipole–dipole interaction is the main mechanism of concentration quenching in phosphors. To demonstrate practical applicability, the optimized phosphors (Na₅B₂P₃O₁₃:0.01Eu²⁺, KNa₄B₂P₃O₁₃:0.02Eu²⁺, and K₂Na₃B₂P₃O₁₃:0.03Eu²⁺) were integrated with commercial Lu₃Al₅O₁₂:Ce³⁺ (LuAG) phosphor, CaAlSiN₃:Eu²⁺ red phosphor, and UV LED chips to fabricate white light-emitting diodes (WLEDs). The resulting devices exhibited high color rendering indices (Ra) of 82.3, 91.6, and 90.6, respectively. These novel phosphors demonstrate significant potential for WLED and thermal sensor applications, relatively low synthesis temperatures (compared to conventional blue phosphors), and cost-effective raw material requirements.