Blue-Emitting Phosphors M₂P₂O₇:1%Eu²⁺ (M = Ca, Sr, Ba) Pyrophosphates for LED Lighting

In this book chapter, the divalent europium-activated alkaline-earth-metal pyrophosphate M₂P₂O₇ (M = Ca, Sr, Ba) phosphors were effectively prepared via a conventional high temperature sintering reaction technique in a reducing atmosphere at 900 ℃. The synthesized materials have been systematically investigated using powder X-ray diffraction. The XRD pattern exhibit that Ca₂P₂O₇ has a β-phase, Sr₂P₂O₇ has an α-phase, Ba₂P₂O₇ has a β-phase and the crystal structure of the M₂P₂O₇ (M = Ca, Sr, Ba) hosts was unaffected with the introduction of Eu²⁺ ions. The nuclear magnetic resonance (NMR), infrared (IR) and Raman spectroscopy of β-Ca₂P₂O₇, α-Sr₂P₂O₇ and γ-Ba₂P₂O₇ were reported and discussed in accordance with the structural peculiarities of Alkaline earth phosphates. The luminescence properties of Eu²⁺ in these phosphate materials were explored in detail in both vacuum ultraviolet (VUV) and ultraviolet (UV) regions. The emission spectra of β-Ca₂P₂O₇: 1%Eu²⁺, α-Sr₂P₂O₇: 1%Eu²⁺ and γ-Ba₂P₂O₇:1%Eu²⁺ exhibit a large asymmetric band blue-emitting under the excitation of 320 nm, caused by the 4f⁶5d¹ → 4f⁷[⁸S_7/2] transition of Eu²⁺ at room temperature. The excitation spectra display a broad and intense absorption in the 250–400 nm wavelengths region, which is matched with the blue emission band using for emitting n-UV (NUV) LED chips (360–400 nm). The above results indicate that diphosphate phosphors could be promising for generating blue-materials for white LED applications.