Enhanced red luminescence of Ca₃Si_2−xM_xO₇:Eu³⁺ (M = Al, P) phosphors via partial substitution of Si⁴⁺ for applications in white light-emitting diodes

A red-emitting phosphor Ca_2.91Si₂O₇:0.09Eu³⁺ with partial Al³⁺/P⁵⁺ substitution on Si⁴⁺ was synthesized via a simple solid-state method, and the effects of the introduction of the M^3+/5+ (M = Al, P) ions on the crystal structure and photoluminescence performance of Ca_2.91Si_2−xM_xO₇:0.09Eu³⁺ phosphors were investigated. The X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) results revealed that the structure of Ca₃Si₂O₇ remained the same after the introduction of Al³⁺ and P⁵⁺ ions. The characteristic emission of Eu³⁺-doped Ca₃Si_2−xM_xO₇ phosphors exhibited two main peaks at 617 nm (red) and 593 nm (orange) under excitation at 394 nm, which originated from the ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₁ electron transitions of Eu³⁺ ions. After the partial substitution of Al³⁺ and P⁵⁺, the red emission intensities of the Ca_2.91Si₂O₇:0.09Eu³⁺ phosphors were significantly enhanced by 1.88- and 1.42-fold, respectively, which is attributed to the crystal-field effect around Eu³⁺. Meanwhile, the luminescence intensities of the Ca_2.91Si_1.96Al_0.04O₇:0.09Eu³⁺ and Ca_2.91Si_1.94P_0.06O₇:0.09Eu³⁺ phosphors at 210 °C were 79.36% and 77.53% of those at 30 °C, respectively, indicating their excellent thermal stability. Moreover, the as-prepared Ca_2.91Si_1.96Al_0.04O₇:0.09Eu³⁺ and Ca_2.91Si_1.94P_0.06O₇:0.09Eu³⁺ red-emitting phosphors were combined with a near-ultraviolet chip of 395 nm to fabricate red-light-emitting diode (LED) and white (w)-LED devices with excellent chromaticity features. In summary, Al³⁺/P⁵⁺-substituted Ca_2.91Si₂O₇:0.09Eu³⁺ can serve as red-emitting phosphors for applications in w-LEDs.