Spectroscopic investigation of the novel orange-red phosphor Ca3La2W2O12:Sm3+ with the high color purity for w-LED applications

Abstract

A series of novel orange-red emitting tungstate phosphors, Ca3La2W2O12 (CLWO):xSm3+ (0.005 ≤ x ≤ 0.30) were successfully prepared through the solid-state method at high temperature. The space group is hexagonal R3‾m. Under 600 nm monitoring, a large charge transfer band from 250 to 340 nm composed of the electron transition of O2-–Sm3+ and O2-–W6+ and represented the strongest excitation at 300 nm. CLWO:Sm3+ emitted orange-red light at 600 nm (4G5/2–6H7/2) under the strongest excitation of 300 nm. The intensity ratio of the electric-dipole and magnetic-dipole of all the samples were bigger than 1. With the Sm3+-doped concentration increasing, the upward tendency of ratio values originated from the increased degree of lattice distortion. The calculated Rc (21.32 Å) and Q (3.78) represented the dipole–dipole interaction to account for the concentration quenching. With the temperature changing from 300 to 400 K, the chromaticity coordinates of samples just have a tiny difference (Δx = 1.02 × 10−4, Δy = 1.01 × 10−4). The thermal activation energy was calculated to be 0.42 eV and T0.5 > 480 K. The color purity of all the phosphors reached 98.9%. Ultimately, a white light-emitting diode (w-LED) was fabricated by coating trichromatic (red, blue, and green) phosphors on a near-ultraviolet chip. The fabricated w-LED revealed a high color rendering index (Ra = 91, R9 = 41) and a good chromaticity coordinate (0.320, 0.363) in the white area. Thus, these orange-red phosphors CLWO:Sm3+ with high thermal stability and high color purity can be potentially used in w-LED applications.