Enhanced Quantum Efficiency via Co-Substitution in Red-Emitting Phosphor Sr2[MgAl5N7] : Eu2+ for Advanced Spectroscopic Applications Including Laser Displays with Ultra-High Luminescence Saturation Threshold.

Abstract

In order to obtain novel and more efficient red light-emitting materials, a series of Sr2[Mg1-xLixAl5-xSixN7] : 0.01Eu2+ (SMAN-xLS, 0≤x≤0.5) red phosphors were devised and successfully synthesized via the high temperature solid state reaction and the effects of the co-substitution of [Mg-Al]5+ by [Li-Si]5+ on structural and luminescence properties is investigated in detail. A series of powder XRD data and Rietveld refinement indicate that [Li-Si]5+ co-substitution can successfully enter the Sr2[MgAl5N7] : 0.01Eu2+ (SMAN) lattice. With the entry of [Li-Si]5+ into the lattice, the substitution of Al3+ by Si4+ leads to the weakening of the nephelauxetic effect of the 5d level of Eu2+, which shifts the emission peak from 657 nm to 647 nm and reduces the excitation in the green region, i.e., lowers the absorption of green light. When the amount of [Li-Si]5+ co-substitution is x=0.1, the luminescence intensity and thermal stability of the sample are enhanced, in which the external quantum efficiency (EQE), reflecting the luminescence intensity, is elevated by 49.6 %. The increase in lattice rigidity gives rise to higher luminescence intensity, and the introduced trap levels for the compensation of luminescence enhances the thermal stability. Under blue laser excitation, the SMAN-0.1LS can achieve an ultra-high luminescence saturation threshold of 52.22 W/mm2, which is remarkably superior to other existing red phosphors, a breakthrough performance that has enormous potential for application in high-power laser display light sources. Cathodoluminescence (CL) characterization and measurements attest to the favorable CL properties of SMAN-0.1LS. By measuring the pressure-dependent luminescence of SMAN-0.1LS, the emission peak can be shifted from 650 nm to 702 nm with the increase of pressure, and the sensitivity dλ/dP is 5.07 nm/GPa, which is indicative of the potential application of this system as an optical pressure sensor.