Near-infrared engineering for broad-band wavelength-tunable in biological window of NIR-Ⅱ and -Ⅲ: A solid solution phosphor of Sr1-xCaxTiO3:Ni2+

Abstract

In this study, near-infrared (NIR)-emitting Sr1-xCaxTiO3:0.01Ni2+ (x = 0, 0.25, 0.5, 0.75, 1) solid-solution phosphors were prepared by a high-temperature solid-state reaction method. The effect of Ni2+-doping phase transformation on the crystallographic, luminescence properties, and electron density performance of Sr1-xCaxTiO3:1%Ni2+ phosphors are investigated. Upon 350 nm excitation, the phosphors could produce broadband NIR light within the biological windows of NIR-Ⅱ and -Ⅲ, originating from the 3T2g(F) → 3A2g(F) spin-allowed electron transition of Ni2+ in the octahedron, in full-width half-maximum spectra of over 200 nm. Through the Rietveld refinement analysis and density functional theory calculations, the results show that the NiO6 octahedron is twisted and distorted, reducing the crystal field strength and effective coordination around Ni2+ ions are the main reason for the emission peaks of SrTiO3:Ni2+ shift from 1311 to 1377 nm by substituting Ca2+ under excitation by UV light at 350 nm. In addition, SrTiO3:Ni2+ has an internal quantum yield of up to 6.5%. All these results indicate that Sr1-xCaxTiO3:Ni2+ phosphors have potential applications as a source for NIR lighting.