A post-reduction strategy to enhance near-infrared-II emission from Li4SrCa(SiO4)2:Cr4+ phosphors

Abstract

Near-infrared-II (NIR-II) luminescence, which serves as a promising spectral window for biomedical applications and spectral analysis, has numerous potential applications. In this work, the NIR-II luminescence is realized in Li₄SrCa(SiO₄)₂:Cr⁴⁺ phosphors. Under 465 nm excitation, the emission peak of Li₄SrCa(SiO₄)₂:3%Cr⁴⁺ is located at 1215 nm and the full width at half maximum (FWHM) is more than 230 nm, covering the ultra-long range of 950–1600 nm. The photoluminescence spectra, diffuse reflectance spectra, Raman spectra and time-resolved emission spectra confirm the NIR-II luminescence mechanism. Furthermore, a novel post-reduction strategy is proposed to realize the leap-forward enhancement of NIR-II luminescence from Cr⁴⁺. By mutually substituting Sr²⁺ and Ca²⁺, a series of Li₄Sr_1+zCa_1−z(SiO₄)₂:3%Cr⁴⁺ (z = −1 to 1) samples are prepared to investigate the universality and applicable conditions of the post-reduction strategy. Benefitting from the NIR-II emission of Cr⁴⁺, it has great application potential in optical temperature measurement and spectral analysis.