Achieving the potential multifunctional near-infrared materials Ca3In2−xGaxGe3O12:Cr3+ using a solid state method

Abstract

Near-infrared spectroscopy is developing rapidly in the fields of human detection and food analysis due to its fast response and non-invasive characteristics. Herein, we report the novel near-infrared garnet-type Ca₃In₂Ge₃O₁₂:xCr³⁺ and Ca₃In_2−xGa_xGe₃O₁₂:0.07Cr³⁺ phosphors, in which there are two crystallographic sites (CaO₈, InO₆) that can be substituted by Cr³⁺, and cation regulation engineering for In³⁺ is utilized to tune the luminescence properties. Under the 480 nm excitation, the Ca₃In₂Ge₃O₁₂:xCr³⁺ phosphor emits a broad spectrum at 650–1150 nm, which matches well with the first biological window. The concentration quenching mechanism and luminescence mechanism of Ca₃In₂Ge₃O₁₂:xCr³⁺ were studied and the site assignment of the two luminescence centers was discussed using low temperature spectra and fluorescence decay curves. The application performance of the phosphor was improved by introducing Ga³⁺ to substitute for In³⁺, and the blue shift of nearly 50 nm was explained by crystal field and nephelauxetic effects. At the same time, a 24% increase in the activation energy of thermal quenching of phosphors was obtained, which has been analyzed using the mechanism of phonon transition and the change of structural rigidity. Thus, the near-infrared emitting Ca₃In_0.2Ga_1.8Ge₃O₁₂:0.07Cr³⁺ phosphor was obtained, which has lower cost, higher emission intensity, and much better thermal stability, spreading the application of phosphors in plant far red light illumination, human body detection, and spectral conversion technology of silicon-based solar cells. Simultaneously, an example of a near-infrared plant illumination experiment is given, demonstrating that a cation substitution strategy based on crystal field control could be applied to tune spectral distribution and develop novel potential phosphors for practical optical application.