Highly efficient and thermally stable broadband near-infrared emitting garnet Ca3Sc2Ge3O12:Cr3+,Ce3+ phosphors for multiple pc-LED applications

Abstract

With the increasing demand for the application of near-infrared (NIR) spectroscopy in security, agriculture, medical and other fields, people have been seeking efficient and intelligent NIR light sources. Herein, Cr³⁺ doped Ca₃Sc₂Ge₃O₁₂ (CSGG) broadband NIR phosphors are successfully synthesized. Under excitation of 480 nm, the emission peak of CSGG:Cr³⁺ is located at 785 nm, and the full width at half maximum (FWHM) is 106 nm. Low photoluminescence spectra (7 K and 77 K) support the broadband NIR emission coming from two Cr³⁺ luminescence centers occupying ScO₆ and CaO₈ sites, respectively. CSGG:Cr³⁺ exhibits excellent thermal stability (97% at 100 °C) and low internal quantum efficiency (IQE = 22%). The introduction of Ce³⁺ leads to the enhancement of IQE from 22% to 61% due to the following two reasons: the energy transfer from Ce³⁺ to Cr³⁺ and the lattice distortion which improves the parity forbidden transition of Cr³⁺. The mechanism of excellent luminescence thermal stability is revealed from the following perspectives: thermal activation energy, the Huang–Rhys factor and the thermal ionization effect. Benefiting from the excellent performance of CSGG:Cr³⁺,Ce³⁺ NIR phosphors, the combination with blue light chips demonstrates their potential applications in night vision security, biological imaging, and nondestructive testing.