RESUMO
Cr3+ in the Ca3Sc2Si3O12 garnet (CSSG) has the ability to convert blue light to broadband near-infrared (NIR) emissions, which is a promising strategy for next-generation smart NIR light sources based on blue LEDs. The Cr3+ luminescence strongly depends on temperature due to electron-phonon coupling (EPC). We reveal the EPC mechanism of Cr3+ in CSSG for the first time by temperature-dependent photoluminescence measurement from 77 to 573 K and cathodoluminescence using a scanning electron microscope. Cr3+ occupies the Sc3+ site and experiences a weak crystal field in CSSG, manifesting a broad NIR emission in the 700-900 nm range that originates from the 4T2gâ4A2g transition. The zero phonon line (ZPL) of the 4T2 state is observed at â¼713 nm with a vibrational energy of â¼310 cm-1. A strong EPC leads to a large Stokes shift (â¼2900 cm-1). The Huang-Rhys parameter (S = 4), crystal field strength (Dq/B), and Racah parameters (B and C) are estimated.
RESUMO
Broadband near-infrared (NIR)-emitting phosphors are key for next-generation smart NIR light sources based on blue LEDs. To achieve excellent NIR phosphors, we propose a strategy of enhancing the crystallinity, modifying the micromorphology, and maintaining the valence state of Cr3+ in Ca3Sc2Si3O12 garnet (CSSG). By adding fluxes and sintering in a reducing atmosphere, the internal quantum efficiency (IQE) is greatly enhanced to 92.3%. The optimized CSSG:6%Cr3+ exhibits excellent thermal stability. At 150 °C, 97.4% of the NIR emission at room temperature can be maintained. The fabricated NIR-LED device emits a high optical power of 109.9 mW at 520 mA. The performances of both the achieved phosphor and the NIR-LED are almost the best results until now. The mechanism for the optimization is investigated. An application of the NIR-LED light source is demonstrated.