Highly efficient and thermally stable Cr3+-activated silicate phosphors for broadband near-infrared LED applications

A novel broadband near-infrared (NIR) phosphor LiInSi2O6:Cr3+ (LIS:Cr3+) is successfully synthesized via solid-state reaction. Its crystal structure, photoluminescence properties as well as the application in NIR phosphor-converted LEDs (pc-LEDs) are explored. The LIS:Cr3+ phosphor has two absorptions bands centered at ~460 and 670 nm, respectively. Under 460 nm excitation, it shows the broadband NIR emission peaking at ~840 nm with a full width at half maximum (FWHM) of ~143 nm. The optimum Cr3+ concentration is found to be ~6 mol%, whereas the intensity decrease at further increased Cr3+ content is attributed to the radiative energy transfer process. The LIS:0.06Cr3+ phosphor has a quantum yield of ~75% and can retain ~77% of the initial intensity at 150 °C. Highly efficient, thermally stable and broad NIR emissions of LIS:Cr3+ phosphors are caused by the Cr3+ preferential occupancy in [InO6] octahedron with weak crystal field but relatively strong rigidity. The NIR pc-LED is fabricated by combining the LIS:Cr3+ phosphor with the blue LED chip, which has the NIR output power of ~51.6 mW and the photoelectric efficiency of ~17.8% at 100 mA drive current. The results suggest that LIS:Cr3+ phosphors have great potential for applications in broadband NIR pc-LEDs.