Cr,Yb-codoped CaLaHfAlO garnet phosphor: electronic structure, broadband NIR emission and energy transfer properties.

The combination of a broadband near-infrared (NIR) phosphor and phosphor-converted light-emitting diodes (pc-LEDs) has proven to be an ideal choice for a high-efficiency NIR light source. Here, a garnet-type NIR CaLaHfAlO:Cr phosphor is obtained and its emission covered most of the NIR spectral range. Excited by 460 nm blue light, the maximum peak was located at 780 nm with a full width at half maximum (FWHM) of ∼141 nm and an internal quantum efficiency (IQE) of 33%. Moreover, the NIR spectra can be broadened by doping Yb into the CaLaHfAlO:Cr garnet phosphor. A super broad FWHM of 300 nm and reduced thermal quenching were acquired, originating from the energy transfer of Cr→ Yb. The energy transfer process of Cr and Yb is described by means of an energy level diagram and time-resolved spectrum. Finally, a NIR pc-LED is fabricated by combining the CaLaHfAlO:Cr,Yb phosphor with blue chips, which has a photoelectric conversion efficiency of 10%. These results demonstrate the great potential of CaLaHfAlO:Cr,Yb in super broadband NIR pc-LED applications.