Enhancing and tuning broadband near-infrared (NIR) photoluminescence properties in Cr3+-doped Ca2YHf2Al3O12 garnet phosphors via Ce3+/Yb3+-codoping for LED applications

A near-infrared emitting phosphor-converted light-emitting diode (NIR pc-LED) attracts much attention for its promising applications in night vision, biosensors, food composition and freshness measurement areas and so on, while the discovery of broadband NIR phosphors remains a challenge. Herein, an efficient broadband NIR-emitting Ca2YHf2Al3O12:Cr3+ (CYHA:Cr3+) garnet phosphor is successfully developed. Under 460 nm light excitation, the developed Ca2YHf2Al3O12:Cr3+ (CYHA:Cr3+) shows broadband NIR emission from 650 to 1000 nm peaking at similar to 775 nm, with a full width at half maximum (FWHM) of similar to 137 nm, an internal quantum efficiency (IQE) of similar to 75%, and good thermal stability (I-423k similar to 80%). To further improve and tune the photoluminescence (PL) properties of Cr3+-activated CYHA, a strategy of energy transfers (ETs) is designed in CYHA. Through the ET of Ce3+ -> Cr3+, the absorption of Cr3+ can be effectively enhanced. Utilizing the Cr3+ -> Yb3+ ET, the spectral intensity of Yb3+ is obviously strengthened and the NIR emission bandwidth is broadened. In addition, Yb3+-codoping improves the thermal stability from similar to 80% to similar to 90% at 423 K, principally originating from the efficient ET from Cr3+ to more thermally stable Yb3+ emitters. Here, ETs of Ce3+ -> Cr3+, Ce3+ -> Yb3+, Cr3+ -> Yb3+, and Ce3+ -> Cr3+ -> Yb3+ in CYHA are systematically analyzed based on PL lifetime and ET mechanisms are proposed. Finally, as-fabricated NIR pc-LED combining CYHA:Cr3+,Yb3+ with a blue LED chip, gives a maximum NIR output power of similar to 18 mW at a drive current of 100 mA. These results indicate the great potential of CYHA:Cr3+ phosphor in NIR pc-LED applications.