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

Abstract

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 ∼775 nm, with a full width at half maximum (FWHM) of ∼137 nm, an internal quantum efficiency (IQE) of ∼75%, and good thermal stability (I_423k ∼ 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 ∼80% 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 ∼18 mW at a drive current of 100 mA. These results indicate the great potential of CYHA:Cr³⁺ phosphor in NIR pc-LED applications.