Photoluminescence properties of a ScBO₃:Cr³⁺ phosphor and its applications for broadband near-infrared LEDs

Abstract

The rapid extension of solid state lighting technologies offers the possibility to develop broadband near-infrared (NIR) phosphor-converted LEDs (pc-LEDs) as novel NIR light sources. In this paper, a new NIR-emitting phosphor ScBO₃:Cr³⁺ was synthesized by a high temperature solid state reaction method. Phase structure, spectroscopic properties, luminescent lifetime, quantum yield, emitter concentration influences and thermal quenching behavior of ScBO₃:Cr³⁺, as well as its applications for NIR pc-LEDs, were systematically investigated. ScBO₃:Cr³⁺ phosphors exhibit a broad absorption band ranging from 400 to 530 nm, which matches well with the characteristic emission of the blue LED chip. Moreover, Cr³⁺ ions occupy the Sc³⁺ sites with relatively low crystal field strength in the ScBO₃ host, and therefore ScBO₃:Cr³⁺ phosphors show intense broadband emission peaking at ∼800 nm upon excitation at 460 nm, originating from spin-allowed ⁴T₂ → ⁴A₂ transition of Cr³⁺ ions. The optimum Cr³⁺ concentration was determined to be ∼2 mol% with a quantum yield of ∼65%. A broadband NIR pc-LED prototype device was fabricated by the combination of ScBO₃:Cr³⁺ phosphors and a blue LED chip, which showed a maximum NIR light output power of ∼26 mW and a corresponding energy conversion efficiency of ∼7%. The results indicate the great potential of ScBO₃:Cr³⁺ phosphors for applications in broadband NIR pc-LEDs.