A high quantum efficiency plant growth LED by using a deep-red-emitting α-Al₂O₃:Cr³⁺ phosphor

Although it has been extensively studied for decades, the α-Al₂O₃:Cr³⁺ phosphor has rarely been investigated for horticultural lighting. In this work, for the first time, a prototype of a plant growth light-emitting diode (LED) has been fabricated by coating a deep-red-emitting α-Al₂O₃:Cr³⁺ phosphor onto a near-ultraviolet (NUV) chip. The α-Al₂O₃:Cr³⁺ phosphor, synthesized by a co-precipitation method and annealed at 1500 °C for 2 h, emits an outstanding narrow peak at 695 nm. The α-Al₂O₃:0.6%Cr³⁺ phosphor shows a high activation energy of 0.29 eV, a long lifetime of 3.4 ms, and a superior color purity of 100%. The chromatic coordinates and the QE value of the red LED obtained by coating an α-Al₂O₃:0.6%Cr³⁺ phosphor on a NUV chip are (x = 0.5650, y = 0.2429) and 87.1%, respectively.