Near-Infrared Phosphor Zn₂InGaO₅:Cr³⁺ with a Wide Bandgap Applicable for Light Sources at Low Temperature

Differing from traditional near-infrared (NIR) light sources that are made from thermal radiation of a blackbody or filtered light from gas discharge, the technique by converting blue emission of light-emitting diode (LED) chips into NIR light provides a solution. For this purpose, the NIR phosphor should be developed at first. In this work, we report a phosphor Zn2InGaO5:Cr3+, synthesized at 1450 °C for 5 h in air ambient, applicable for NIR LED light sources for application at low temperature no higher than 200 K. The Zn2In0.98Cr0.02GaO5 phosphor and the Zn2InGaO5 host have a direct band gap of about 3.00 and 3.03 eV, respectively, and belong to the class of bandgap semiconductors. Excited by 471 nm at room temperature, the phosphor gives ultrabroadband emission, peaked at 826 nm with a full width at half-maximum (FWHM) of 192 nm, in the region of 700–1100 nm. The luminescence intensity increases as the temperature increases from 10 to 200 K, maximizes at 200 K, and then decreases as the temperature increases further, showing an anomalous temperature-quenching effect. Meanwhile, the emission peak blue-shifts continuously from 826 to 779 nm. The output power of the NIR pc-LED device packaged using the Zn2InGaO5:Cr3+ phosphor driven under the current of 100 mA at room temperature is 5.14 mW, for which the photoelectric conversion efficiency is 1.9%.