Luminescence properties of Tm₂O₃-doped germanate glass phosphors for near-infrared wideband light-source

Abstract

We synthesized Tm₂O₃-doped glass phosphors for a new near-infrared wideband light-source using a melt-quenching method and investigated their luminescence properties. Photoluminescence (PL) spectra at around 800 and 1200 nm were observed by blue light-emitting diode (LED) excitation in all samples. A shoulder structure appeared in the side of the short wavelength around 800 nm, and a dip structure around 1200 nm became deeper with increasing Tm₂O₃ concentration. The PL peak wavelength around 800 nm was shifted, and the PL intensity around 800 nm increased relative to that around 1200 nm with increasing Tm₂O₃ concentration. The PL band around 800 nm originated from the ¹G₄ → ³H₅ and ³H₄ → ³H₆ transitions, and the PL band around 1200 nm was attributed to the ³H₅ → ³H₆ transition, which was determined by PL and PL excitation measurements. The absorption and PL spectra suggested that the shoulder structure around 800 nm and the dip structure around 1200 nm were caused by the self-absorption phenomenon of Tm³⁺ ions. From the dependence of the PL spectra on the excitation wavelength and Tm₂O₃ concentration, we clarified that the PL peak shift around 800 nm and the change of the relative PL intensity ratio between the PL band around 800 nm and that around 1200 nm were due to the cross-relaxation phenomenon. We successfully achieved an ultra-wideband luminescence spectrum from 700 to 1300 nm that covers the "optical window in biological tissue" by co-doping the glass phosphor with Tm₂O₃ and PrF₃.