Broadband near-infrared luminescence of impurity Fe3+ in borate glass: A promising material for glass-converted light-emitting diodes

A novel strategy for effectively enhancing the near-infrared (NIR) broadband luminescence of Fe 3+ by modifying the symmetry of the Fe 3+ coordination field is developed and evaluated. The borate glass doped with F (fluorine) or S (sulfur) prepared in a reducing atmosphere exhibits broadband NIR luminescence in the 500–1150 nm wavelength range under approximately 360 nm near-ultraviolet (NUV) excitation. The emission peak wavelength is about 740 nm, with a full-width at half maximum (FWHM) of 225 nm and an average lifetime of several hundred microseconds. Combining photoluminescence (PL), absorption (Abs), and electron paramagnetic resonance (EPR) spectroscopy, we proposed that this NIR emission originates from the tetrahedral impurity Fe 3+ coordinated with F − or S 2− in the glass. The presence of F and S alters the symmetry of the local coordination of Fe 3+ centers, resulting in increased splitting of the d-electrons, hence, enhancing the luminescence of the d→d transition. In addition, an NIR gc-LED device is developed by coupling NIR fluorescent glass with a 365 nm commercial near-ultraviolet light-emitting diode (LED). This NIR gc-LED device can be utilized for nondestructive internal detection, nondestructive imaging of blood vessels in the human finger, and night vision. The transparent glass developed in this work is an excellent addition to the group of novel NIR materials and displays significant potential for NIR luminescence applications.