Broadband Near-Infrared Down-Shifting by Yb-O Charge-Transfer Band in Yb3+ Singly Doped Tellurite Glasses

Yb3+ singly doped tellurite as-prepared glasses and glass ceramics were synthesized by high-temperature melt-quenching method. The excitation and emission spectra have shown that there is an efficient near-infrared (NIR) down-shifting due to the sensitization of a novel Yb3+-O2- charge-transfer (CT) band. The CT band in the present host is located at around 320 nm at room temperature, which is much lower than that in other oxide hosts reported before. The possible energy-transfer mechanism from the Yb3+-O2- CT band to the F-2(5/2) multiplet of Yb3+ ions is discussed in detail. The concentration quenching is not observed even when the Yb3+-doped concentration is increased up to 40 mol%. The excitation of this strong broad CT band causes intense NIR emission of Yb3+:(F5/2F7/2)-F-2-F-2 from 920 to 1120 nm, making the tellurite glasses suitable for efficient photovoltaic (PV) application as a spectral conversion material for the crystalline Si (c-Si) solar cells.