Rare-earth oxides such as ytterbium oxide (Yb 2 O 3) and erbium oxide (Er 2 O 3) are the most commonly used selective emitters. These oxides emit a narrow band of wavelengths in the near-infrared region, allowing the emission spectra to be tailored to better fit the absorbance characteristics of a particular PV material. The peak of the emission spectrum occurs at 1.29 eV for Yb 2 O 3 and 0.827 eV for Er 2 O 3. As a result, Yb 2 O 3 can be used a selective emitter for silicon cells and Er 2 O 3, for GaSb or InGaAs. However, the slight mismatch between the emission peaks and band gap of the absorber costs significant efficiency. Selective emission only becomes significant at 1100 °C and increases with temperature. Below 1700 °C, selective emission of rare-earth oxides is fairly low, further decreasing efficiency. Currently, 13% efficiency has been achieved with Yb 2 O 3 and silicon PV cells. In general selective emitters have had limited success. More often filters are used with black body emitters to pass wavelengths matched to the bandgap of the PV and reflect mismatched wavelengths back to the emitter.