GE's transparent Yttralox was followed by GTE's lanthana-doped yttria with similar level of additive. Both of these materials required extended firing times at temperatures above 2000 °C. La2O3 – doped Y2O3 is of interest for infrared (IR) applications because it is one of the longest wavelength transmitting oxides. It is refractory with a melting point of 2430 °C and has a moderate coefficient of thermal expansion coefficient. The thermal shock and erosion resistance is considered to be intermediate among the oxides, but outstanding compared to non-oxide IR transmitting materials. A major consideration is the low emissivity of yttria, which limits background radiation upon heating. It is also known that the phonon edge gradually moves to shorter wavelengths as a material is heated.