Normal spectral emissivities of liquid Ag-Cu alloys in the visible and infrared regions

The wavelength and composition dependencies of normal spectral emissivities for liquid Ag-Cu alloys have been measured over a wavelength range between 450 and 1500 nm at temperatures from 1273 to 1423 K in a cold crucible furnace. The spectral emissivities abruptly increase in the visible region with decreasing wavelength. The wavelength at the abrupt increase in the emissivity shifts to a shorter wavelength as the concentration of silver in the alloy increases. This suggests that the abrupt increases are attributed to the direct interband transition, and the energy gap between the d band and the Fermi level increases with an increase in silver concentration in the alloy. To the contrary, the spectral emissivities in the infrared region were found to exhibit weak negative wavelength dependencies, which are attributed to the intraband transition. The composition dependencies of spectral emissivities observed in the infrared region have been explained by the Drude model.