. . . "terial allowing transmittance of light ranging from the red to far-infrared wavelength, the inventors found: that a transition metal element, such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Rh or Ru, has an ion radius close to that of Ga or In, and thus the Group III-V non-nitride can be adequately formed as a single crystal even if about 25 at % of Ga or In in the Group III-V non-nitride is substituted wi" .