Electrical and Optical Properties of Rutile Single Crystals

Clear, synthetic rutile (Ti${\mathrm{O}}_2$) single crystals have been investigated by electrical and optical methods. It seems possible to correlate the high temperature conductivity ($E_G=3.05\mathrm{}$ ev) with the threshold of optical absorption at low temperatures (3.03 ev) and with the maximum of the photoconductivity (3.03-3.06 ev). This evidence indicates an energy gap $\mathrm{ca} 3.05$ ev for rutile as an insulator.