Temperature shift of the Fe²⁺ absorption band in LiNbO₃:Fe crystal

Abstract

The temperature dependence of the Fe 2+ absorption band of a strongly oxidized LiNbO 3 : Fe crystal is reported over the range from 25 to 350 °C, where the effect of temperature on the band is reversible. The band broadens and shifts to lower energy as temperature is increased. The rate at which the absorption peak energy decreases with increasing temperature is calculated as -6.8 × 10-5 eV/°C from the slope of the straight-line fit to the temperature against peak position energy graph. We propose that the origin of the temperature shift is due to both a shift of the energetic position of impurities and the decrease of the band gap energy. The consistency between the calculated rate by the help of a simplified model which describes the shift of the band gap energy in the frame of the lattice dilation and the observed rate suggests that the lattice dilation might be responsible for the temperature shift of the band.

Optical properties of iron-doped lithium niobate crystal depending on iron content and temperature

“…We have previously reported high temperature shift of Fe 2þ absorption band over the range from 298 to 623 K as À6.8 Â 10 À5 eV K À1 for a 0.03 mol% iron doped LiNbO 3 crystal. Present value agrees with our previous high temperature result [19]. This agreement between two crystals of diferent iron contents indicates that other contents of Fe would display a similar behavior.…”

In situinvestigation of optical absorption changes in LiNbO3during reducing/oxidizing high-temperature treatments

“…That means that the changes that take place directly during the cooling process escape observation. We know of only two publications [23,24], where in situ investigations of optical absorption were carried out for Fe-doped LN crystals in the spectral region of absorption of the Fe ions, however in a narrow temperature range.…”