Transmission spectra of crystals at elevated temperatures for the calculation of internal radiant heat transport during crystal growth – Part 2: Spectra of YAG:Cr, YVO₄:Nd and the bandgap variation of various materials

Abstract

The transmission spectra in the range from 350 to 3500 nm of the two most complex materials with regard to radiant heat transport -YAG:Cr +4 and YVO 4 :Nd -are reported for temperatures between 25 and 1310°C. The extreme shift of the short wavelength cut-off (band gap) of YVO 4 :Nd with temperature is shown in comparison to that of some other materials. In YAG:Cr 4+ we found a light-induced absorption band near 2000 nm besides a strong reduction of the transmission in the visible and the near IR with increasing temperature.

Transient and near‐edge absorption in YVO4 crystals

“…According to [7] the YVO crystals grown in N 2 +1%O 2 atmosphere turn colourless when they are annealed at high temperature (above 1000 °C) in air, N 2 , Ar+O or O 2 atmospheres. The opposite effects were earlier reported in [8] for YVO 4 :Nd crystals grown in Ar+0.5%O 2 atmosphere: in the visible region, a strong irreversible reduction of the transmission was observed after heating in air. Thereby, the decoloration mechanism and the origin of colour centers are complicated and have not been clear until now.…”

Spiral formation during Czochralski growth of rare-earth scandates

“…This was proven by Polity et al [39], who measured the change of the transmission spectra of Cr 4+ :YAG in the 350-3500 nm range at temperature between 25 and 1310 1C. They found a continuous increase of the absorption with rising temperature in the 700-1000 nm and 1100-1700 nm ranges.…”