The Urbach Tails and Reflection Spectra of NaCl Single Crystals

Takeo Miyata, Tetsuhiko Tomiki

In the tail part region of the first exciton band, the absorption constant (10-1 to 102 cm-1) was measured on zone-refined and Harshaw NaCl single crystals from 10°K to 573°K. Fundamental absorption tails of pure NaCl single crystals are represented by the modified Urbach rule, which describes the influence of zero-point lattice vibrations at low temperature. Analysing a temperature dependence of Urbach constant σ=σ0 F, it was found that σ0=0.757 and the temperature of zero-point phonon is ωℏ/2=58.2°K. Reflection spectra of single crystals were measured from 2112Å to 1060Å in the same temperature range. The peak shift of the first reflection band is investigated as a function of temperature to clarify the mode of phonons interacting with the exciton in the main part of the band. © 1967, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

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Materials
Curve 1
Temperature K: 10 Wavelength Range, µm: 0.108-0.212 Geometry θ θ' ω: 10° 10° Reported Error, %: ±3 Composition (weight percent), Specifications, and Remarks: Pure single crystal; purified by vacuum distillation followed by zone melting in chlorine using a quartz ampoule; cleaved; measured in vacuum (2 x 10⁻⁸ mm Hg); data extracted from smooth curve.
Curve 2
Temperature K: 78 Wavelength Range, µm: 0.109-0.212 Geometry θ θ' ω: 10° 10° Reported Error, %: ±3 Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 3
Temperature K: 195 Wavelength Range, µm: 0.110-0.212 Geometry θ θ' ω: 10° 10° Reported Error, %: ±3 Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 4
Temperature K: 298 Wavelength Range, µm: 0.105-0.212 Geometry θ θ' ω: 10° 10° Reported Error, %: ±3 Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 5
Temperature K: 473 Wavelength Range, µm: 0.110-0.212 Geometry θ θ' ω: 10° 10° Reported Error, %: ±3 Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 6
Temperature K: 573 Wavelength Range, µm: 0.109-0.212 Geometry θ θ' ω: 10° 10° Reported Error, %: ±3 Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.