We investigated a red to yellow color change observed in α-HgI₂ when cooled below 150 K. A phase transformation to β-HgI₂, which has a yellow color, was ruled out by a variable temperature x-ray diffraction study. Instead the color change at cryogenic temperatures is caused by a shift in the transmission edge to shorter wavelengths which we attribute to a widening band gap at low temperatures. Using optical transmission spectroscopy the width of the band gap was measured between 10 and 330 K. At room temperature the gap was 2.11 ± 0.03 eV which is significantly smaller than the most recently published values of ~ 2.3 eV. This smaller band gap was further verified by measuring the thermoelectric current at elevated temperatures.

Date Published: 10 January 2003
PDF: 6 pages
Proc. SPIE 4784, X-Ray and Gamma-Ray Detectors and Applications IV, (10 January 2003); doi: 10.1117/12.450820

Published in SPIE Proceedings Vol. 4784:
X-Ray and Gamma-Ray Detectors and Applications IV
Ralph B. James; Edwin M. Westbrook; Roger D. Durst; Larry A. Franks; Arnold Burger; Edwin M. Westbrook; Roger D. Durst, Editor(s)