AN OPTICAL LINEWIDTH STUDY OF A CHROMOPROTEIN: C-PHYCOCYANIN IN A LOW TEMPERATURE GLASS

The temperature dependence of spectral holes burnt into a phycocyanin-doped ethylene glycol/water glass is investigated in the temperature range between 1.5 and 15 K. The data are well described by a power law with an exponent of 1.16 IO. 1. Chromopro-teins thus behave very much the same as glasses doped with small impurity molecules. The temperature dependence of the linewidth of optical holes is very sensitive to the structure and or-der of the lattice to which a photoreactive probe molecule is coupled. Whereas in crystalline materials this temperature dependence involves a high power of T or even an exponential, a rather low power law is characteristic for amorphous materials [ 11. For many systems a power law with an exponent of 1.3 has been observed [ 21. It should be stressed that the width of an optical hole may originate from several different processes such as direct electron-phonon scattering or phonon modulation of the electron