High-pressure low-temperature phase transition in a doped<i>para</i>-terphenyl crystal: A spectral-hole-burning study

Abstract

The homogeneous width of zero-phonon lines in a chlorin-doped para-terphenyl crystal is determined by spectral hole burning at $T=4.2--14\mathrm{K}$ under various hydrostatic pressures up to 7 kbar. A drastic broadening of spectral holes with pressure occurs on approaching the order-disorder (triclinic-to-monoclinic) phase transition which takes place under $P\ensuremath{\approx}5.5\mathrm{kbar}$ at $4.2&lt;~T&lt;~14\mathrm{K}.$ The thermal broadening of spectral holes at fixed pressures is an activated process with the activation energy depending on pressure and having a deep minimum at $P\ensuremath{\approx}5.5\mathrm{kbar},$ i.e., in the phase-transition region.