High pressure narrowing of zero-phonon lines in polymer glasses at different temperatures

Spectral diffusion in polyethylene: Single-molecule studies performed between 30 mK and 1.8 K

“…This is consistent with spectral hole burning measurements that showed a decrease in the hole width and spectral diffusion with applied pressure. 21 We find that the ratios of the standard deviations of the distributions to the mean values for ␣ and ⌫ for both samples are ϳ20%. This might indicate that the physical origins of the distributions are related.…”

High-Resolution Laser Spectroscopy of Impurity Molecules in Organic Crystals and Polymers: Cryobaric Studies by Using Spectral Hole Burning Method.

“…1 lies in the fact that the holes burnt and scanned after pressure release at a low temperature are markedly narrower (3.4 GHz) than the holes in a non-pressurized sample (4.3 GHz). Note that the respective conditions (P =1 atm; T =4.2 K) were reached in the following It should be stressed that a theoretical consideration of the problem [15,17,26] has revealed a close relation of the observed effect, i.e. stronger pressure narrowing of spectral holes at higher temperatures, to the existence of the well-known peak (at about 3-5 K) in the specific heat C of many different glasses (in the plot of C/T3 versus T) and also to the presence of the low-temperature plateau in thermal conductivity of glasses.…”

“…We thank all coauthors in Tartu, Bayreuth and Ulm (see Refs. [8][9][10][11][12][13][14][15][16][17][18][19]) for fruitful collaboration. This work was partially supported by the Estonian Science Foundation, Grants No.…”

High-Pressure Studies of Optical Dephasing in Polymer Glasses

“…High pressure has recently been utilized as a theoretical − and experimental − probe of dynamics in glasses. These studies have revealed a variety of pressure-induced effects, including irreversible structural changes in covalent glasses, − narrowing of spectral holes in molecular glasses, , narrowing of spectral holes in polymer glasses above 4 K, ,, and dephasing in photon echo studies of polymeric glasses at low temperature. − These results have been interpreted in terms of irreversible collapse of the tunneling two-level system (TLS) in covalent glasses, − crystallization in a glass-forming liquid, collapse of the TLS in molecular glasses, the conversion of the TLS in strongly localized modes, , and a change in the form of the TLS density of states . The present study will investigate the effect of compression on TLS dynamics by utilizing the stochastic optical dephasing model of Geva and Skinner , to model pressure-dependent photon echo measurements of chromophores in polymeric glasses at variable low temperature.…”

“…At temperatures above 4 K, additional contributions to the line width can occur, and the interconversion of the TLS and strongly localized harmonic modes 48 has been proposed to explain the pressure-induced line narrowing of spectral holes reported for chlorine-doped polystyrene above 4 K. ,, The analysis of some pressure-dependent hole-burning studies of polymer glasses above 4 K 8,12 has assumed an empirical pressure-induced decrease in the line width; however, such an assumption is not valid at lower temperatures, where photon echo results show an opposite effect. − To avoid complications from high-frequency localized harmonic modes, the present study focuses on temperatures below 3 K where TLS interactions are dominant. Even the postulated pressure-induced conversion of the TLS into harmonic vibrational modes at higher temperatures was estimated to be less than a few percent up to 4 kbar; therefore, the present analysis of low-temperature photon echo results will initially assume the number of TLSs is unchanged.…”