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Non-Photochemical Hole Burning, NPHB, is one of a number of phenomena universally observed in glasses, and termed anomalous because they are not observed in crystalline solids. All of these phenomena are explainable by postulating the existence of a set of nearly isoenergetic configurations of the atoms or molecules of the glass. These configurations, first proposed independently by Anderson eta!.' and by Phillips2, are modelled as a double well potential and are called two level systems, 115. If there is a broad distribution of the parameters characterizing these potentials, all of the anomalous properties are explainable in terms of tunneling and phonon-assisted tunneling between the potential minima. NPHB is unique among these anomalous glass properties in that it requires the presence of a dilute probe species in the glass. For such systems, electronic or vibrational transitions of the probe are inhomogeneously broadened and monochromatic excitation, at w, of these transitions can cause a loss of absorption at the excitation frequency. This is the hole burning phenomenon. The presence of the probe molecule can cause some TLS strongly coupled to the probe to differ from their intrinsic properties. Thus these TLS have been called TLSCx to indicate their interaction with the extrinsic probe species. The other TLS are refered to as TLSmt, with the subscript indicating their intrinsic nature. In a model of NPHB proposed by Small and Shu4, it is the rate of conversion of ThS that is the rate determining step for hole formation. For short bum times, however, the hole widths are determined by ThS. Thus NPHB can be used to probe both short range (TLS) and spatiallyaveraged (TLS) glass properties. In this paper, we report on the use of NPHB (kinetics and hole widths) to investigate structural details of various materials. We first present data on NPHB of the dye oxazine 720 in two different forms of glassy ethanol. Next, we show how NPHB is sensitive to the configurational relaxation that occurs in glassy water at temperatures between 100 K and the glass to crystal transition temperature. Finally, we present some preliminary data on NPHB of the DNA binding dye, TO-PRO-3.
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