Thermoluminescence of solutions in squalane after γ-irradiation

Abstract

The isothermal luminescence and thermoluminescence of squalane and its solutions has been studied following irradiation with y-rays at 77 K. The main solute used was biphenyl which gives excimer fluorescence under these conditions as well as monomer emissions. The luminescence is ascribed to ion recombination. It is only necessary to postulate two kinds of electron trapping, in the solvent or as solute anions, but there are five recombination processes giving glow peaks. If electron-attaching solutes are absent, the dominant process is thermal release of trapped electrons at -100K.In solutions of biphenyl most electrons form anions; these recombine with biphenyl cations when large molecules become mobile at the glass transition (-180 K). Close ion pairs can also decay by electron tunnelling : this produces the isothermal luminescence at 77 K. At intermediate temperatures, there is a peak ascribed to thermally assisted tunnelling ; this process becomes predominant at very high concentrations. Oxygen appears to act as a carrier of electrons between anions and cations, giving an extra peak, with a high proportion of phosphorescence, below the glasstransition. Carbon dioxide and sulphur hexafluoride also have striking effects on the glow-curves.Scavenging at 77 K can be distinguished from scavenging in the melting glass.

Quantum mechanical tunnelling in biological systems

“…Other pulse radiolysis data in the chemical field includes: Brocklehurst (1973), Brocklehurst, Bull & Evans (1975), Miller (1972Miller ( , 1973Miller ( , 1975, Miller & Willard (1972), Buxton & Kemsley (1976), Henglein (1974Henglein ( , 1975, Gratzel, Henglein & Janata (1975) and Frank et al (1976). Reviews have been written by Brocklehurst (1979), Hart & Anbar (1970), Rice & Pilling (1978), Hunt (1976), Kevan (1974), and a conference on 'Electrons in Fluids' (Proceedings, 1977).…”

Electron tunneling in molecular solids. An orbital overlap model

“…In general F\ = (foiA + /d'YaOx COS ( -0a) + (/dYa" -/d7a) sin X(0D -0A) (12) The functions f' and f" are listed in Table I. To describe the distribution of values of S2 it is convenient to define the reduced quantity V which ranges from 0 to 1 V = s2/smj = Noa(F0 + FJi + ...)2 (13) where is a normalization factor (Table II) and jx = Sx/S0; j «1 provided the intermolecular separation is large (below).…”

Thermoluminescent Charge Recombination in Saturated Hydrocarbons

“…The relationship between the thermoluminescence spectrum and electron trapping properties of the matrix has been extensively studied and analyzed in solid-state systems. − While thermoluminescence is an established technique for typical solid-state materials, it has been less frequently employed in studying organic crystals, , or glasses. − …”

“…The thermoluminescence studies that have been reported for nonpolar glasses 29-38 have established a number of interesting phenomena but have not particularly focused on the energetics of the process, albeit a few studies have utilized the initial rise method to determine activation energies of electron release in methanol glass 15 and anion release in 3-methylpentane ,,,, particularly the glass transition at which anion mobility becomes possible. Thermoluminescence spectra frequently supplement studies of isothermal recombination luminescence, − , and have facilitated observation of a number of novel emission processes 30,32,35,36 (cation−anion recombination, excimers, dimers, radicals, enhanced phosphorescence).…”

“…[22][23][24][25][26] While thermoluminescence is an established technique for typical solid-state materials, it has been less frequently employed in studying organic crystals, 27,28 or glasses. [29][30][31][32][33][34][35][36][37][38] The thermoluminescence studies that have been reported for nonpolar glasses [29][30][31][32][33][34][35][36][37][38] have established a number of interesting phenomena but have not particularly focused on the energetics of the process, albeit a few studies have utilized the initial rise method to determine activation energies of electron release in methanol glass 15 and anion release in 3-methylpentane. 29 Thermoluminescence peaks in glasses have been correlated with phase transitions, 27,30,33,37,38 particularly the glass transition at which anion mobility becomes possible.…”