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Matrix interactions with rare‐gas oxide excimers

Abstract: Matrix interactions of rare‐gas oxide molecules formed in solid matrices were studied by photoluminescence.Excitation energies between 8–12 eV were provided by both synchrotron radiation at the Stanford Synchrotron Radiation Laboratroy (SSRL) and a hydrogen discharge source at UCSB. Photoluminescence emission and excitation spectra of Ar:CO2(1%), Kr:CO2(1%), Kr:N2O(1%), and Kr:O2(1%) mixtures were obtained. Radiative lifetimes of ArO and KrO emissions from CO2doped Ar and Kr matrices were also measured. The direct photodissociative threshold of CO2 to CO(X 1S+)+O(1 S) in an Ar matrix was found to be 10.6 eV, in agreement with that of the gas phase. Further unambiguous evidence for radiationless, dissociative energy transfer, between the matrix free exciton and CO2, probably by a harpooning mechanism, was seen in Kr:CO2 below the direct photodissociation threshold. Temperature, matrix annealing, and character of the photofragment were found to have significant effects on the rare‐gas oxide molecular binding and production rate.

R. V. Taylor, W. Scott, P. R. Findley, Zenglie Wu, W. C. Walker and K. M. Monahan

Energy transfer in solid Xe and Kr doped with N2O

Abstract: Photoluminescence excitation, emission, and decay spectra were obtained for solid Xe:N2O and Kr:N2O mixtures using vacuum ultraviolet synchrotron radiation as the excitation source. The principal emitting species were determined to be XeO(1 D) and KrO(1 S) excimers. Fluorescence decay measurements indicate that the XeO(1 D) emission arises from two excited states.Analysis of the emission and excitation spectra leads to the conclusion that XeO(1 D) production follows nonradiative energy transfer to N2O from self‐trapped excitons in the xenon host.

K. M. Monahan and V. Rehn

Photodissociative production of O(1 S) from N2O and S(1 S) from OCS in rare gas matrices

Abstract: Photoluminescence excitation spectra of Ar:N2O (1%), Ar:OCS (1%), and Kr:OCS (1%) were obtained in the region 180–104 nm, using UVsynchrotron radiation at SSRL. Photodissociationenergy thresholds in the matrix were found to be: 8.06 eV for N2O→N2(X 1Σ+)+0(1 S) and 7.17 eV for OCS→CO (X 1Σ+)+S(1 S). Our results show several effects due to interactions between the matrix and the triatomic molecule: (1) differential blue shifts of the 1Π←1Σ+ and 1Σ+←1Σ+ transitions, (2) a greatly enhanced predissociation rate from 1Π to 1Σ+, (3) matrix dependent energy shifts of a particular Rydberg state, (4) nonradiative energy transfer between the matrix and the triatomic, involving either self‐trapped excitons and a Foster–Dexter mechanism or free excitons and a harpooning mechanism. To our knowledge, this is the first observation of the free exciton–harpooning mechanism in a rare gas matrix.

R. V. Taylor, W. C. Walker, K. M. Monahan and V. Rehn

Optical properties of the (CuInSe2)1−x−(2ZnSe)x system

Abstract: Optical electronic transitions were studied in the (CuInSe2)1−x−(2ZnSe)x system from 0.5 to 14 eV. The system crystallizes in the chalcopyrite structure for x≤0.43 and in the zinc-blende structure for x≥0.48. The absorption edge was found to be direct for all the compositions and the energy gap varies with x parabolically, without discontinuity at the structural transition. This dependence is associated with the substitutional disorder in the mixtures. Reflection measurements showed substantial differences between the compositions with the chalcopyrite structure and those with the zinc-blende structure. The additional peaks observed for the compounds with the chalcopyrite structure are ascribed to pseudodirect transitions which become allowed by zone folding. The optical constants in the visible and ultraviolet regions were determined from the reflection spectra by Kramers-Kronig analysis. The dependence of the absorption bands on composition and structure is discussed and possible assignments are suggested. The effective number of electrons per atom contributing, in the energy range studied, to optical transitions was calculated and was found to depend strongly on the amount of Cu d electrons in the mixture as well as on the crystal structure.

J. N. Gan, J. Tauc, V. G. Lambrecht, Jr., and M. Robbins