Environment influence on the IR fluorescence of Xe₂* molecules in electron beam excited Ar--Xe mixture at high density

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We report new measurements of the near infrared (NIR) Xe₂* excimer fluorescence in an electron--beam--excited Ar (90%)--Xe (10 %) mixture at room temperature. Previous measurements up to a density N≈ 2× 10²⁶ m⁻³ discovered a broad excimer fluorescence band at ≈ 7800 cm⁻¹, whose center is red--shifted by increasing N (A. F. Borghesani, G. Bressi, G. Carugno, E. Conti, and D. Iannuzzi, J. Chem. Phys., 115, 6042 (2001)). The shift has been explained by assuming that the energy of the optical active electron in the molecule is shifted by the density--dependent Fermi shift and by accounting for the solvation effect due to the environment. We have extended the density range up to N≈ 6× 10²⁶ m⁻³, confirming the previous measurements and extending the validity of the interpretative model. A detailed analysis of the width of the fluorescence band gives a value of 2.85 nm for the size of the investigated excimer state. Such a large value lends credence to the validity of the proposed explanation of the experimental findings.