Journal of Physical Studies 2(3), 409–420 (1998) DOI: https://doi.org/10.30970/jps.02.409 THE MULTIMODE JAHN–TELLER EFFECT IN ONE–PHONON SIDE–BAND OF OPTICAL ABSORPTION SPECTRUM Γ8(4A2e4t3) → Γ8(ψ)(4T1e3t4) OF THE CdTe:Co2+ SYSTEM

V. Z. Polinger¹, Yu. P. Gnatenko¹, P. N. Bukivsky¹,S. V. Melnichuk², I. M. Yurijchuk^2
1Institute of Physics, Nat. Ac. Sci. Ukraine, 46 Nauky Pr., Kiev–28, UA–252028, Ukraine
²Chernivtsi State University, 2 Kotsiubynskyi Str., Chernivtsi, UA–274012, Ukraine

Complicated fine structure in the low–temperature optical absorption band of the impurity $d → d$ transition $Γ_{8}({}^{4}A_{2} e^{4}t^{3})→Γ_{8}^{(ψ)} ({}^{4}T_{1} e^{3}t^{4}) $ for semiconductor crystal CdTe doped by impurity Co$^{2+}$ ions substituting tetrahedral Cd sites was studied experimentally and interpreted theoretically in terms of multimode Jahn–Teller effect for the excited term $Γ_{8}^{(ψ)} ({}^{4}T_{1} e^{3}t^{4})$ coupled to trigonal and tetragonal modes. An attempt to use the old classical theory of impurity absorption ignoring the Jahn–Teller effect and treating the optical band in terms of phonon replicas turned out to fail. The one phonon side–band of the optical band in question has nothing in common with the projected phonon densities calculated for the defect crystal using the RIM–11 model. The multimode Jahn–Teller effect $Γ_{8}\bigotimes(e+t_{2})$ considered in terms of second–order perturbation theory resulted in a considerable redistribution of the projected densities of states and in appearance of new resonant vibronic modes. The experimental spectral line in the region of one–phonon side–band fitted well with the theoretical curve obtained by the adjustment of vibronic constants.

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