Jahn‐Teller Effect on Transition Metal Ions in Silver Halides III. Interpretation

Abstract

The temperature dependence of the optical absorptions involving orbital dublets (E,) split by dynamic Jahn-Teller effect (JTE) (measured on AgCl and AgBr doped with Ti3+, Fez+, and Crzf) is discussed. From the results obtained for excited E, states the linear JT-coupling parameters and the frequencies of the JT-active E, mode are derived. These E, modes are found to be localized around the impurity ion. It is shown that the small and temperature independent oscillator strength of the transition between the JT-splitting levels of the E, ground state (measured on Cr2+) is a consequence of the action of the dynamic JTE. The weak increase of the JT-splitting AE of the E, ground state with increasing temperature is caused by the temperature dependence of the frequency of the sg mode following from the thermal expansion of the crystal.Die Temperaturabhangigkeit der optischen Absorptionen zu und zwischen durch dynamischen Jahn-Teller-Effekt (JTE) aufgepaltenen Bahndublettzustanden E, (gemessen an AgCl und AgBr dotiert mit Ti3+. Fez+ und Cr2+) wird diskutiert. Fur den Fall angeregter E,-Zustande werden die linearen JT-Kopplungsparameter und die Frequenzen der JT-aktiven sg-Schwingungen bestimmt, die sich als lokalisierte Schwingungen erweisen. Es wird gezeigt, daB die kleine und temperaturunabhangige OszillatorenstLrke des ffbergangs zwischen den JT-Aufspaltungszustanden des Eg-Grundzustands (gemessen am CrZt) eine Folge des Wirkens des dynamischen JTE ist. Die in diesem Fall gemessene schwache VergroBerung der JT-Aufspaltung AE mit steigender Temperatur wird durch die Temperaturabhangigkeit der Frequenz der c,-Schwingung als Folge der thermischen Ausdehnung des Kristalls erklart.

Zeeman spectroscopy on Ti-doped GaAs and GaP

“…It should therefore be very weak in optical absorption, as found for the V3+ (d2) in GaAs (Ulrici et a1 1985). Furthermore, other, much broader, absorption peaks have already been identified with the Ti2+ charge state (Ulrici et a1 1986, 1987, Hennel et a1 1986. The intensity of these broad absorption peaks does not correlate with the intensity of the sharp line absorptions.…”

“…Note that the reduction of the spin-orbit splitting compared to the free-ion value in the excited state indicates a rather strong quenching of the orbital g-factor, which can be caused only by a Jahn-Teller coupling. From the quenching factor K = -0.13, a coupling strength of SE=EIT/ZIwE1: 1.4 can be derived from the relation IKl= exp(-S,) (Ulrici 1984).…”