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The absorption spectra of KZnF3:Tl+ and KMgF3:Tl+ crystals have been measured over the energy range 1.5-6.4 eV at temperatures of 10-300 K. A wide absorption band with a clear doublet structure identified as an absorption A band of Tl+ impurity centres is observed for both crystals. The position of the band, its bandwidth and the distribution of absorption intensity between the two components of the band are temperature dependent in the range T>65 K. All features of the absorption spectra of the crystals studied are explained within the frameworks of the conventional theory on the basis of the Frank-Condon principle and the semiclassical picture of crystal lattice vibrations. The band shapes calculated by the Monte Carlo method are in satisfactory agreement with observed ones.

Raman processes of spin-lattice relaxation. The spin-lattice relaxation rate anomaly revealed near T C in the superconducting species can be assigned to the phonon density spectrum changes.

The luminescence spectra of KZnF3:Tl+ and KMgF3:Tl+ crystals with a perovskite structure were investigated in the temperature range of 4.2–300 K and at optical excitation in the A absorption band (∼6 eV). The spectrum of KZnF3:Tl+ at 300 K is a wide band with the maximum Emax at 5.48 eV and the width of about 0.47 eV. At 100 K the band splits into two components: an intensive one with Emax = 5.63 eV and a width of about 0.2 eV and a weak one with Emax = 4.66 eV. At 4.2 K an intensive broad band practically disappears and a narrow line accompanied by a vibration structure is observed at E = 5.725 eV. This line is assigned to a zero-phonon transition from the metastable 3 Γ 1u level to the ground 1 Γ 1g level, weakly allowed due to the hyperfine interaction and phonon-assisted mechanisms. The spectrum of KMgF3:Tl+ at 300 K is a band with the maximum at 5.78 eV and a width of about 0.3 eV. This band does not disappear at 4.2 K; its maximum shifts to higher frequencies (5.91 eV) and an intensive narrow line at 5.812 eV is observed on its background. The temperature-dependent luminescence decay was also investigated. At T = 10 K the lifetime of the slow component of luminescence is τs = 11.6 ms for KZnF3:Tl+ and τs = 14.9 ms for KMgF3:Tl+. The main features of the observed luminescence spectra are satisfactorily explained within the framework of the conventional theory, as a manifestation of the Jahn–Teller effect for the excited 6sp electron configuration of an admixture Tl+ ion, with a set of model parameters close to that used earlier to describe absorption spectra of the studied crystals.

The electron spin±lattice relaxation (SLR) times T 1 of Yb 3 ions were measured from the temperature dependence of electron spin resonance line width in Y 0X99 Yb 0X01 Ba 2 Cu 3 O x with dierent oxygen contents. Raman relaxation processes dominate the electron SLR. Derived from the temperature dependence of the SLR rate, the Debye temperature (H D ) increases with the critical temperature T c and oxygen content x. This relationship between T c and H D can be well understood in terms of the modi®ed Bardeen±Cooper±Schriefer theory of phonon mechanism for a strong electron± phonon coupling. Ó