Anomalous decay of the slow emission component in certain doped alkali halides was explained by the creation of a discrete breather in the immediate neighborhood of the impurity. It was experimentally observed that with rising temperature the decay anomaly becomes less pronounced, finally disappearing in the range 100 K to150 K (depending on the substance). In view of the breather explanation, this temperature dependence should be a consequence of the effect of temperature on breathers. We present an improved model of the dissipative effects of temperature on lattice breathers so as to compare it to the observed experimental temperature behavior.
Introduction Luminescence of various alkali halides doped by heavy ns2 ions excited in the Aabsorption band displays an anomaly in the decay of the slow component [1,2]. The initial part of the decay, up to several milliseconds, is nonexponential. This anomaly was explained by assuming extremely slow relaxation of the crystal lattice as a response to the Jahn-Teller effect acting on the emission center in its excited state [3]. The slowness of the lattice relaxation was later ascribed to the creation of a discrete breather in the immediate neighborhood of the impurity [4]. As experimentally observed, the anomaly is most pronounced at the lowest temperatures. As the temperature increases the anomaly weakens and is finally extinguished around 100-150 K, depending on the lattice substance. In view of the breather explanation the temperature dependence of the anomaly should be the consequence of temperature effects on the breather. Such effects are under investigation; however, so far they are still not fully understood. Thermal relaxation of the breather in a monatomic nonlinear chain shows [5][6][7] that breathers are likely to be spontaneously created if the initial temperature is sufficiently high. Thermal background can also set the breather in motion [7,8] and cause the breather to collide with other excitations and chain boundaries. Stability of the breather in thermal equilibrium for one and two-dimensional monatomic lattices is studied in [9,10].In the case of the decay anomaly due to breather creation, experimental data on the anomaly's temperature dependence suggest that increasing temperature causes the breather to decay, ultimately leading to its destruction, together with the disappearance of the decay anomaly. We now provide a model of finite temperature effects on the decay of the breather in a diatomic non-linear chain. The model confirms the expected tendency consistent with experimental data on the decay anomaly: the higher the temperature, the faster the decay of the breather.