强磁场下顺磁掺杂离子的光谱扩散

采用一种简明的解析方法从纯粹频域的角度讨论强磁场下顺磁离子掺杂体系的光谱扩散过程。一般说来光谱扩散遵循[1-exp(-WT_w)]^x的形式,W是跳变速率,T_w为等待时间。在不存在冷冻核时,对于频域和时域x分别为1/2和1。考虑到冷冻核效应,光谱扩散的速率将近似地以因子(ω_eff/ω₀)²减慢,这里ω₀是描述冷冻核的特征频率。当冷冻核充分大时,频域和时域的光谱扩散的行为趋于一致x≈0.22。

Spectral Diffusion of Doped Paramagnetic Ions at High Mag netic Field

Random frequency modulations exist in many systems, such as magnetic system and glasses at low temperature, dye-solution. In magnetic systems, spin flips of doped ions or nuclei in the host lattice can cause the magnetic fluctuations at the impurity site, and hence the stochastic change of the transition frequency of the impurity ions. It is the main source of doped ions’ optical dephasing at low temperature. Because the interactions have various time scales and strengths, they can lead to a time-dependent broadening spectral line (heterogeneous line), the process is socalled spectral diffusion. Several theoretical methods have been used to explain this phenomenon. They all divided the interactions into only two time scales, the fast one results from spin flipping of the bulk nuclei, and the slow one comes from the contributions of the nearby nuclear spins in a frozen core. However, to describe the complete dynamic process in practical systems, these two time scales are obviously not enough. In addition, spectral diffusion is a typical frequency domain process, but almost no theoretical work started from the pure frequency domain point.In this paper, the spectral diffusion in paramagnetic ions doped system at high field, in which has the modulation-frequency-dependent jump rates, is studied in both frequency and time domains. In general, the spectral diffusion goes as [1-exp(-WT_w)]^x. Without frozen core, the values of x are 1/2 and 1 for frequency and time domains, respectively. Considering frozen core effect, the spectral diffusions are slow down by the factor of (ω_eff/ω₀)², where ω₀ is the frequency characterized frozen core, and ω_eff are ω_max and H_∞ for frequency and time domains, respectively. When the frozen core is large enough, the spectral diffusions in two domains tend to have the same form as x≈0.22.