Studies on the precursor phenomena and the relaxation processes of melting transitions of crystals by a fluorescence

采用一种新发展的相变动力学研究方法，得到了以下结果：(1)。用皮秒脉冲激光对蔗糖分子晶体进行了研究。发现随着熔点的接近，荧光的寿命急剧下降。通过与x射线的对比，发现在低于Tm约25K的温度下开始观察到的缩短表明了规则晶体结构向非晶态的坍塌过程。这将是光对熔化转变前兆的首次测量。(2)得到了掺杂2-萘酚（2- c8h10 (0H)）分子的单晶冰（Ih）。荧光寿命测量表明，在130K和200K之间，荧光寿命从5ns逐渐减少到2ns。用考虑萘酚分子邻域质子构型弛豫的模型分析了这种行为。通过分析，我们可以估计出冰中l -缺陷产生的活化能。(3)用类似的方法研究了单晶联苯的结构相变。寿命在转变温度Tc=40K时最小，此时联苯发生二级不相称相变。与宽带荧光寿命的显著变化相反，λ =533nm处的尖锐零声道线具有相当长的寿命，没有任何临界温度依赖性。结果表明，该方法可以灵敏地探测与相变相关的波动，并能适用于各种相变。研究结果已被报道，例如在第8届国际铁电会议上，并将出现在几本杂志上（已出版和提交）。

Using a newly developed method for the studies on the dynamic of phase transitions, the following results were obtained.(1).A molecular crystal 'Sucrose' was investigated with a pico-second pulsed laser. It was found the lifetime of the fluorescence sharply decreases as the melting point is approached. By comparing with the X-ray study, it was found that the onset of the observed shortening from a temparature about 25K below Tm was an indication of the collapsing process of the regular crystal structure into an amorphous state. This would be the first measurement of a precursor of a melting transition by light.(2) A single crystal of ice(Ih) doped with 2-naphthol(2-C8H10(0H)) molecules was grown. The fluorescence lifetime measurements recealed that a stepwise decrease of lifetime from 5ns to 2ns occurs between 130K and 200K.The behavior was analyzed by a model which takes into account the relaxation of the proton configurations in the neighborhood of the naphthol molecules. The analysis allowed us to estimate the activation energy for the generation of L-defects in ice.(3) A structural phase transition of a single crystal biphenyl was investigated by a similar method. The lifetime shows a minimum at the transition temperature Tc=40K, where biphenyl undergoes a second order incommensurate phase transition. In conrast to the significant change in the lifetime of the broadband fluorescence, a sharp zero-phono line at lambda=533nm was found to have a rather long lifetime without any critical temperature depenedence.All the results confirmed that that the present method can be a sensitive probe of fluctuations associated with the phase transitions and would be able to be applied to variety of phase transitions. The results were reported, e.g.in the 8th International Meeting on Ferroelectricity and will appear in several journal(in press and submitted).