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

利用一种新发展的研究相变动力学的方法，获得了以下结果：(1).用皮秒脉冲激光研究了分子晶体蔗糖。研究发现，随着熔点的接近，荧光寿命急剧缩短。通过与X射线研究的比较，发现从低于Tm约25K的温度开始缩短是规则晶体结构向非晶态坍塌过程的标志。这将是第一次用光测量熔化转变的前驱物质。(2)生长了掺有2-萘酚(2-C8H10(0H))分子的冰(IH)单晶。荧光寿命测量表明，在130K到200K之间，寿命从5 ns递减到2 ns。用考虑了萘酚分子附近质子构型驰豫的模型分析了这种行为。这一分析使我们能够估计冰中L缺陷的产生的激活能。(3)用类似的方法研究了单晶联苯的结构相变。在转变温度T_c=40K，联苯发生二级无公度相变时，寿命出现最小值。与宽带荧光寿命的显著变化相反，在波长为533 nm处的一条尖锐的零声线具有较长的寿命，且不依赖于任何临界温度。所有这些结果都证实，本方法可以灵敏地探测与相变相关的涨落，并将能够应用于各种相变。这一结果已在第八届国际铁电会议上发表，并将在几个期刊上发表(出版并提交)。

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).