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

荧光晶体熔化跃迁前驱现象及弛豫过程的研究

基本信息

批准号：
04640329
负责人：
SHIGENARI Takeshi
金额：
$ 1.6万
依托单位：
THE UNIVERSITY OF ELECTRO-COMMUNUCATIONS
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

项目摘要

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).

采用一种新的研究相变动力学的方法，得到了以下结果。(1).A用皮秒脉冲激光对分子晶体蔗糖进行了研究。发现荧光寿命随着熔点的接近而急剧下降。通过与X射线研究的比较，发现从低于Tm约25 K的温度开始观察到的缩短的开始是规则晶体结构到非晶态的塌陷过程的指示。这将是第一次通过光测量熔融转变的前兆。(2)生长了掺杂2-萘酚（2-C8 H10（OH））分子的冰（Ih）单晶。荧光寿命的测量结果表明，在130 ~ 200 K温度范围内，荧光寿命从5 ns逐步减小到2 ns.分析使我们能够估计的活化能的生成的L-缺陷的冰。(3)用类似的方法研究了联苯单晶的结构相变。在转变温度Tc= 40 K时，联苯的寿命出现最小值，此时联苯发生二级无公度相变。与宽带荧光寿命的显著变化相反，λ = 533 nm处的零声子谱线具有相当长的寿命，而不依赖于临界温度，所有结果都证实了本方法可以灵敏地探测与相变有关的涨落，并能应用于各种相变。研究结果已在第八届国际铁电会议上发表，并将发表在几本杂志上（出版和提交）。e.g.in