Study of the persistent spectral hole burning of semiconductor nanocrystals

在嵌入NaCl晶体中的CuCl量子点中观察到了发光烧孔现象，由于选择性激发，在发光光谱中出现了共振烧孔及其相应的边带。边带的斯托克斯位移可以用带负电的激子X^-和带正电的激子X_2^+的量子尺寸效应来解释。利用发光烧孔技术首次观察到量子点中新的激子复合物X^-和X_2^+，并将持续光谱烧孔（PSHB）现象成功地应用于NaCl晶体中CuCl量子点的精确择位光谱.在CuCl量子点的PSHB谱中，观察到共振烧孔和低能卫星孔。用无限高势垒量子立方体中粒子的简单概念很好地解释了共振烧蚀空穴与各卫星空穴之间的能量关系，测量了镶嵌在玻璃或碱金属卤化物晶体中的卤化亚铜量子点CuCl、CuBr和CuI中持续空穴的形成效率.玻璃中CuCl量子点在2K时获得最高量子效率0.009。在2K时，CuCl量子点的空穴谱由零声子线（线宽为0.14meV）和声子翼组成，它们之间有很好的分离。随着温度T的升高，零声子空穴与其声子边带相互融合，最终空穴谱出现展宽。与通常的激子展宽的线性温度依赖性相反，在低温下，展宽与1/ [exp（delta/kT）-1]成比例，其中delta是量子点中的受限声学声子能量。

Luminescence hole-burning phenomena were observed in CuCl quantum dots embedded in a NaCl crystal.As a result of the selective excitation, a resonantly burned hole and monreover its sidebands appear in the luminescence spectrum. The Stokes shift of the sidebands is explained by the quantum size effect of the negatively charged excition X^- and the positively charged exciton X_2^+. New exciton complexes, X^- and X_2^+, confined in quantum dots were first observed by the luminescence hole burning.A persistent spectral-hole-burning (PSHB) phenomenon was successfully applied to the precise site-selective spectroscopy of CuCl quantum dots embedded in NaCl crystals. In the PSHB spectra of CuCl quantum dots, a resonantly burned hole and lower-energy satellite holes were observed. Energy relation between the resonantly burned hole and each satellite hole is well explained by the simple concept of a particle in a quantum cube with an infinitely high potential barrier.Formation efficiencies of the persistent hole in cuprous halides quantum dots, CuCl, CuBr and CuI quantum dots embedded in glass or alkali halide crystals, were measured. The highest quantum efficiency of 0.009 was obtained at 2 K for CuCl quantum dots in glass. This high sensitivity shows the PSHB phenomenon in semiconductor quantum dots is very hopeful for the multiple optical memory device.At 2 K,the hole spectrum in CuCl quantum dots consists of a zero-phonon line (linewidth=0.14meV) and its acoustic phonon wing, and they are well separated from each other. With increasing the temperature T,the zero-phonon hole and its phonon sideband are merged to each other and finally the hole spectrum shows broadening. Contrary to the usual exciton broadening of the linear temperature dependence, the broadening is proportional to 1/ [exp (delta/kT) -1] at low temperature, where delta is the confined acoustic phononenergy in quantum dots.