Study of the persistent spectral hole burning of semiconductor nanocrystals

观察到了镶嵌在氯化钠晶体中的CuCL量子点的发光烧孔现象，由于选择性激发，在发光光谱中出现了共振烧孔及其边带。边带的斯托克斯位移由带负电的激子X^-和带正电的激子X_2^+的量子尺寸效应解释。利用发光烧孔技术首次观察到了限制在量子点中的新的激子络合物X^-和X_2^+，并成功地将持续光谱烧孔(PSHB)现象应用于镶嵌在氯化钠晶体中的CuCL量子点的精确择位光谱。在CuCL量子点的PSHB谱中，观察到了共振烧孔和低能卫星空穴。用具有无限高势垒的量子立方体中的一个粒子的简单概念很好地解释了共振燃烧空穴和每个卫星空穴之间的能量关系。测量了镶嵌在玻璃和碱金属卤化物晶体中的CuCl、CuBr和CuI量子点中持续空穴的形成效率。玻璃中CuCl2量子点在2K时的量子效率最高，为0.009。这种高的灵敏度表明半导体量子点中的PSHB现象在多重光存储器件中是很有希望的。在2K时，CuCL量子点中的空穴光谱由一条零声子线(线宽=0.14 meV)和它的声学声子翼组成，它们彼此之间很好地分开。随着温度T的升高，零声子空穴及其声子边带相互合并，最终空穴谱变宽。与通常的线性温度关系的激子展宽相反，在低温下展宽与1/[exp(Delta/KT)-1]成正比，其中Delta是量子点中的受限声子能量。

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.