Study of nonradiative processes in semiconductor nanocrystals and its applications to chemical analysis

纳米半导体颗粒由于量子限制效应而表现出与体材料完全不同的性质。本研究的目的是利用光声（PA）光谱、光致发光（PL）和光电流（PC）光谱研究（1）玻璃基质中的CdS和CdSe纳米晶体，（2）纳米多孔TiO_2电极;（3）Mn ~（2+）掺杂的ZnS纳米晶（ZnS：Mn）。(1)在玻璃基质中制备了不同尺寸的CdS和CdSe纳米晶。纳米晶的量子限制效应导致的最低激发能随着晶粒尺寸的增大而向低能区移动。CdSe纳米晶的热激活能比CdS大。CdSSe纳米晶中的超快光热信号表现出三指数行为（直接复合、从激发态捕获和随后的复合过程）。 ...更多信息 s）。(2)研究了电压对纳米多孔TiO_2电极上浓电解质的影响。在带隙以下，有电压处理的PA强度高于无电压处理的PA强度，表明载流子浓度增加。在带隙区以上，处理后的光子晶体强度高于未处理的光子晶体强度，表明载流子浓度增加。随着CdS包覆量的增加，PC信号强度增加，并向低能方向移动，表明CdS纳米晶的光激发电子转移到了TiO_2的导带。(3)PA差谱中的峰位随Mn^<2+>离子浓度的降低而增加，表明ZnS掺杂的s-p态与Mn^<2+>杂质的d态杂化。PL谱的峰强度在Mn^<2+>离子浓度的某一值处显示出最大值（浓度猝灭）。少

Semiconductor particles with sizes of a few nanometers show completely different properties from bulk materials by quantum confinement effect The purpose of this study is to show the optical absorption characteristics and nonradiative processes with the use of photoacoustic (PA) spectroscopy together with photoluminescence (PL) and photocurrent (PC) spectroscopies in (1) CdS and CdSe nanocrystals in a glass matrix, (2) nanoporous TiO_2 electrodes, and (3) ZnS nanocrystals doped with Mn^<2+> ions (ZnS : Mn).(1) Different sizes of CdS and CdSe nanocrystals in a glass matrix were prepared. The lowest excited energy of the nanocrystals by quantum confinement effect shifts to lower energy region with the increase of nanocrystal size. The thermal activation energy in CdSe nanocrystals is larger mat that in CdS. The ultrafast photothermal signals in CdSSe nanocrystals showed tri-exponential behavior (the direct recombination, trapping from excited states, and subsequent recombination processe … More s, respectively).(2) The effect of voltage on a concentrated elctrolyte applied to nanoporous TiO_2 electrodes was studied The PA intensities with the applied voltage treatments are higher than that without the treatments below the band-gap region, indicating the increase of carrier concentration. The PC intensities with the treatments are higher than that without the treatments above the band-gap region, indicating the increase of carrier concentration. The increase in PC signal intensity and a shift to lower energy are observed with the increase of CdS coating, indicating the transfer of photoexcited electrons of CdS nanocrystals to the conduction band of TiO_2.(3) The peak position in the PA difference spectrum increases with the decrease of Mn^<2+> ion concentration, indicating the hybridization of the s-p states of the ZnS nanocrystal and the d state of the Mn^<2+> impurity. The peak intensity of the PL spectrum shows a maximum at a certain value of Mn^<2+> ion concentration (concentration quenching). Less