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

由于量子限制效应，尺寸为几纳米的半导体颗粒表现出与块体材料完全不同的性质。本研究的目的是利用光声(PA)光谱结合光致发光(PL)和光电流(PC)光谱研究(1)玻璃基质中的硫化镉和镉硒纳米晶，(2)纳米多孔二氧化钛电极，和(3)掺杂锰离子的硫化锌纳米晶(ZnS：Mn)中的光吸收特性和非辐射过程。(1)在玻璃基质中制备了不同尺寸的镉和镉纳米晶。纳米晶的最低激发能随纳米晶尺寸的增大而向低能区移动。Cd Se纳米晶的热激活能大于Cd S纳米晶。纳米晶中的超快光热信号表现出三指数行为(直接复合、激发态俘获和随后的复合过程…(2)研究了电压对高浓度电解液在纳米多孔二氧化钛电极上的作用，在带隙以下施加电压处理的纳米二氧化钛电极的功率谱强度高于未加电压处理的，表明载流子浓度增加。在禁带上方，有处理的光子晶体强度比没有处理的高，表明载流子浓度增加。随着包覆量的增加，Pc信号强度增大，能量向低能方向移动，表明纳米晶中的光激电子转移到了二氧化钛的导带上。(3)PA差谱中的峰位置随着Mn2+&gt；离子浓度的降低而增大，表明纳米晶中的S-p态与杂质中的d态杂化。在一定的离子浓度(浓度猝灭)下，荧光光谱的峰值强度出现最大值。较少

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