Control of exciton dynamics in semiconductor nanocrystals and its application in photocatalytic reaction

Abstract

Semiconductor nanocrystals (NCs) represent a class of quasi-zero-dimensional systems or quantum dots. These objects exhibit size-dependent absorption and photoluminescence (PL) spectra which result from quantum confinement effect. After exciton generated by incident light, generated electron-hole pair is recom-bined in semiconductor NCs with different timescale. This exciton carrier dynamics crucially affects to over-all optical property of NC. Therefore, we believe that it is important to understand and control exciton dynamics in NC before they are deemed a viable solution for opto-electric device or energy conversion. In this study, we discuss about understanding and control of exciton dynamics in NCs via precision control of composition, morphology, structure and surface of NCs. Based on this, we also demonstrate the relationship between carrier dynamics and photocatalytic activity of NCs. In order to control the exciton dynamics in NCs, we prepared various kinds of NCs with different composition, morphology, size and surface of NCs. The carrier dynamics of prepared NCs is measured by varying spectroscopic analysis such as transient absorption and time-resolved photoluminescence spectrosco-py. From the results, we can conclude that carrier lifetime in NCs is easily manipulated by control of size, composition, surface and band structure of NC, and this tuned carrier lifetime directly affects to photocatalytic activity of NCs. In addition, we observed that the carrier dynamics between NCs can be altered by control of assembled structure. In order to examine the carrier dynamics depending on assembled structure, we prepared various kinds of assembled clusters of nanorods (NRs), which have different inter-NR spacing. From the time-resolved photoluminescence results, it is clarify that carrier lifetime is dramatically changed by formation of assembled structure, and this change is responsible for manipulated energy transfer rate by altered inter-NR spacing. We believe this discussion will not only provide understanding of exciton dynamics in NCs, but also bring insight to use semiconductor NCs in photocatalytic applications.