Optical Properties and Relaxation Dynamics of Type-II CdSe/ZnTe Core/Shell Quantum Dots

We perform measurements of the photoluminescence (PL) and the time-resolved PL on type-II CdSe/ZnTe core/shell quantum dots (QDs). First of all, we compare the dependence of PL and time-resolved PL on temperature and find that exciton would redistribute into larger dots at low temperature, with the recombination dominated by the radiative part. As increasing the temperature, the nonradiative part becomes dominant and the main mechanism arises from the ionization of exciton and the interaction between exciton and LO-phonon. Additionally, we observe that the radiative recombination time varies linearly with the linewidth of PL. In the measurement of excitation power dependent time-resolved PL, it is found that the radiative recombination time decreases with increasing power and may be attributed to the band bending effect due to the spatially photoexcited carriers in a type-II band alignment. In the last section, detected photon energy dependent time-resolved PL reveals that the radiative recombination time is proportional to cube of the size of QDs and this relationship may arise from the quantum confinement effect.List of Figures III 1. Introduction 1 2. Theoretical Background 7 2.1 Photoluminescence 7 2.1.1 Introduction 7 2.1.2 Principles and Applications of Photoluminescence 7 2.1.3 Apparatus of Photoluminescence Measurement 10 2.2 Band Gap and Exciton Binding Energy in Quantum Dots 13 2.2.1 Effective Band Gap of the Type-I QDs 13 2.2.2 Binding Energy of Exciton of the Type-II QDs 14 2.3 Time-Domain Lifetime 17 2.3.1 Introduction 17 2.3.2 Meaning of the Lifetime or Decay Time 18 2.3.3 Lifetimes of Band Edge Excitons in CdSe QDs 20 2.3.4 Apparatus of Time-Resolved Photoluminescence 22 3. Optical Properties and Relaxation Dynamics of Type-II CdSe/ZnTe Core/Shell Quantum Dots 32 3.1 Introduction 32 3.2 Experiments 35 3.2.1 Sample Preparation 35 3.2.2 Measurement 37 3.3 Results and Discussion 38 3.3.1 Temperature Dependent Photoluminescence and Time-Resolved PL 38 3.3.2 Excitation Power Dependent Time-Resolved PL 44 3.3.3 Photon Energy Dependent Time-Resolved PL 46 3.4 Summary 49 4. Conclusion 6