Fabrication of CdS/ZnS and CdS/CuS Composite Quantum Dots Having Controlled Optical Properties
제어된 광학적 특성을 갖는 CdS/ZnS와 CdS/CuS 복합체 양자점의 제조
- 자연과학대학 화학부
- Issue Date
- 서울대학교 대학원
- quantum dots; alloy; lattice mismatch; radiative recombination; nonradiative recombination; carrier relaxation; transition metal doped quantum dots; energy transfer efficiency
- 학위논문 (석사)-- 서울대학교 대학원 : 화학부, 2013. 2. 장두전.
- In this dissertation, stable and luminescent CdxZn1-xS alloy and Cu-doped CdS quantum dots were synthesized by aqueous route and characterized using a combination of optical and structural characterization techniques.
In chapter 1, we have synthesized chemical composition gradient CdxZn1-xS quantum dots by using facile cation exchange procedure to as-prepared CdS quantum dots. By controlling the ratios of [Zn] to [Cd], composition variable GCdxZn1-xS (x = 0.13~0.92) QDs have been synthesized. Due to the shell effect of ZnS, the as-prepared GCd1-xZnxS QDs possess higher QY and longer lifetime than CdS QDs. Also, we have prepared other 2 types of QDs having different inner structure, same size and similar composition with GCd1-xZnxS, CdS@ZnS core-shell (CCd1-xZnxS), homogeneous Cd1-xZnxS alloy (HCd1-xZnxS) QDs. (Fig. 1-1). Then, the impact of their inner structure on the carrier relaxation dynamics has been discussed. We have studied the decay dynamics by using time-resolved spectroscopy and analyzed the decay curves using multi-exponential decay function. Finally, we propose a stochastic model to estimate the radiative and nonradiative relaxation rate and the number of trap states and compare these decay parameters with experimental data. Finally, we try to correlate the radiative and nonradiative relaxation rates and the number of trap states with lattice strain developed in Cd1-xZnxS alloy QDs.
In chapter 2, we prepared 4 types of CdS:Cu(2%) QDs but, each of them were synthesized in different synthetic ways. 4 strategies were designed: center doping, homogeneously doping, cation exchanged-doping, and adsorption respectively. synthetic route-dependent optical properties of 2% Cu-doped CdS(CdS:Cu(2%)) QDs have been discussed. we gained the photoluminescence (PL) decay curve by using time-resolved spectroscopy and analyzed the decay curves using multi-exponential decay function. we have obtained the efficiency of energy transfer from an exciton inside the CdS core to a Cu ion (ΦET) and the efficiency of the emission from the Cu ion (ΦCu) by using the undoped photoluminescence (PL) quantum yield (QY) and the Cu-related PL QY. By comparing these factors, it has demonstrated that doping location in the host QDs affect energy transfer and radiative recombination of QDs.