Molybdenum disulfide is widely used in optoelectronic devices due its properties like high mobility, effective luminescence and strong binding energy. When Molybdenum disulphide interacts with excited photons, it feasibly constructs hybrid structures in which coupling of quantum dots and monolayer Molybdenum disulfide is done effectively. During resonance energy transfer process, the absorbed photon energy is transferred to Molybdenum disulphide via nonradiative dipole–dipole interaction by the fluorescent donor, quantum dots. This yields photoluminescence in devices like solar cells, light emitting devices and photodetectors by enhancing absorptive properties of molybdenum disulfide. This energy transfer process is temperature dependent and therefore a group of researchers led by Professor Baojun Li from Sun Yat-Sen University in China studied the thermal process of both structures quantum dots / molybdenum disulfide. The research work is published in peer-review journal, Nano Research.
The CdSe–ZnS core–shell quantum dots and monolayer Molybdenum disulfide (MoS2) structures fabricated using spin-coating method were investigated for energy transfer. This investigation of energy transfer from CdSe–ZnS core–shell quantum dots to monolayer molybdenum disulfide involved measurement of Photoluminescence spectra and decay curves in the temperature range of 80 400 K.
The quantum dots that are excited via laser excitation, transfer photon energy to molybdenum disulfide resulting in photoluminescence quenching of quantum dots. The Photoluminescence peak intensity of quantum dots decrease with increase in temperature whereas it increases for molybdenum disulfide. Hence quenching happens in quantum dots. The decreased decay time of quantum dots showed the fact that resonance energy transfer is responsible for its emission changes. Hence resonance energy transfer is responsible for both photoluminescence quenching and decreased decay time.
The authors observed as the temperature increases, strong decrease in peak density and larger shift in peak position of photoluminescence for quantum dots in structures than those in quantum dots. This indicates more energy loss during energy transfer from quantum dots to molybdenum disulfide in quantity dot structures. The photoluminescence decay time is dependent on characteristic time of energy transfer process, radiative decay time and nonradiative decay time as well. The ratio of number of electron hole pairs generated in quantum dots to the number of absorbed photons denotes the quantum efficiency which is higher in quantum dots of substrate than those in structures. The energy transfer efficiency and the energy transfer rate is found to increase when the temperature is between 80 and 260 K and decrease until 400 K.
The dipole-dipole resonance coupling between the core–shell quantum dots and the monolayer Molybdenum disulfide depends on the magnitude of the wave vector. Hence the energy transfer process is affected by the population of localized excitons in quantum dots structures. At low temperature, low efficiency is achieved due to dominant role of localized excitons in the energy transfer process. As temperature is increased from 80 to 260K, there is increase in the energy transfer efficiency and the energy transfer rate. After exceeding 260K, the wave vector of free excitons is too large to achieve efficient coupling and hence resonance energy transfer rate and efficiency decreases until 400K. This change in efficiency and rate of energy transfer process is due to its dependency on transition from localized to free excitons of quantum dots in quantum dots / molybdenum disulfide structure. The results of this study contribute to better design of optoelectronic devices based on QDs/MoS2 nanostructures.
Juan Li, Weina Zhang, Yao Zhang, Hongxiang Lei, and Baojun Li, Temperature-dependent resonance energy transfer from CdSe_ZnS core_shell quantum dots to monolayer MoS2, Nano Research, Volume 9, 2016, Pages 2623–2631.
State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou, China
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