Study On Preparation And Optical Properties Of Selenide Quantum Dots And Their Polymer Nanocomposite Films

Quantum dots（QDs）have become a new type of functional material due to their unique structural features such as quantum confinement effect,surface effect,small size effect,macroscopic quantum tunneling effect and dielectric confinement effect.At present,the preparation and applications of QDs have made great achievements and are gradually moving toward commercialization,and have shown great commercial value,affecting all aspects of people’s lives.Overview of the development of China’s QDs devices,its technology level compared to the world’s major countries still exists a large gap,and this is the key to limit its development.Increase the research and development of QDs materials is to lay the cornerstone of the development of China’s science and technology industry.As an important member of semiconductor materials,selenide is abundant in nature and has excellent photovoltaic effect,photocatalytic effect and photoconductive effect,etc.The band gap range is between 0.3-3 e V,which is a typical narrow band gap material with unique application advantages in the fields of optoelectronics,biomedicine,nonlinear optics,and electromagnetism,etc.At the same time,selenide materials have low cost in terms of price and environmental protection.In addition,selenide materials are cost effective,environmentally friendly,simple to prepare,crystalline and easy to control the size of the products.with the continuous development of material preparation technology,flexible materials are gradually becoming an important research direction.Wide color gamut,thin thickness and high efficiency light-emitting films made of QDs-polymer nanocomposite are expected to be applied in flexible devices,which are worthy of further exploration and research.In this thesis,four selenides,tungsten diselenide（WSe₂）,platinum diselenide（Pt Se₂）,tin diselenide（Sn Se₂）and germanium selenide（Ge Se）,were selected as the objects of the study,and the liquid phase exfoliation（LPE）method,a simple,inexpensive and easy to produce on a large scale.The WSe₂ QDs,Pt Se₂ QDs,Sn Se₂QDs and Ge Se QDs with uniform distribution and controllable size were prepared by grinding,ultrasound and centrifugation.The four QDs were characterized and tested by transmission electron microscopy（TEM）,X-ray diffractometer（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy（Raman）,photoluminescence spectroscopy（PL）,photoluminescence excitation spectroscopy（PLE）and ultraviolet-visible absorption spectroscopy（UV-Vis）for size morphology,structural composition and optical properties,and the four QDs were prepared with three polymers（poly（methyl methacrylate）（PMMA）,poly（vinyl alcohol）（PVA）and polydimethylsiloxane（PDMS））by blending method to obtain selenide QDs/polymer nanocomposite films,and the optical properties of the composite films were analyzed and studied by UV-Vis and PL tests,which provide a reliable basis for expanding the further applications of selenide QDs and their polymer nanocomposite films.The main work and conclusions of this thesis is as follows.（1）Four types of QDs,WSe₂ QDs,Pt Se₂ QDs,Sn Se₂ QDs and Ge Se QDs,were prepared by LPE and systematically studied in terms of size morphology,phase structure and optical properties,and the results showed that:the average particle size of all four QDs is less than 5 nm,with excellent dispersion and size distribution conforming to Gaussian distribution,XRD diffraction characteristic peaks were consistent with the standard PDF card,and the Raman characteristic vibrational peaks were obvious;the absorption in UV to IR region with absorption and strong photoluminescence properties;The PL and PLE spectra of of all four QDs showed Stokes shifts with obvious fluorescence effects,with Pt Se₂ QDs showing the best fluorescence.（2）Three Sn Se₂ QDs with average sizes of 1.9 nm,2.7 nm and 3.3 nm and two Ge Se QDs with average sizes of 2.3 nm and 3.7 nm were prepared by varying the centrifugal speed for size control of Sn Se₂ QDs and Ge Se QDs,and systematic studies of size morphology,phase structure and optical properties were carried out to explore the quantum size effects of Sn Se₂ QDs and Ge Se QDs were investigated.The results show that both QDs have significant quantum size effects.（3）A total of twenty-four QDs/polymer nanocomposite films were prepared by blending WSe₂ QDs,Pt Se₂ QDs,Sn Se₂ QDs and Ge Se QDs with PMMA,PVA and PDMS,respectively.QDs/polymer nanocomposite films were prepared by direct film formation after blending and spin coating after blending,and the optical properties of the films were investigated accordingly.By comparing the optical properties of the composite films,it can be seen that:The results show that both film-forming methods can enhance the photoluminescence and absorption performance of QDs,among which,the film-forming property of the samples prepared by co-blended direct film-forming is better,but the dispersion of QDs is not easy to control;the film thickness prepared by co-blended spin-coating film-forming method is thinner,and the dispersion of QDs is good,but the photoluminescence and light absorption performance is less enhanced.Among the twenty-four films,the best photoluminescence and light absorption performance of QDs/PDMS composite film was the most,QDs/PMMA composite film had the second best performance,and QDs/PVA composite film had the least improvement of optical performance.