Luminescence Stability Of Cu:Zn-In-S Quantum Dots And Their LED Fabrication

Semiconductor quantum dots are widely used in display,lighting,solar cells,biomarkers and other fields because of their particle size-and composition-tunable luminescence,high emission efficiency,excellent chemical stability and other properties.With the development of science and technology,many kinds of quantum dots have been synthesized after scientists work hard.Since the low toxicity of environmentally friendly,non-heavy metal semiconductor nanomaterials are synthesized,people have focused on the application of quantum dots transferred from Cd and other heavy metal element quantum dots to new materials with low toxicity and environmental protection.In particular,quantum dots with the size-tunable emission,narrow emission width,large Stokes shift,high luminous efficiency andother optical properties,quantum dot based technology has been applied first in the field of bio-medical science.Then quantum dots are used to prepare light-emitting diodes(QD-LEDs)by researchers.Quantum dot based products are entering the market,however they can not be popularly used in the field of public lighting because of their expensive price.Although the quantum dot research is already hot,but it still suffers from some serious problems in the field of large scale production.The high synthesis cost and stability of quantum dots are two big problems that large-scale commercial production needs to be solved urgently.Therefore,the study of shell structure plays an important role in enhancing the photoluminescence properties of quantum dots,and opto-electronic performances of QD-LEDs.In this thesis,the Cu:ZnInS and Cu,Mn:ZnInS quantum dots are synthesized,and the effects of shell structure on the photoluminescence spectra and lifetimes of Cu:ZnInS quantum dots are studied.Cadmium-free doped quantum dots based white LEDs are fabricated.The novel experimental results are as follows:1.Cu:ZnInS and Cu,Mn:ZnIn S quantum dots were synthesized by one pot non-injection method.By adjusting the nucleation temperature,the ratio of Zn/In components,the amount of dopant,and the amount of precursor highly efficient quantum dots were prepared.By changing the above parameters,the Cu:ZnInS quantum dots with absorption spectra ranging from 350 to 500 nm,the photoluminescence spectra ranging from 530 nm to 630 nm,and the emission quantum yield of 60% were prepared,respectively,having a absorption band of 2.56 eV,a Stokes shift of 150 nm,luminescence quantum yield of 75% for Cu,Mn: ZnInS quantum dots.Based on the above properties of the material,the Cu,Mn-doped quantum dots can be used to prepare white LEDs for solid state lighting.2.The temperature-dependent photoluminescence spectra and decay lifetimes of Cu:ZnInS quantum dots from 80 K to 400 K were studied.It was found that the photoluminescence quenching of the bare Cu:ZnInS cores occurred at 300 K while the emission of the Cu:ZnInS/ZnS core-shell quantum dots quenched at 400 K.The temperature difference between the two samples was 100 K,which indicated that the shell structure could suppress the non-radiative recombination centers caused by surface defects.It was shown that the stability of Cu ions in doped quantum dots could be improved by increasing the shell thickness.And further the luminescence mechanism of Cu-doped quantum dots was discussed.3.The high efficiency white LEDs composed of green and red emission Cu,Mn doped ZnInS/ZnS quantum dots and blue light GaN chips were prepared.Doped semiconductor quantum dots were synthesized with a one-pot non-injection method.The color rendering index,correlated color temperature and lumen efficiency of LED devices were 95,5092 K and 73.2 lm/W,respectively.Based on the analysis of device parameters,non-toxic Cu,Mn: ZnInS quantum dots are promising to prepare white LEDs for application for daily life solid state lighting.