Synthesis Of Metal Selenide/Telluride Quantum Dots With Photoluminescent Property Via Green Chemical Approaches

With the rapid development of nano-science and nano-technology,quantum dots(QDs)have attracted lots of attentions because of the wide potentials in bioassay,photovoltaic and thermoelectric applications,especially in light-emitting diodes and display area due to the broad absorption spectra,narrow and tunable emission spectra,near unity photoluminescence quantum yields,good physicochemical stability,and solvent processing property.These advantages make QDs proper full-color solid-state luminescent materials for both the backlight unit of liquid-crystal displays and high performance lighting sources.However,the industrial synthesis of QDs for LED applications still meets the challenge of high cost and severe pollution.In this paper,we developed facile and green methods for synthesizing high-quality QDs and investigated the formation mechanism of the QDs which would promote the further used of the QDs in lighting and display areas.In the second chapter,we demonstrate new Te precursorss for totally phosphine-free synthesis of high-quality telluride NCs.This method employs NaBH4 to reduce Te powder and subsequently dissolve Te in a series of alkylamides by moderate heating.The Te-alkylamide solution is stable enough as the precursor for hot-injection synthesis of telluride NCs,such as CdTe,HgTe,PbTe and Ag7Te4.In addition,the Te precursors are highly reactive,which permit to produce NCs at the lowered hot-injection temperature from 120 to 200 oC.Due to the high reactivity,it is facile to tailor the NC size by programming the injection temperature and the growth duration of NCs,for example controlling the diameter of CdTe NCs from 3 to 11 nm.Since the current phosphine-free synthesis is fast,facile and feasible,it will be extended to design and produce composition-and morphology-controlled telluride NCs for photovoltaic and thermoelectric applications.In the third chapter,we demonstrate a facile and feasible method to prepare phosphine-free chalcogen precursors by directly dissolving EO2(E = Se,Te)in alkylthiols.During the preparation,EO2 is reduced to E0 clusters by alkylthiols,while the alkylthiols are oxidized to disulfides.The E0 clusters further combines with disulfides,thus generating dispersible chalcogen precursors.Because of the high reactivity,the phosphine-free chalcogen precursors are suitable for synthesizing high quality CdSe and CdTe QDs under mild conditions.The as-synthesized monodispersed QDs with strong and tunable PL emission are employed as down-conversion materials to fabricate monochrome and white LEDs.TIn addition,our phosphine-free chalcogen precursors are applicable for synthesizing a variety of metal chalcogenide QDs,which will facilitate the development of industrial synthesis of QDs via cheap and environment-friendly routes.In the fourth chapter,we demonstrate a green approach for rapidly synthesizing Ag-In-Se NCs on the basis of the phosphine-free dissolution of Se powder.By controlling growth temperature,the crystal phase of Ag-In-Se NCs is tunable from metastable tetragonal phase to stable orthorhomibic phase.The In3+ doping mechanism is proposed in the formation and composition adjustment of NCs.Based on this,the composition and hence the emission color of Ag-In-Se NCs can be easily controlled.The emission is tunable from visible to NIR region,and the PLQY is comparable to that of other I-III-VI semiconductor NCs without overcoating.In comparison with the previous methods,our method is low-toxic,safe,and economical.After incorporating with polymers,the Ag-In-Se NCs can act as color conversion layer for fabricating LED devices.