Synthesis And Properties Research Of Cu-Sn-In-S Nanocrystals

Deep-red to near-Infrared(NIR)emissions(650-900 nm)are highly required for high quality indoor lighting,sensor and bio-imaging applications,respectively.In down-conversion LED devices,the deep-red and NIR light conversion materials are also indispensable.Currently,the commercialized dark-red materials are mainly rare earth doped nitrogen(oxygen)phosphors,but the preparation process of them are harsh and the cost of them are expensive.As to luminescenct semiconductor quantum dots(QDs),most of them contain class A(Cd,Pb,Hg)or class B toxic elements(Se and As).In addition The photoluminescence(PL)peaks of most QDs are narrow,and there are few reports of deep-red and near-infrared QDs,which need to be developed to make up for the vacancy.The nontoxic chalcopyrite copper indium sulfide(CuInS2,CIS)QDs have been extensively investigated since they exhibit a large absorption coefficient and tunable broad PL emissions which make them excellent candidates for white light LEDs and biological imaging etc.The PL emission of CIS QDs can be tuned and improved by strategies of adjusting Cu/In ratios and coating ZnS.In recent years,the nucleation alloying strategies have been greatly applied to tailor the optical band gaps and the emission spectra.Although deep-red to NIR emissions can be achieved in CIS QDs by increasing the Cu/In ratio,the QY(quantum yield)is too low to be applied practically.And it is very difficult to extend the maximum emission centered values of CIS QDs to the deep-red or NIR spectral range(>650nm)by coating ZnS or applying the nucleation alloying strategy(except the toxic element Se)likewise.Therefore,to realize highly efficient deep-red to NIR emissions remains a great challenge for CIS QDs.So from these discussions,we propose to obtain good deep-red to NIR emissions in Cu-Sn-In-S and Cu-Sn-In-S/ZnS QDs by incorporating Sn in CIS QDs.The main results are summarized as follows:(1)Based on the traditional synthetic method of chalcopyrite CIS,Cu-Sn-In-S and Cu-Sn-In-S/ZnS QDs with a size of 5 nm were achieved by incorporating Sn in CIS QDs.The Cu-Sn-In-S and Cu-Sn-In-S/ZnS QDs with the Cu/In=1/2 show the deep-red to NIR emission maximum in the range of 701-894 nm and 628-785 nm(in solution),respectively.(2)The amount of Sn has a huge effect on the optical properties of CIS QDs.The band gaps of CIS decrease and the PL emission peaks red-shift with increasing the amount of Sn.And a highest quantum yield of 75%is achieved in Cu-Sn-In-S/ZnS with 0.1 mmol Sn and Cu/In = 1/2 which can be attributed to the incorporation of a proper amount of Sn,which increases the proportion of ?3.According to previous studies,the longest luminescence lifetime ?3 is attributed to the donor-acceptor transition.(3)Further adjusting the Cu/In ratio,Cu-Sn-In-S/ZnS(0.1 mmol Sn)QDs show tunable deep-red to NIR emissions from 645,660,to 740 nm(in solid state).They all have higher QYs and better thermal quenching performances than their Cu-In-S/ZnS QDs counterparts.(4)Both of the white and NIR LEDs were fabricated by using Cu-Sn-In-S/ZnS QDs(0.1 mmol Sn)with different Cu/In ratios and a 365 nm LED chip.The white LED exhibits superhigh color rendering indices of Ra = 97.2 and R9 = 91 and a warm color temperature of 2700 K.And the NIR LED shows an interesting broadband near-infrared emission centered at 740 nm,allowing for applications in optical.communication,sensing and medical device.In addition,this thesis carries out related research on the zinc blende and wurtzite CIS nanocrystals(NCs).The zinc blende and wurtzite CIS NCs were successfully synthesized.The wurtzite Cu-Sn-In-S NCs and Cu1.94S-ZnS heterojunction also achieved by introduction of Sn or using Zn to replace Cu.