Synthesis And Luminescent Properties Of Doped Silver Based Quantum Dots For Applications Of Near Infrared LED

Near infrared（NIR）light sources have exhibited great promising in food safety,environmental protection,health monitoring and bioimaging.Currently,available NIR light sources in the market including tungsten filament lamps,halogen lamps and laser diode,usually suffer from large sizes,dissipation heat and high power consumption.Solid state NIR light emitting diodes（LED）as the novel portable light-emitting device,overcomes effectively above problems.Therein,the operating principle of NIR photoluminescence LEDs mainly depends on the successful emitting of NIR fluorescence materials upon blue or ultraviolet chips.At present,the NIR activated materials employed in LEDs have been mostly carried out on transition metal ions(Cr³⁺,Mn⁴⁺,Mn²⁺etc.)activated phosphors,rare earth ions(Yb³⁺,Pr³⁺,Nd³⁺,Er³⁺etc.)activated fluorescent materials and NIR QDs（QDs）.Emission wavebands of transition metal ions doped phosphors always locate in NIR-I region due to their special energy structures.It is known that photoluminescence in the second near-infrared region（900-1700 nm,NIR-II）offers deeper tissue penetration,higher spatial resolution in comparison with the first near-infrared region（700-900 nm,NIR-I）.Rare earth elements activated materials exhibit the well-known NIR-II luminescence,but their narrow bandwidths are below than 40 nm due to the forbidden f-f transitions between 4f orbits of the rare earth ions.As a class of inorganic semiconductor material,NIR-II QDs have typical tunable NIR-II photoluminescence by adjusting the particle size and synthesis conditions,which exhibits the promising potential to be used for bio-imaging and optoelectronic devices.Previously,most of the researches on NIR-II QDs mainly focused on heavy metals Pb,Cd and Hg QDs.Compared to traditional heavy metal based QDs,Ag based QDs（Ag₂S,Ag₂Se,Ag₂Te QDs）have low biological toxicity and are friendly to the human and environment,which has been applied to the field of fluorescent biomarkers in vivo and ultra-sensitive detection direction of biomolecules in vivo.For years,doping within the QDs can be regarded as a lucrative alternative to broaden the NIR-II emission wavebands.As reported,it is an effective way to improve the luminescence intensity and broaden the emission bands of II-VI group semiconductor QDs（Zn S,Cd S,Cd Se QDs）by doping transition metal ion(Mn²⁺,Co²⁺,Cu²⁺).In this work,we have successfully the efficient achieved increasing and broadening the NIR-II luminescence properties of Ag₂X（X=S,Se）QDs by doping transition metal ion(Ni²⁺,Cd²⁺,Pb²⁺).The main research includes the following portions:（1）The preparation and the researches on luminescence properties of Ni doped Ag₂X（X=S,Se）QDs.Different concentration（0-8.0 mol%）of Ni doped Ag₂X（X=S,Se）QDs are synthesized separately by hydrothermal method.Comparing with pure Ag₂S QDs,the NIR luminescence of 6.0 mol%Ni doped Ag₂S QDs was enhanced 4.3 times stronger.Comparing with pure Ag₂Se QDs,the NIR emission of 8.0 mol%Ni doped Ag₂S QDs was enhanced 5.7 times stronger with the blue-shift of the emission peaks.The emission intensity of Ag₂Se QDs are increased efficiently.Ni doped Ag₂X（X=S,Se）QDs converted NIR LEDs were finally fabricated by coating the as-synthesized Ni doped Ag₂X（X=S,Se）QDs films on blue light chips.（2）The preparation and the researches on luminescence properties of Cd doped Ag₂X（X=S,Se）QDs.Different concentration（0-14.0 mol%）of Cd doped Ag₂X（X=S,Se）QDs are synthesized separately by hydrothermal method.Comparing with pure Ag₂S QDs,the NIR emission of 4.0 mol%Cd doped Ag₂S QDs was enhanced 3.2 times stronger.Comparing with the pure Ag₂Se QDs,the NIR emission of 4.0 mol%Ni doped Ag₂Se QDs was enhanced3.1 times stronger.The maximum full width at half maximum of 14.0 mol%Cd doped Ag₂Se QDs could reach 530 nm,which broadened significantly the NIR emission wavebands of Ag₂Se QDs.Cd doped Ag₂X（X=S,Se）QDs converted NIR LEDs were fabricated by coating the Cd doped Ag₂X（X=S,Se）QDs films on blue light chips.（3）The preparation and the researches on luminescence properties of Pb doped Ag₂Se QDs.Different concentration（0-19.2 mol%）of Pb doped Ag₂Se QDs are synthesized separately.The maximum full width at half maximum of 2.30 mol%Pb doped Ag₂Se QDs could reach 542 nm,which further broadened the emission wavebands of Ag₂Se QDs.Pb doped Ag₂Se QDs converted NIR LEDs were fabricated by coating the Pb doped Ag₂Se QDs films on blue light chips,which had shown the significant potential of vessel and tissue bio-imaging and NIR lighting.