To enhance the reproducibility and scale up the synthesis of colloidal quantum dots(QDs),continuous flow synthesis is an appealing alternative to the widely used batch synthesis.Amongst other advantages,the strongly e...To enhance the reproducibility and scale up the synthesis of colloidal quantum dots(QDs),continuous flow synthesis is an appealing alternative to the widely used batch synthesis.Amongst other advantages,the strongly enhanced heat and mass transfer in small tubular reactors combined with controlled pressure can be cited.Nonetheless,the widespread use of this technique is hampered by special requirements such as the absence of solid or gaseous products and the room-temperature solubility of precursors.Therefore,the transfer of established reaction conditions from batch to flow is not straightforward and in most reported works the optical properties of the obtained QDs lag behind those prepared in batch reactions.This is also the case for PbS-based QDs,which are established near infrared(NIR)absorbers/emitters.Here we identified experimental conditions giving access to high-quality PbS core and PbS/CdS core/shell QDs obtained in an automated,easily scalable continuous flow synthesis.In particular,substituted thioureas have been selected as the sulfur source and ex-situ synthesized lead and cadmium oleate as the metal precursors,and appropriate solvent mixtures have been identified for each precursor.Highly luminescent PbS/CdS QDs emitting at the target wavelengths 940 and 1130 nm of special interest for NIR light-emitting diodes have been prepared,exhibiting a photoluminescence quantum yield up to 91%.展开更多
Optical properties and ultrafast exciton relaxation dynamics in PbS and core/shell PbS/CdS quantum dots(QDs) have been studied using UV-vis absorption and fluorescence spectroscopy as well as femtosecond(fs) transient...Optical properties and ultrafast exciton relaxation dynamics in PbS and core/shell PbS/CdS quantum dots(QDs) have been studied using UV-vis absorption and fluorescence spectroscopy as well as femtosecond(fs) transient absorption spectroscopy.The electronic absorption spectrum of the PbS QDs features broad absorption in the entire near IR-vis-UV region with a monotonic increase in intensity towards shorter wavelength.Relative to PbS,the absorption of the core/shell PbS/CdS QDs shows a slight blue shift in the 600?800 nm region,due to the decrease of the PbS crystal size caused by the synthetic process of the core/shell structure,and increased absorption near 400 nm due to the CdS shell.The PL of the PbS/CdS QDs was ~2.6 times more intense than that of the PbS QDs,due to surface passivation of PbS by CdS,and blue-shifted,attributable to smaller PbS size and thereby stronger quantum confinement in the core/shell QDs.Fs transient absorption measurements of both systems showed a strong transient absorption feature from 600 to 750 nm following excitation at 750 nm.The transient absorption decays can be fit to a biexponential with time constants of 8 and 100 ps for PbS and 6 and 80 ps for PbS/CdS.The amplitude and lifetime of the fast component were excitation intensity dependent,with the amplitude increasing more than linearly with increasing excitation intensity and the lifetime decreasing with increasing intensity.The fast decay is attributed to exciton-exciton annihilation and it occurs more readily for the PbS/CdS than the PbS QDs,which is attributed to a lower density of trap states in the core/shell QDs,as supported by their stronger PL.展开更多
基金platforms of the Grenoble Instruct-ERIC center(ISBGUAR 3518 CNRSCEA-UGA-EMBL)within the Grenoble Partnership for Structural Biology(PSB)+1 种基金supported by FRISBI(ANR-10-INBS-0005-02)financed within the University Grenoble Alpes graduate school(Ecoles Universitaires de Recherche)CBH-EUR-GS(ANR-17-EURE-0003).
文摘To enhance the reproducibility and scale up the synthesis of colloidal quantum dots(QDs),continuous flow synthesis is an appealing alternative to the widely used batch synthesis.Amongst other advantages,the strongly enhanced heat and mass transfer in small tubular reactors combined with controlled pressure can be cited.Nonetheless,the widespread use of this technique is hampered by special requirements such as the absence of solid or gaseous products and the room-temperature solubility of precursors.Therefore,the transfer of established reaction conditions from batch to flow is not straightforward and in most reported works the optical properties of the obtained QDs lag behind those prepared in batch reactions.This is also the case for PbS-based QDs,which are established near infrared(NIR)absorbers/emitters.Here we identified experimental conditions giving access to high-quality PbS core and PbS/CdS core/shell QDs obtained in an automated,easily scalable continuous flow synthesis.In particular,substituted thioureas have been selected as the sulfur source and ex-situ synthesized lead and cadmium oleate as the metal precursors,and appropriate solvent mixtures have been identified for each precursor.Highly luminescent PbS/CdS QDs emitting at the target wavelengths 940 and 1130 nm of special interest for NIR light-emitting diodes have been prepared,exhibiting a photoluminescence quantum yield up to 91%.
基金supported by the Basic Energy Sciences Division of the US DOE (DE-FG02-ER46232)
文摘Optical properties and ultrafast exciton relaxation dynamics in PbS and core/shell PbS/CdS quantum dots(QDs) have been studied using UV-vis absorption and fluorescence spectroscopy as well as femtosecond(fs) transient absorption spectroscopy.The electronic absorption spectrum of the PbS QDs features broad absorption in the entire near IR-vis-UV region with a monotonic increase in intensity towards shorter wavelength.Relative to PbS,the absorption of the core/shell PbS/CdS QDs shows a slight blue shift in the 600?800 nm region,due to the decrease of the PbS crystal size caused by the synthetic process of the core/shell structure,and increased absorption near 400 nm due to the CdS shell.The PL of the PbS/CdS QDs was ~2.6 times more intense than that of the PbS QDs,due to surface passivation of PbS by CdS,and blue-shifted,attributable to smaller PbS size and thereby stronger quantum confinement in the core/shell QDs.Fs transient absorption measurements of both systems showed a strong transient absorption feature from 600 to 750 nm following excitation at 750 nm.The transient absorption decays can be fit to a biexponential with time constants of 8 and 100 ps for PbS and 6 and 80 ps for PbS/CdS.The amplitude and lifetime of the fast component were excitation intensity dependent,with the amplitude increasing more than linearly with increasing excitation intensity and the lifetime decreasing with increasing intensity.The fast decay is attributed to exciton-exciton annihilation and it occurs more readily for the PbS/CdS than the PbS QDs,which is attributed to a lower density of trap states in the core/shell QDs,as supported by their stronger PL.
