| InP/ZnS core-shell quantum dots not only have similar optical properties as Cd-based and Pb-based quantum dots,but also have lower toxicity.Therefore,it has huge potential in the fields of optical limiter,solar cell,light-emitting diode,and biomedical imaging.It will be guided the synthesis and application by researching In P/Zn S quantum dots.However,the synthesis of high-quality In P/Zn S quantum dots with stable chemical properties started relatively late,and there are few reports on the research of In P/Zn S quantum dots,especially in photo-physical properties.In this paper,the femtosecond pulsed laser,nanosecond pulsed laser and continuous laser are used as laser sources.The photo-physical properties of In P/Zn S quantum dots are researched using Z-scan technology,temperature photoluminescence detection technology and transient absorption technology.The obtained photo-physical properties are mainly in three aspects as follows.The nonlinear optical properties of InP/ZnS core-shell quantum dots toluene solution showed that In P/Zn S core-shell quantum dots exhibited saturated absorption and self-focusing with femtosecond pulse excitation.It was attributed to the Kerr effect of electrons.The saturation intensity was obtained which was 6×1013W/m2,and the nonlinear refraction coefficient was about 0.45×10-19m2/W.The ground state absorption cross-section was gotten which was about 1.16×10-17cm2.The switch from saturated absorption to reverse saturated absorption and self-defocusing were observed with nanosecond pulse excitation.The mechanism of the switch was attributed to excited-state absorption,and self-defocusing was attributed to the thermal effect.In addition,the excited-state absorption cross-section was obtained which was 35×10-17cm2,the excited-state lifetime was obtained which was 82 ps,and the nonlinear refraction coefficient was obtained about-1.6?±0.2?×10-15m2/W.The photoluminescence properties of InP/ZnS quantum dots showed that the peak position redshifted,the line width broadened,and the intensity decreased with the temperature increasing from 80K to 300K under the excitation of 405nm continuous laser.The photoluminescence peak was red-shift with temperature increasing which mechanism was attributed to the interaction of excitons and longitudinal acoustic phonons,and the longitudinal acoustic phonon energy 22 me V was obtained.The linewidth of photoluminescence was broadened with temperature increasing which came from the contribution of both the exciton-longitudinal acoustic and exciton-optical phonon interaction,and the longitudinal optical phonon energy 41 me V was obtained as well.The intensity of photoluminescence was decreased with temperature increasing which were attributed to two energy loss processes.One was the interaction of excitons and longitudinal acoustic phonons,and the other was the interaction of excitons and multiple longitudinal optical phonons.In addition,at the same temperature,the bandgap energy of excitons increased,the strength of exciton-longitudinal acoustic phonons coupling increased,the strength of exciton-longitudinal optical phonon coupling decreased with the size of In P/Zn S quantum dots decreasing.With 190 fs pulse excitation,up to 4 excitons were observed under the intensities from 6.9×103W/m2to 1.8×105W/m2.The lifetime of 1-exciton was 4.4 ns,2-exciton was 43 ps,3-exciton was 9.7 ps,and 4-exciton was 3.65 ps respectively.The relationship between the lifetimes??n?and the number?n?of excitons obeyed?n-1=1/2n2?n-1?+n/?1.Under incident intensities of 1.8×105W/m2,average 3.4 excitons per quantum dot can be generated by absorbing multiple 400 nm photons.These results will provide theoretical and practical significance to understand the photo-physical properties of In P/Zn S quantum dots deeply,promote the application of In P/Zn S quantum dots in the field of optical information,and guide the synthesis of InP/ZnS quantum dots. |
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