Multi-color Luminescence In Single Nanocrystals

The main feature of the rare earth doped up-conversion luminescence material is that it can emit visible light under the excitation of near-infrared light.Compared with organic dyes or quantum dots,rare earth doped up-conversion luminescence materials have obvious advantages,such as large spectral shift,long fluorescence lifetime,narrow emission bandwidth,relatively low cost,etc.,and thus are widely used in solid-state lasers,biomarkers,solar cells,anti-counterfeiting security,temperature sensing and other fields.Despite the above advantages,the traditional up-conversion materials still have two major defects of low luminescence intensity and lack of dynamic color adjustment.A conventional scheme capable of significantly improving luminescence efficiency and realizing multi-color emission is to construct a core-shell structure,passivate the surface defects of the nanocrystals to improve luminescence efficiency,and spatially separate different activators in different regions,and realize multi-color luminescence by adjusting laser power.However,most of the core-shell structures that achieve multi-color luminescence are excited by a single laser and require high excitation power,so they are not suitable for use in the biological field.In addition,current systems typically implement color adjustment based on blue and green light,and there are few reports of using red light as the primary color for multi-color adjustment.In order to solve the above problems,the following work is done in this paper.First,a highly efficient single-band red-emitting core-shell NaErF4@NaYF4 nanocrystal was prepared.At 980 nm and 1530 nm laser excitation,the luminescence intensity of the same quality nanocrystals reaches a maximum at a ratio of core to inert shell of 1:2,while the red-green ratio increases with the thickness of the inert shell.The test results show that the sample has higher luminescence efficiency under laser excitation at 1530 nm.In addition,the up-conversion luminescence mechanism of nanocrystals in two pumping modes was analyzed based on the power dependence of luminescence intensity.Secondly,core-multishell nanocrystal with high purity dual-color luminescence were prepared by epitaxial growth using core-shell NaErF4@NaYF4 nanocrystals as seeds.By constructing a core-shell structure,a functional layer that dominates different color emissions is integrated on a single nanocrystal to achieve red/green emission on a single particle nanocrystal.Its specific structure is NaErF4@NaYF4@NaYF4:18Yb/2Er@NaYF4.In addition,a single-particle nanocrystal(NaErF4@NaYF4@NaYF4:20Yb/0.5Tm@NaYF4)with red/blue light emission was also constructed.The luminescence properties of nanocrystals were systematically investigated,and their independent emission of characteristic color light at 980 nm and 1530 nm dual laser excitation was realized.Finally,the color output was fine-tuned in real time by adjusting the power of the two lasers,and the anti-counterfeiting demonstration was performed using the prepared nanocrystals.Finally,a compact nanocrystal capable of achieving capable of panchromatic luminescence at the single particle level was prepared.Its specific structure is as follows:NaYF4:18 Yb/0.5Tm@NaLuF4@NaYF4:40Er@NaLuF4@NaYF4:1Nd/1Yb/0.5Er.Compared with the previous two multi-color luminescence nanocrystals,this material has a more luminescence color tunability.The three primary colors of red,green and blue are respectively radiated under the excitation of three kinds of lasers,so that panchromatic luminescence can be realized by adjusting the excitation power of the three lasers.