Research On The Construction And Application Of Orthogonal Luminescent Upconversion Nanoplatform

Rare earth-doped upconversion nanoparticles（UCNPs）have the advantages of large anti-Stokes shifts,long fluorescence life,narrow band emission,low background fluorescence,high luminescence stability and near-infrared excitation,which make them widely used in the fields of clinical treatment,molecular detection,biological imaging,lighting display and anti-counterfeiting coding.Recently,upconversion nanoparticles have obtained excitation-emission orthogonal luminescence by using the features of Yb³⁺and Nd³⁺selectively absorbing excitation light at 980 nm and 808 nm,respectively.Different from the traditional UCNPs that obtain monochromatic luminescence under excitation at a specific wavelength,the orthogonal luminescent upconversion nanoparticles（OUCNPs）give corresponding luminescence response according to the change of excitation conditions.At the same time,these luminescence responses do not interfere with each other.In addition to traditional applications,this orthogonal luminescence properties can be applied to reversibly controlled molecular switching,security and confidentiality,color display and multiplex applications in living organisms.The core/multi-shell structure has been developed into a promising orthogonal luminescent upconversion nanoplatform,but the sensitization system of Yb³⁺and Nd³⁺in common use requires multi-layer doping,which makes the structure more complicated.Meanwhile,the long-range energy migration between layers is inevitably accompanied by the reverse energy transfer,which makes the already low luminous intensity become even lower.Based on the above problems,this paper designs an orthogonal luminescent upconversion nanomaterial with relatively simple structure and high luminescence quality（NaErF₄@Na Lu F₄@Na YF₄:20%Yb,2%Er@Na Lu F₄）,which was then used for the detection of trinitrotoluene（TNT）and simultaneous imaging display.The specific work is as follows:1.First of all,NaErF₄ nanoparticles with uniform particle size were prepared,and then three kinds of shells(Na Lu F₄,Na YF₄:20%Yb³⁺,2%Er³⁺and Na Lu F₄)were coated on its surface by Oswald ripening method,finally,OUCNPs with uniform size and good dispersion were obtained.Its characteristic is that it can realize the luminescence under808 nm excitation without Nd³⁺ion doping through 100%doped Er³⁺self-sensitization,and the reduction of the number of shells reduces the difficulty of the synthesis of OUCNPs.The energy transfer between the core and Na YF₄:20%Yb³⁺,2%Er³⁺shells is blocked by the inner layer Na Lu F₄,and the excitation energy is limited to the luminescent zone to the maximum extent,thus enhancing the luminescence intensity of the nanoparticles.The coating of the outer layer of Na Lu F₄ reduces the influence of surface factors on luminescence and again improves the overall luminescence.2.The material was optimized by adjusting the thickness of the inert shell NaErF₄（S1）.Two different luminescence modes(NaErF₄ and Na YF₄:20%Yb³⁺,2%Er³⁺)were separated into different substructures of the same nanoparticle by a certain thickness of Na Lu F₄ inert shell,and their respective functions are realized without interference:under 980 nm excitation,green light is emitted;Under 808 nm excitation,near-monochromatic red light is obtained.3.Based on the fact that the combined complex of TNT and polyethylenimide（PEI）has strong absorption at about 500 nm and can quench the green light of upconversion nanoparticles,the PEI-modified OUCNPs can be used as a self-referentially fluorescent probe to quantitatively analyze the TNT in solution,and the lower detection limit is3.04μM.Then,we prepared it into a portable test paper for TNT in-situ visual detection,showing a good visual detection effect,which is conducive to the field preliminary screening.After that,the probe was used for potential fingerprint imaging and the explosive residue TNT in the fingerprint was detected at the same time.The TNT detection is realized while the clear fingerprint is obtained.Finally,OUCNPs was used for anti-counterfeiting coding to improve the capacity and security of information.