Synthesis Of Lanthanide-doped NaYF₄ Materials With Tunable Luminescent Property And Their Application In The Construction Of Anti-counterfeiting Codes

The proliferation of fake and shoddy products has caused serious hurt to the national economy.The new packaging anti-counterfeiting technologies has become a special demand in national level for guaranteeing the economic healthy development.Due to the advantages of narrow fluorescence emission peak,photobleaching resistance,non-toxicity,without background fluorescence,the lanthanide doped upconversion fluorescent material has promising application in the field of packaging anti-counterfeiting.In recent years,multi-technology integration,especially the integration of multimedia information security technology has become the trend of developing new packaging anti-counterfeiting technology.Therefore,the upconversion fluorescent coding which combined with the novel lanthanide-doped NaYF₄ upconversion fluorescent functional material and information security technology,expected to become a new packaging anti-counterfeiting method with considerable market-competitive.However,there have three obstacles in the way of upconversion fluorescent coding practical application:(1)the low fluorescence efficiency of current lanthanide-doped NaYF₄ material,(2)the limited color tunability and fluorescence mode novelity of the current upconversion fluorescent coding materials,(3)without convenient upconversion fluorescent code detection device.This thesis aims to development of new upconversion fluorescence coding technology,and to study its application in the field of packaging anti-counterfeiting.The main research contents of this thesis include the following four aspects:1.Water-soluble,hexagonal-phase,branched NaYF₄:Yb,Er up-conversion phosphors(UCPs)were successfully synthesized by using the hydrothermal assisted with CPC(Hexadecylpyridinium chloride)and Na₃Cit(sodium citrate)(cationic/anionic)binary capping agents.The growth mechanism of the crystals in the reaction system was investigated by tracking the morphology and phase transition of the crystals and examining the effects of various reaction conditions on the morphology and crystals phase of the resultant.The result shows that the binary capping agents reduces the energy barrier of the crystal phase transition in the reaction system,and synergistic controlled the crystal morphology.The targeted adsorption of Cit³⁺on the top/bottom crystal plane will hinder the longitudinal growth of the crystal.The addition of CPC in the reaction system will attenuate the effect of Cit³⁺and induce terminal branching at an appropriate concentration.Through increasing of Yb³⁺doping amount from 10%to 98%led to the decrease of the green to red emission ratios and the resultant UCPs exhibited different emission colors ranging from green to yellow and orange.The controllable synthesis and tunable upconversion fluorescence emission of novel branched?-NaYF₄:Yb,Er crystal provide a basis for the further development of new fluorescent coding materials.2.As can be used as luminescent coding matter for construction of multicolor upconversion anti-counterfeiting barcodes,it is necessary that the matter with tunable emission light color,stable performance and good machinability.In second section,we make full use of the characteristics that the water-soluble branched UCPs is easy to combine with the polymer substrate,blended the UCPs with PVA formed a composite.Because of the intermolecular hydrogen bonds between O–H group from the PVA and pyridine ring in the CPC ligand on the surface of UCPs,the UCPs were well-dispersed in the polymer matrix and improved the thermal stability of PVA.Then,based on the red,green and blue three-color upconversion fluorescent materials and according the trichromatic additive method,multicolor lanthanide-doped NaYF₄/PVA composites with high fluorescence efficiency were prepared and used for the construction of fluorescent barcodes.The contrust barcodes were invisble in ambient light and exhibit multicolor under 980 nm laser.This covert multicolor upconversion fluorescent barcode inherited the merit of upconversion luminescent anti-couterfeiting technology and the information encryption and storage ability of barcode technology,demonstrated a promising value in anti-counterfeiting field.3.The barcode constructed by using the dual-mode fluorescent switch with an improved information dimension and storage capacity,provided an improved anti-counterfeiting level.In this paper,we proposed the synthesis of upconversion nanoparticles@carbon dots@meso-SiO₂ sandwiched core-shell nanohybrids by integrating lanthanide-doped NaYF₄ upconversion nanoparticles(UCNPs)with carbon dots(CDs)through simultaneous encapsulation of the two fluorescent materials into mesoporous silica(mSiO₂).The obtained sample possessed well-defined sandwiched core-shell structure,where mSiO₂ shell was deposited on the UCNPs and CDs were sandwiched between mSiO₂ and UCNPs.The nanohybrids possessed dual-mode fluorescence inheriting from UCNPs and CDs respectively.Ascribe to the protection of the mSiO₂ shell,the downconversion luminescence of the nanohybrids showed enhanced photobleaching resistance property upon exposed to UV light and stable luminescent property under acidic conditions.By tailoring the core UCNPs of different upconversion luminescence,we prepared three kind of dual-mode luminescent UCNPs@CDs@mSiO₂ nanohybrids which can exhibit RGB upconversion luminescence and blue downconversion luminescence.The as-prepared hydrophilic nanohybrids were fabricated into environmental benign luminescent inks for creating of secure fluorescent barcodes by inkjet printing.The constructed covert barcode composed of arranged bars and spaces can present as different colorful barcodes under the irradiation of different excitation light source,which can be read out as a three-dimension decode information.The concealment and high information storage capacity endowed the dual-mode fluorescent barcodes good candidates for application in anti-counterfeiting.4.The rapid identification of fluorescence code and the access the data center in network are the key to integrate upconversion fluorescence anti-counterfeiting technology and information security technology.The smart phone camera is used as a fluorescence image acquisition device,and a 980 nm LED and 980 nm laser are used as a near-infrared excitation light source.Combined with optical devices such as a 980nm narrow-band filter and a NIR/UV filter,a portable single-mode multicolor upconversion fluorescence code and dual-mode fulorescent code image acquisition device was builded.Based on simple and efficient digital image processing algorithms,the code information hidden in fluorescent barcode including the emission color,spatial position and the downconversion fluorescent intensity can be extract.Based on the designed hardware device and software system,the rapid detection and identification of the new single-mode and dual-mode upconversion fluorescence coding for packaging can be realized.