Synthesis Of Lanthanide-doped NaYF₄core-shell Luminescence Nanomaterials And Their Inkjet Printing

Nowadays,fluorescent anti-counterfeiting technology has been widely used in the packaging of food and commodities to resist counterfeit products and protect the rights and interests of consumers.During the past few decades,fluorescent anti-counterfeiting technologies based on the special properties of fluorescent materials emerge in endlessly,and the output mode of fluorescent anti-counterfeiting patterns is also changing with each passing day.Among the numerous fluorescent materials,lanthanide-doped fluoride nanomaterials show advantages in the field of fluorescent anti-counterfeiting due to their low phonon energy,high transmittance and good stability.Moreover,inkjet printing has been proved to be a simple,efficient,easy to scale preparation and low cost strategy for constructing of fluorescent anti-counterfeiting pattern.This thesis aims to develop advanced fluorescent anti-counterfeiting technology based on designing and synthesizing lanthanide rare earth doped fluoride nanomaterials with excellent and unique fluorescence properties,and realizing the output of high-precision and high-resolution fluorescent anti-counterfeiting patterns by inkjet printing.Specifically,this paper includes the following four parts:(1)Synthesis of Lanthanide-Ion-Doped Na YF₄RGB Up-Conversion Nanoparticles for Anti-Counterfeiting ApplicationWell-defined and mono-dispersed lanthanide-ion-doped Na YF₄up-conversion nanoparticles(UCNPs)were synthesized via thermal decomposition using lanthanide oleate as the precursor.By rational selecting the dopant pairs of the doped lanthanide ions(Y³⁺,Yb³⁺,Er³⁺and Tm³⁺)with accurate molar ratios,three-primary-color(RGB)UCNPs which exhibited green(UCNPs-G),blue(UCNPs-B)and red(UCNPs-R)fluorescence,respectively,were prepared.The X-ray diffraction(XRD)patterns showed that the three UCNPs were purely hexagonal-phase Na YF₄crystals.Transmission electron microscopy(TEM)images revealed that the synthesized UCNPs exhibited well-defined nanosphere morphology with uniform size distribution.The average diameters were23.95±3.35 nm for UCNPs-G,20.63±2.59 nm for UCNPs-B,and 19.24±2.37 nm for UCNPs-R,respectively.After surface modification employing polyacrylic acid(PAA)as modifier,the obtained UCNPs were converted to be hydrophilic,which can be used as fillers to construct luminescent polymer films and luminescent ink in anti-counterfeiting application.(2)Design of Core/Active-Shell Na YF₄:Ln³⁺@Na YF₄:Yb³⁺Nanophosphors with Enhanced Red-Green-Blue Upconversion Luminescence for Anti-Counterfeiting PrintingLanthanide-doped Na YF₄upconversion luminescent nanophosphors have attracted great interest for anti-counterfeiting applications.However,low luminescent intensity caused by surface defectsandlow extinction coefficients of lanthanide dopants greatly limits their practical applications.Herein,we developed core/active-shell Na YF₄:Ln³⁺@Na YF₄:Yb³⁺(e.g.Na YF₄:Er³⁺/Tm³⁺@Na YF₄:Yb³⁺,Na YF₄:Yb³⁺/Er³⁺@Na YF₄:Yb³⁺,and Na YF₄:Yb³⁺/Tm³⁺@Na YF₄:Yb³⁺)nanophosphors with enhanced near-infrared(NIR)-to-visible upconversion luminescence by coating Yb³⁺-doped Na YF₄shell(active-shell)on Na YF₄:Ln³⁺upconversion core nanoparticles.The structure,morphology,and elemental composition of Na YF₄:Ln³⁺@Na YF₄:Yb³⁺core/active-shell nanoparticles(CASNs),Na YF₄:Ln³⁺@Na YF₄core/inert-shell nanoparticles,and Na YF₄:Ln³⁺core nanoparticles were characterized and compared systematically to reveal their structure-property relationship.Collective data showed that coating of a Na YF₄:Yb³⁺active shell on Na YF₄:Ln³⁺cores significantly enhanced upconversion luminescent intensity by?21 times,while an inert(pure Na YF₄)shell coated on the surface of Na YF₄:Ln³⁺core only resulted in5.2 times luminescence enhancement.The enhanced upconversion luminescence intensity was mainly attributed to(i)the Na YF₄shell-reduced quenching effect and(ii)the promoted transformation of the absorbed NIR light from the pump source to the core nanoparticles by Yb³⁺sensitizer in the active shell.Moreover,by tailoring dopant pairs and molar ratios of lanthanide ions in the core nanoparticles,three CASNs with enhanced red,green,and blue upconversion luminescence were obtained and fabricated into environmental benign luminescent inks.The inkjet printing of RGB CASNs inks on papers produced multiple-color,high-resolution,complex luminescent patterns under 980 nm laser.This work expands the lanthanide-doped Na YF₄materials for anti-counterfeiting applications.(3)Design of Novel Lanthanide-Doped Core-Shell Nanocrystals with Dual Up-conversion and Down-conversion Luminescence for Anti-counterfeiting PrintingDevelopment of advanced luminescent nanomaterials and technologies is of great significance for anti-counterfeiting applications in global economy,security,and human health,but has proved to be a great challenge.To this end,we design,synthesize,and characterize mono-dispersed,dumbbell-shaped lanthanide-doped Na YF₄@Na Gd F₄core-shell nanoparticles(CSNPs)with dual-mode fluorescence by coating Na Gd F₄:Ln³⁺shell onto Na YF₄:Ln³⁺core nanospheres via a two-step oleic acid mediated thermal decomposition process.Different from conventional synthesis method to produce spherical nanoparticles,the epitaxial growth of Na Gd F₄:Ln³⁺shell onto the nanosphere cores and the lattice mismatch between?-Na Gd F₄and?-Na YF₄nanocrystals enable the formation of dumbbell-shaped CSNPs,as evidenced by the morphological evolution of CSNPs and as explained by the Ostwald ripening growth mechanism.By tailoring different doped lanthanide ions in the core and the shell,the resultant CSNPs exhibit tunable but different up-/down-conversion luminescence under the irradiation of a 980 nm laser and a 254 nm UV light,respectively.Finally,these hydrophilic CSNPs are further fabricated into environmental benign luminescent inks for inkjet printing to create a variety of dual-mode fluorescence patterns(peacock,temple,and a logo of"Hunan University of Technology")on different paper-based substrates(A4 paper,envelope,and postcard).Our dual-mode light-responsive CSNPs,along with an easy fabrication method,provide a simple and promising materials and technique for anti-counterfeiting applications.(4)Synthesis and Inkjet Printing of Na YF₄:Ln³⁺@P(GMA-co-SPMA)Core-shell Nanoparticles with Dual-mode Luminescence and Reversible Photochromic Property for Advanced Fluorescent Anti-counterfeitingIn this section,novel Na YF₄:Ln³⁺@P(GMA-co-SPMA)core-shell nanoparticles(CSNPs@p(GMA-co-SPMA))withdual-mode luminescence and reversible photochromic property were synthesized and their application in advanced fluorescent anti-counterfeiting is discussed.The CSNPs@p(GMA-co-SPMA)were synthezied by surface reversible addition-fragmentation chain transfer(RAFT)polymerization empolying glycidyl methacrylate(GMA)and N-hydroxyethyl methacrylate spiropyran(SPMA)as functional momomer in the presence of(CDPAT)functionalized Na YF₄:Ln³⁺nanoparticles.The results showed that thin p(GMA-co-SPMA)shell with pendent spiropyran group was successfully grafted onto the surface of Na YF₄:Ln³⁺nanoparticles.The resultant CSNPs@p(GMA-co-SPMA)have a uniform size of 50 nm.Due to the down-conversion luminescence and photochromic property of spiropyran group,the CSNPs@p(GMA-co-SPMA)showed dual-mode(up-/down-conversion)luminescence and reversible photochromic property.By dispersing the CSNPs@p(GMA-co-SPMA)in 1,4-dioxane,we obtained CSNPs@p(GMA-co-SPMA)luminescent ink.Advanced fluorescent anti-counterfeiting patterns were constructed on paper by inkjet printing using the CSNPs@p(GMA-co-SPMA)luminescent ink.The constructed fluorescent patterns have unique properties.In one aspect,they showed dual-mode luminescence.Green patterns can be observed under a 980 nm laser,while red patterns were observed under a 365 nm UV lamp and remove of UV lamp it still showed purple patterns under daylight.On the other hand,the fluorescent patterns exhibited reversible photochromic characteristic.Under the irradiation of 365 nm UV lamp atprolonged time interval,the fluorescent patterns gradually changed from colorless to purple,also they can reversible change from purple gradually to colorless under the irradiation of a white light at prolonged time interval.This kind of luminescent materials is anticipated to have great potential in advanced anti-counterfeiting application.