用于防伪标签的发光材料研究进展(特邀)

Progress in Luminescent Materials for Anti-counterfeiting Labels(Invited)

货币、身份证件、有价证券及商品的伪造和仿制严重威胁国家政治安全、金融稳定,侵害社会团体及个人利益。防伪技术是防范和抑制造假和克隆行为的有效手段,基于发光材料的防伪标签是当前防伪领域的研究热点。本文主要介绍近年来用于防伪标签的发光材料的研究进展,包括用于防伪标签发光材料的种类、防伪材料的发光机理、实现防伪鉴别所使用的激励源、发光防伪标签的设计方法及制作技术和防伪标签的鉴别方法等。此外,本文还对当前发光防伪材料存在的问题,以及未来发展趋势作了系统分析。

The present international situation becomes complicated,and meanwhile terrorism and illegal organization activities are rampant,moreover counterfeiting and imitation of currencies,identity documents,securities,and commodities seriously threaten national political security and financial stability,and infringe on the interests of social organizations and individuals.Anti-counterfeiting technique is an effective means to prevent and suppress counterfeiting and cloning,therefore anti-counterfeiting labels based on luminescent materials turn into a research hotspot in the field of anti-counterfeiting.This review mainly introduces the research progress of luminescent materials for anti-counterfeiting labels in recent years,including the types of luminescent materials for anti-counterfeiting labels,the luminescent mechanism of anti-counterfeiting materials,the excitation sources used to realize anti-counterfeiting identification,the design method and manufacturing techniques of luminescent anti-counterfeiting labels,and the identification methods of anti-counterfeiting labels.In addition,this paper also systematically analyzes the problems existing in the current luminous anti-counterfeiting materials and the future development trend.In recent years,almost all kinds of luminescence materials have been examined to be used in anticounterfeiting labels.The more popular luminescence materials to be used include rare earth ions or transition metal ions doped inorganic phosphors,semiconductor quantum dots materials,luminescence carbon materials,metal-organic framework materials,pure organic luminescence materials,and complex and hybrid materials.The rare earth ions or transition metal ions doped phosphors exist as nano-,microcrystals,or amorphous powders.The crystals can be pure phased or core-shell structured.The amorphous powders are usually derived from the ceramic or glassy bulks via crushing or grinding processes.The semiconductor quantum dots materials that have been examined for luminescence anti-counterfeiting labels mainly include Cd-based quantum dots,lead cesium halides perovskites,and zinc oxides.In the literatures,the luminescence carbon-based materials are often defined as carbon dots,carbon nanodots,and carbon quantum dots.Up to now,there is no clear clarification for the differences between these carbon-based luminescence materials.In our opinion,these are the same.Moreover,some other luminescence carbon-based luminescence materials,like carbonated polymers and graphene have also been used in luminescence anti-counterfeiting labels.The luminescence metal-organic frameworks have also been investigated for applications of luminescence anti-counterfeiting labels.The metal specimen can be rare earth ions and transition metal ions which act as luminescence ions also.Very plentiful pure organic luminescence including cellulose,cucurbituril,polymer fiber,and small-molecule-doped organic crystals have also widely been tested for luminescence anti-counterfeiting label applications.It should be pointed out that the complex and hybrid materials composed of the above-mentioned materials are also preferable in luminescence anti-counterfeiting labels.The luminescence mechanisms for the above-stated luminescence anit-counterfeiting materials mainly contained down-shifting emission,up-conversion,long afterglow,photo-stimulated luminescence,mechano-luminescence,and delayed fluorescence.The down-shifting emissions can be achieved in the all mentioned luminescence anti-counterfeiting materials.In most cases,the excitation wavelengths are located in the ultraviolet region,and emissions full usually in the visible region.The up-conversion luminescence requires usually near-infrared wavelengths,for example,808,980,and 1150 nm,as the excitation sources,and the emissions are visible as well.The up-conversion emissions are usually realized in rare earth ions doped inorganic materials.The afterglow phosphors,photo-stimulated materials,and mechano-luminescence materials exhibit similar properties except for the excitation sources.In these materials,the defects are usually involved,and the electron and hole traps also exist and play important roles.The delayed fluorescence is usually observed in carbon-based luminescence materials and organic luminescence materials.The luminescence anti-counterfeiting labels are identified under stimuli sources.In this review,the stimuli sources used for identifications were also introduced.The stimuli sources include photo stimuli source,mechno-stimuli source,thermos-stimuli source.Amongst all these stimuli sources,the photo stimuli source is the most widely used one.The wavelengths of the photo stimuli sources contain sunlight,254,365,395,465,808,980,1060,and 1550 nm.These excitation photons usually come from ultraviolet lamps,light emitting diodes,and diode lasers.Sometimes,identification of the luminescence anti-counterfeiting labels is carried out in assistance of some chemicals,for instance,CHNHBr,HO,vinegar solution,and baking soda solution.In this review,the commonly used painting techniques for producing luminescence anti-counterfeiting labels were also presented.The widely adopted producing methods of the anti-counterfeiting labels mainly include drawing/stamping method,screen printing technique,laser jet printing technique,aerosol jet printing technique,and so on.Amongst these techniques,the drawing/stamping method is low-cost and easy-operated and is most widely used in research work.The screen printing technique is simple and mature,but the resolution of the anti-counterfeiting images produced via this technique is usually low.The laser jet printing technique is just transplanted from the laser jet printers.With the use of this technique,the inks of the laser jet printer are replaced by the inks containing the luminescence anti-counterfeiting materials.The aerosol jet printing technique is newly developed,with which three-dimensional images can be produced.At the end of this review,the present status of the luminescence anti-counterfeiting materials was concluded.The problems and obstacles to developing luminescence anti-counterfeiting labels were summarized.Some ideas for future progress were also proposed.It was figured out that the emission wavelengths for the present luminescence anti-counterfeiting materials are mainly in the visible region,thus resulting in easy counterfeiting and cloning.Therefore,developing novel luminescence anti-counterfeiting materials with emitting wavelengths other than visible wavelengths may be a good proposal.In many articles,more than one stimuli source were used,thus in fact is not a good way since the multi-excitation sources would result in complicated identification and high cost.Therefore,developing chemical-assisted luminescence anti-counterfeiting materials is more significant and meaningful.It should also be pointed out that the luminescence anti-counterfeiting materials with similar spectral properties to the commercialized phosphors are useless and dangerous since the counterfeiting and cloning behaviors are easy by using the commercialized phosphors in this sense.Finally,the combination of online and offline identifications is suggested while the 5G technique is widely used.