Study On The Preperation Of Fluorescent Materials And Their Usages In Forensic Investigation

With the development of human society,public safety has become one of the common issues in the world.It is an urgent requirement for the realization of social security and social development to effectively control and crack down on illegal crimes.The research finds that the nano luminescent materials have potential applications in the field of criminal investigation.Nano luminescent materials have many advantages.The fluorescence excitation spectra and emission spectra can be controled by changing the size and composition of nanoparticles.The emission spectrum has a narrow half peak width,and has strong fluorescence lifetime of 100 times of organic dyes.In this paper,the nano luminescent materials were studied by means of functional materials.Two kinds of ligands Eu3+,OP and TTFA,three silicanes,TMOS,TEOS,and TKIS,were selected.Four gels have been made:TMOS(EOM,Eu3+/OP),TEOS(EOE,Eu3+/OP),TKIS(EOK,Eu3+/OP),TKIS(ETK,Eu3+/TTFA).Using sodium citrate as stabilizer,the traditional method of synthesizing the nano CdS in aqueous solution was effectively replaced by the method of sodium citrate.Europium activated strontium aluminate long afterglow materials have been made from Al2O3.SrCO3,etc.The structure and properties of the gel,emulsion and long afterglow materials were studied and characterized,and the following main results were obtained:1.Using sodium citrate as stabilizer,the traditional method to replace the large molecular tree compounds of numerous branches is effectively replaced.With the decrease of the concentration of cadmium chloride,the particle size of the cadmium sulfide nanoparticles decreases,and the color of the solution gradually becomes lighter.When the molar ratio of cadmium chloride and sodium sulfide is too low,generated emulsion instability,cadmium sulfide particles easily with a yellow precipitate,display liquid to long-term storage;high molar ratio of cadmium chloride and sodium sulfide,cadmium sulfide particles and fingerprint substances adsorption weakened,show the fingerprint fluorescence intensity decreases,ridge detail is not clear.When the molar ratio of the two in the 10:1 to 20:1,the effect is relatively stable.The solution is simple and stable,and it has good effect on the surface of the non-permeable object,and has a good effect,the sensitivity is high,and it is suitable for long time.2.Eu3+ and its ligands doped silica gel were prepared by sol-gel method.In comparison to other gels prepared,the Eu3+/OP gel prepared with TEuS as silica template has the highest fluorescence intensity and the best performance of tihe fingerprint.EuZa and its ligands in the gel pores have the same characteristic fluorescence emission spectrum as the same as in the methanol solution.The fluorescence properties of the gel and its fingerprint were still very stable after several months in the laboratory.Because of the high fluorescence intensity and fluorescence stability of Eu3+/OP gel,it becomes a kind of effective fingerprint display material.Dre to the Eu3+/OP gel in 620nm have characteristic fluorescence emission.Therefore,we chose 620nm bandwidth filters to shield the background of fingerprint ridge of interference.This gel material can be widely used in the field of textile,paper,plant leaves,metal,glass,plastic and other permeable and non permeable objects on the new potential fingerprint.For glass,metal and other smooth non permeable objects on the older fingerprint also has a better effectiveness.3.Solid phase reaction method for preparing europium activated strontium aluminate long afterglow materials can be closely integrated with the fingerprint evidence,without the need for conventional light source,for its good performance in afterglow makes use of time delay to completely shield the background interference,then obtains the traces of image become possible.Its excellent sensitivity and luminescent properties can be common permeability and non penetration object on the latent fingerprints appeared for the scene of the crime,especially the background material in the presence of fluorescent substances,highlighting its irreplaceable advantages.The results show that the nano luminescent material has the advantages of simple preparation and high detection sensitivity,and the use of non laser light source can obtain enough fluorescence intensity to detect the material evidence,and reduce the cost of criminal investigation.