Study On The Fluorescence Characteristics Of Lanthanum Fluoride Core-shell Nanomaterials

The fluorescence luminescence of rare earth ion-doped materials are mainly derived from the 4f-4f transition of luminescent ions.Lanthanide doped upconversion nanoparticles have been a focus in multiple application fields due to their outstanding optical features that make them a key component to various fields,which include solar cells,lighting industry,biomedicine and fingerprint identification.However,the fluorescence efficiency of the rare earth is low,which has some limits in application fields.So,the key problem is to investigate the fluorescence luminescence properties and improve the luminescence efficiency of rare earth ion-doped materials,at present.In this work,LaF₃ is used as the host material,which is known as one of the ideal host materials since its low phonon energy.Constructing core-shell structures and co-doping ions are used to study the influences of the type of the shell,the shell thickness,the doping area of Yb³⁺ ions and the ratio of Shell(Yb³⁺)/Core(Yb³⁺)on the properties of luminescence emission.The main work are as follows:The LaF₃:Ln³⁺?Ln=Er/Yb?@LaF₃ and LaF₃:Ln³⁺?Ln=Er/Yb?@LaF₃:Yb³⁺ core-shell nanoparticles were successfully synthesized by a simple hydrothermal route.And the effect of shell and shell thickness on the luminescence of LaF₃:Ln³⁺?Ln=Er/Yb?were investigated systematically.The results show that the presence of the nanoshell can segregate the surface quenching centers of the nanoparticle,then reduce the fluorescence quenching effectively.And the existence of the active shell could makes for red emission.Furthermore,the fluorescence emission of the nanoparticle can be modulate by adjusting the thickness of the shell.The distribution properties of the Yb³⁺ ions influenced upconversion luminescence of LaF₃:Er³⁺@LaF₃ core-shell nanoparticles were investigated by changing the spacial distribution of the Yb³⁺ ions and the ratio of the Shell(Yb³⁺)/Core(Yb³⁺)in core-shell particle.The results shown that the distribution properties of the Yb³⁺ ions have a great impact to luminescence.As to LaF₃:Er³⁺@LaF₃ nanostructure system,the Er³⁺ions were doped in the core.Compared with the LaF₃:Er³⁺@LaF₃ core-shell nanoparticles,which the Yb³⁺ ions doped in the shell region,the average distance between Er³⁺ ions and Yb³⁺ ions is shorter in LaF₃:Er³⁺@LaF₃ core-shell nanoparticles,which the Yb³⁺ ions doped in the core region.It is conducive to energy transfer betweel ions.When the Yb³⁺ions doped both in core and shell area,the distance between Er³⁺ ions and Yb³⁺ ions would decreased further.Thereby,both the Yb³⁺ ions can absorb the energy of the pump light and transmit it to the Er³⁺ ions to enhanced the luminescence.Furthermore,the ratio of Shell(Yb³⁺)/Core(Yb³⁺)would change the distance between Yb³⁺ ions and Er³⁺ ions and the amount of the pump energy,which can influence the luminescence of LaF₃:Er³⁺/Yb³⁺@LaF₃:Yb³⁺ core-shell nanoparticles.And constructing core-shell structure and doping the sensitizer Yb³⁺ ions in different regions can improve the co-doping threshold of Yb³⁺ ions.