| Rare earth doped upconversion nanomaterials can absorb long wavelength photons and emit short wavelength photons,which are widely concerned in many fields such as biology,display,anti-counterfeiting and so on.At the same time,because of its rich luminescent color and efficient luminescent performance,it has become a hot spot in the field of up conversion research.For a long time,many scholars have done a lot of research on improving the up conversion luminous intensity.In the aspect of luminous color regulation,in order to avoid repeated synthesis,the dynamic polychromatic regulation of a single material is the ideal state of luminous materials.In this paper,three kinds of upconversion nanoparticles with uniform core-shell structure have been synthesized.Ca2+ doping improves the intensity of upconversion luminescence,Ce3+as the center of cross relaxation,Gd3+as the energy medium to realize the efficient upconversion luminescence of Eu3+,and realize the dynamic polychromatic adjustment of the material in the pulse width and laser power adjustable excitation.These three kinds of core-shell structures are expected to be applied in the fields of anti-counterfeiting and display.The specific research contents are as follows:1.NaYF4:Er/Ho/Ca@NaYF4 double-layer core-shell nanoparticles were synthesized,and their morphology and luminescent properties were characterized.In the double-layer core-shell structure,the doping of Ca2+ increases the size of nanoparticles and makes the morphology more uniform.In terms of luminescence enhancement,Ca2+ doping can improve the luminescence intensity of Er/Ho combination under 980 nm excitation by changing the crystal field around lanthanide ions.In terms of luminescent color regulation,the doping of 0.5%Ho3+improves the red emission level of NaYF4:10Er,and the introduction of Ho3+ increases the filling time difference between green and red energy levels of the system.As the pulse width of 980 nm increases,the luminescent color changes from green to red gradually,realizing the dynamic color regulation of a single material excited by 980 nm with different pulse width.2.Three-layer core-shell nanoparticles of NaYF4:Yb/Tm@NaYF4:Yb/Ho/Ce@NaYF4:Yb/Nd were synthesized.The effect of cross relaxation on upconversion luminescence was studied.In the three-layer core-shell structure,the Nd3+ sensitized layer not only absorbs 808 nm excitation energy,but also passivates the surface defects of nanoparticles to enhance the luminescence.The doping of Ce3+ leads to three effective cross relaxation processes,which makes the color of Ho3+change from green to red.In addition,the cross relaxation changes the up conversion energy transfer path of Ho3+,which makes the red light weaken under the excitation of short pulse width 808 nm,and the system realizes dynamic color regulation under the excitation of pulse width adjustable 808 nm.3.Synthesized NaGdF4:Eu@NaGdF4:Yb/Tm@NaGdF4:Yb/Nd/Er three-layer core-shell nanoparticles were used to study the up conversion energy transfer mode of rare earth ions doping.In the three-layer core-shell structure,the upconversion of Eu3+under 808 nm excitation is realized by using Gd3+as the transfer medium of upconversion energy.To the same nanoparticle.We put Er3+,Tm3+ and Eu3+ in different shells respectively.According to the energy level matching degree and energy transfer mode of different activator ions and sensitizer ions,we realized the luminescent regulation that the system changed from green to cyan and finally to red with the increase of 808 nm power density. |
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