Preparation And Optical Properties Of ?-NaYF4:Ce3+,Tb3+,Sm3+/Opal Photonic Crystals

Lanthanide doped fluorescent particles have always been attached great importance.Rare earth fluoride,especially NaYF₄,as a good luminescent matrix material,shows obvious advantages,such as low phonon energy,high refractive index,effectively reducing the multi-photon relaxation process,reducing the energy loss of non-radiative transition,etc.,so it has been widely used.Photonic crystals(PCs)are man-made materials with ordered structure,which are formed by periodic arrangement of materials with different refractive indexes in space.The most significant feature of the optical control is Bragg scattering effect caused by periodic structure.In order to solve the problem of low transfer efficiency of rare-earth doped nanoluminescent materials,photonic crystals are used to enhance fluorescence intensity of rare-earth doped nanoluminescent materials to study,and the luminescence efficiency and luminescence intensity of rare-earth doped luminescent materials are enhanced from the perspective of structural design.It is of great and profound significance not only to explore the underlying physical mechanism behind the fluorescence enhancement but also to the experimental application.The results are as follows:(1)In this paper,soap-free emulsion polymerization method was used to prepare monodisperse polymethyl methacrylate(PMMA)microspheres with uniform properties and size,and then the three-dimensional opal photonic crystal was prepared by vertical sedimentation self-assembly method.The morphology of the samples was characterized by scanning electron microscope(SEM).Using ultraviolet-visible near infrared spectrophotometer transmittance measurement of multiple sets of samples.Results showed that the preparation of PMMA three-dimensional opal photonic crystal band gap of the sample position achieved from 360 nm to 1000 nm.(2)With Ce³⁺as sensitizer to assist luminescence,Tb³⁺and Sm³⁺as activators of luminescence center,Ce³⁺,Tb³⁺and Sm³⁺rare earth ions were added to NaYF₄matrix respectively for the first time,and?-NaYF₄:Ce³⁺,Tb³⁺and Sm³⁺nanocrystals with different doping concentrations were prepared by solvothermal method.The X-ray diffraction pattern of the sample is in good agreement with the standard card,and the trimixing of Ce³⁺,Tb³⁺and Sm³⁺in the experimental concentration range does not change the crystal structure of NaYF₄.Under the excitation of 248 nm laser,the down-conversion emission spectrum of the sample showed blue,green and red light.Corresponding to 5d-4f of Ce³⁺,~5D₄?~7F₆,~5D₄?7F₅,~5D₄?~7F₄,~5D₄?~7F₃ of Tb³⁺and ~4G_5/2?~6H_5/2,~4G_5/2?~6H_7/2,~4G_5/2?~6H_9/2 of Sm³⁺,respectively.The energy transfer mechanism and photoluminescence properties of Ce³⁺?Tb³⁺,Tb³⁺?Sm³⁺,Ce³⁺?Sm³⁺,Ce³⁺?Tb³⁺?Sm³⁺were discussed.(3)?-NaYF₄:Ce³⁺,Tb³⁺,Sm³⁺nanocrystals were dispersed in cyclohexane,and a layer of?-NaYF₄:Ce³⁺,Tb³⁺,Sm³⁺nanocrystals was grown on the surface of PMMA opal photonic crystals(OPCs)by self-assembly method to construct ?-NaYF₄:Ce³⁺,Tb³⁺,Sm³⁺/PMMA composite films enhance the emission intensity30 times by adjusting the band gap position of PMMA opal photonic crystal.SEM scanning showed that?-NaYF₄:Ce³⁺,Tb³⁺and Sm³⁺nanocrystals were deposited in the gaps of photonic crystal microspheres.Due to the coupling of photonic band gap and emission field of photonic crystal and the light amplification caused by random scattering of light on the surface of PMMA microspheres,efficient fluorescence enhancement was observed on them.