Up-conversion Luminescent Materials Design On NaYF₄ Doped With Pr³⁺/Yb³⁺ And Its Preparation,Characterization

Up-conversion luminescence is a process in which the electrons within the material absorb two or more low-energy photons to emit a high-energy photon after transition,accumulation and downward transition,which will convert the infrared photons into visible photons or even ultraviolet photons.At present,the study on up-conversion luminescent materials in the fluorescence field has gotten more attention,and the concentration of rare earth ion doping is one of the decisive factors which affecting the up-conversion luminescence efficiency.In this paper,the discussion focuses almost exclusively on the luminescent properties of Pr³⁺/Yb³⁺co-doped NaYF₄ up-conversion luminescent materials.The systems of NaYF₄ doped with Pr³⁺ions are studied by the simulation software of Materials Studio.The structures of hexagonal phase are not broken after Pr³⁺ion doping.The unit cell parameters increase slightly and the density of states shift to the direction of low energy level.As to one of the doping systems,a new peak appears at the fermi level,and the band gap reduced,which is conducive to the electron transition.Moreover,the absorption rate of the doped systems increases and the reflection coefficient decreases in infrared wavelengths,which is advantageous for up-conversion luminescence.Hydrothermal method is used to prepare NaYF₄:Pr/Yb up-conversion phosphors with different concentrations.The morphology of the crystal is intact with uniform size.Under excitation of 980 nm and 808 nm laser,samples appear yellow-green and white fluorescence respectively.Under excitation of 980 nm laser,the luminescence peaks of each sample are located at 486 nm,522 nm,542 nm and 657 nm,respectively.And the four luminescence processes are all two-photon processes.Under excitation of 808 nm laser,the luminescence peaks of each sample are located at 516 nm,672 nm and 729 nm,respectively.And the three luminescence processes are all two-photon processes.And all the luminescence peaks corresponding to energy level lifetime reach up to hundred microseconds level,long up-conversion luminescence lifetime means longer stay at this energy level and better luminescent property.Under excitation of 1064 nm laser,the luminescence of samples are not visible.The emission spectra have only one strongly characteristic luminescence peak at 804 nm,and luminescence process is two-photon process,and the luminescence peak of each samples corresponding to the energy level lifetime reach to ten microseconds.The fluorescence lifetime is short,but because of the uniqueness of its characteristic luminescence peak,it has potential application value in the field of up-conversion fiber lasers.Comparing the emission spectra under three excitation conditions above-mentioned,sample No.2?NaYF₄:3%Pr,20%Yb?shows the best up-conversion luminescence properties.