Preparation And Optical Properties Of Rare Earth Ion Doped C12A7 Upconversion Materials

At present,the forbidden band width of the main material of solar cells is generally higher than 1 e V,so that sunlight below the energy value cannot be absorbed by the battery material,and the response range of the solar cell to the solar spectrum is very low,which also restricts the conversion efficiency of the solar cell.The key factor.The rare earth up-conversion luminescent material can convert the near-infrared light with a relatively long wavelength into short-wavelength light,and using the up-conversion material can help broaden the response range of the solar cell to the solar spectrum,thereby improving the conversion efficiency of the solar cell.The different doping concentrations of C12A7:Yb³⁺/Tm³⁺/Er³⁺upconversion materials prepared by high temperature solid-state method were studied.It was found that the doped rare earth ions entered the C12A7 crystal structure in a lattice substitution manner,and the change of the concentration of the doped rare earth ions did not cause obvious changes in the morphology;under the 980 nm laser excitation,the samples were at490 nm and 520 nm/550 The spectral bands at nm correspond to the blue emission of the¹G₄?³H₆ transition of Tm³⁺,the green emission of the ²H_11/2,⁴S_3/2?⁴I_15/2 transition of Er³⁺,and the spectral band at 660 nm corresponding to ⁴F_9/2?⁴I_15/2 of Er³⁺.The transition and the emission of red light from the ¹G₄?³F₄ transition of Tm³⁺are superimposed.The doping concentration of Er³⁺and Tm³⁺has a great influence on the color change of the sample.Increasing the Er³⁺doping concentration will cause the up-conversion blue-green light to weaken and increase the red light;increasing the Tm³⁺concentration will cause the blue-green light to increase and the red light to weaken.This phenomenon shows that changing Er³⁺and Tm³⁺doping concentration can affect the radiation relaxation of their own energy levels,and at the same time,it is confirmed that there is an efficient cross relaxation between Er³⁺and Tm³⁺(CR:⁴I_13/2Er+³H₄Tm?²H_11/2Er+³H₆Tm).Two groups of up-conversion materials prepared by coprecipitation were studied.?1?C12A7:Tm³⁺/Yb³⁺/Er³⁺upconversion materials with different Er³⁺doping concentrations were prepared.It was found that in this system,when the concentration of Er³⁺increases,the energy transfer between Yb³⁺and Er³⁺is promoted,the upconversion red-green light produced by Er³⁺radiation relaxation is enhanced,and the cross relaxation between Er³⁺and Tm³⁺is promoted(CR:⁴I_11/2Er+²F_3/2Tm?⁴F_7/2Er+³F₄Tm),so that the energy level of²F_3/2 of Tm³⁺is reduced,and the up-converted blue light produced by Tm³⁺radiation relaxation is reduced.As the Er³⁺doping concentration increases,the CIE color scale of the upconverted fluorescence output changes from dark blue to light blue and finally green again.?2?Preparation of C12A7:Yb³⁺/Tm³⁺/Ho³⁺upconversion material.The doped rare earth ions enter the interior of the crystal mainly in the form of lattice substitution,and did not change the original crystal structure of C12A7;the same was found from the upconversion fluorescence spectrum.In the three blue-green-red spectral bands,there are two efficient cross-relaxation processes(CR1:¹G₄ Tm³⁺+⁵I₈ Ho³⁺?³F₄ Tm³⁺+⁵F₅ Ho³⁺)and(CR2:¹G₄ Tm³⁺+⁵I₇ Ho³⁺)in this sample system.?³H₅ Tm³⁺+⁵F₄ Ho³⁺),when the Tm³⁺doping concentration increases,the cross-relaxation increases,resulting in the up-conversion blue light and red light produced by the relaxation of Tm³⁺¹G₄ energy level;at the same time,it makes the ⁵I₈ and ⁵I₇ levels of Ho³⁺.The energy is reduced,causing the up-conversion red-green light generated by Ho³⁺to decrease.From the CIE analysis,it was found that the Tm³⁺doping concentration was reduced from 0.5 mol%to 0.2 mol%,and the color of the up-converted fluorescence output changed from blue-green to light-red and finally to light blue.The C12A7:Gd³⁺/Er³⁺up-conversion material was prepared by hydrothermal synthesis method.When the Gd³⁺doping concentration was 1 mol%,the doped Gd³⁺did not change the crystal structure of C12A7 when the concentration of doped Gd³⁺was high.A new phase GdO#78-2403 will be formed,and the high Gd³⁺doping concentration will affect the crystal structure of C12A7;the red and green upconversions are found to be due to relaxation of ⁴F_9/2 and ²H_11/2/⁴S_3/2 radiations of Er³⁺,respectively.Generated(⁴F_9/2?⁴I_15/2+hv,²H_11/2/⁴S_3/2?⁴I_15/2+hv),both of which are two-photon processes,while the up-converted blue-violet light is due to the relaxation of ²H_9/2 energy levels.Produce(²H_9/2?⁴I_15/2+hv),which is a three-photon process.Increasing Gd³⁺actually enhances the energy transfer and reverse energy transfer between Gd³⁺and Er³⁺in the upconversion process.The increase in reverse energy transfer results in an increase in the energy gained by the²K_13/2 energy level,resulting in an increase in the emission intensity of the three-color upconversion.However,when the doping concentration exceeds 8 mol%,the local symmetry of the lattice field around Er³⁺is affected,and the partial Er³⁺radiation relaxation weakens,resulting in a slight decrease in the emission intensity of upconversion.With the help of energy transfer and reverse energy transfer between Gd³⁺and Er³⁺,the intensity of upconversion luminescence can be adjusted by adjusting the Gd³⁺doping concentration without changing the fluorescence output color.