Dual-mode Luminescence Enhancement Of Er³⁺,Yb³⁺ Co-doped Phosphors Based On Energy Transfer

Phosphor materials are widely used in display lighting and biological imaging due to their advantages of high physical and chemical stability,energy saving and environmental protection,and low biological toxicity.Among them,rare earth ions doped phosphor material is playing an indispensable role in laser technology,light-emitting devices and other fields.With the rapid development of science and technology,the exploration and in-depth study of various properties and related applications of rare earth ions doped phosphor materials have become problems that scientific researchers urgently need to overcome.In order to study dualmode emission in rare earth doped phosphor materials,this thesis takes the matrix materials of aluminosilicate and garnet structures as the research objects,and uses Er³⁺and Yb³⁺as doping ions to prepare phosphors by a high temperature solid-state reaction method.The structure and luminescence properties of the phosphor materials were characterized.The main research contents are as follows:（1）LiAlSi₂O₆:Er³⁺(LAS:Er³⁺)and LiAlSi₂O₆:Er³⁺,Yb³⁺(LAS:Er³⁺,Yb³⁺)phosphors were synthesized by high temperature solid state reaction method.It indicated that the phosphors are tetragonal crystal structure and P43212 space group by XRD and FT-IR spectra.UV-Vis-NIR and PL spectra indicated that Yb³⁺ions act as sensitizers in LAS,the emission intensity of the phosphors enhanced due to energy transfer between Yb³⁺and Er³⁺ions.Under the excitation of 380 or 980 nm,the phosphors produced NIR downconversion emission at 1535 nm,the phosphors produced green（543 nm）and red（655 nm）upconversion emissions upon 980 nm or 808 nm excitation.The phosphor samples achieve highly efficient dual-mode（upconversion and downconversion）luminescence.The mechanism of energy transfer from Yb³⁺to Er³⁺was discussed in detail.（2）NaAlSiO₄:Er³⁺(NAS:Er³⁺,NASE)and NaAlSiO₄:Er³⁺,Yb³⁺(NAS:Er³⁺,Yb³⁺)phosphors were prepared by high temperature solid-state reaction method.The effects of synthesis temperature on the crystal structure and dual mode luminescence properties of NAS:Er³⁺phosphors were investigated.The synthesized phosphors were characterized by using powder XRD technique,FT-IR and UV-VIS-NIR diffuse reflectance spectra.Two different polymorphs,i.e.,nepheline and carnegieite of the NASE have been prepared just by changing the annealing temperature.The average size of NAS:Er³⁺phosphors were about several microns.PL spectra results show that the phosphors could be effectively excited by UV（380 nm）,Visible（522 nm）and NIR（980,808,or 1550 nm）and produced visible and NIR dualmode emissions.By Yb³⁺ions co-doping,the visible and NIR dual-mode emissions of NAS:Er³⁺,Yb³⁺ phosphors could effectively enhance.The energy transfer between Er³⁺and Yb³⁺ions and the possible dual-mode luminesce mechanism were explained.（3）Y₂LaCaGa₃ZrO₁₂:Er³⁺phosphors were prepared by high temperature solid state reaction method.After optimizing the Er³⁺doping concentration and reaction conditions,Yb³⁺ions were added to achieve Er³⁺,Yb³⁺ co-doped phosphors.The structure of the phosphors is stable and is assigned to the space group structure of Ia-3d by XRD and FT-IR results.The phosphors can produce Er³⁺NIR emission at 1534 nm and visible emission at 524,556,and 669 nm under excitation at 374 nm or 980 nm,respectively.Under the excitation of 374 nm Xe lamp,the phosphor can also produce emission at 972 nm,which is broadened with significantly enhanced intensity with the increase of Yb³⁺doping concentration.Under the excitation of 808 nm or 1550 nm laser,the phosphors can produce visible UC emission of Er³⁺ions.The 78～525 K temperature-dependent down-conversion emission spectra of prepared phosphors are further investigated,and the relative sensitivity of Y1.72LaCaGa3ZrO12:0.08Er³⁺,0.2Yb³⁺sample reaches the maximum value（0.93%K-1）at 300 K.In addition,the luminescence decay lifetime,energy transfer efficiency and quantum efficiency of the phosphors,as well as the possible dual-mode luminescence mechanism,are also studied.