Preparation And Optical Properties Of Rare Earth Doped Oxides Based On Energy Transfer Mechanism

Temperature-sensing has played a key role in our daily life in many fields such as chemistry,physics and bio-medicine.Traditional temperature measurements have many defects.For example,their applications in coal mines,a hole with a very small diameter and intracellular temperature are restricted.However,noncontact thermometers have attracted people's attention for their characters such as high temperature resistant,wide application,user-friendly and so on.To date,lanthanide-doped materials,which are often selected as non-contact thermometer based on fluorescence intensity ratio(FIR),has received great attention for their advantages such as short response time,high precision and self-reference.Oxides are excellent hosts for lanthanide-doped materials because of their stabilities,low cost and easy to get.And the appropriate energy transfer in rare-earth ions can be helpful in realizing coordinated luminescence and high-precision temperature measurement.Therefore,the main content of this paper is to design a reasonable energy transfer path in the oxides,so as to optimize the performance of rare earth doped materials.In this paper,the luminescent and temperature sensing properties of Gd₂(WO₄)₃:Er³⁺,Yb³⁺@SiO₂?LiYGeO₄:Bi³⁺/Eu³⁺/Nd³⁺were discussed respectively.The main contents of this paper are as follows:(1)The Gd₂(WO₄)₃:Er³⁺,Yb³⁺@SiO₂ were synthesized successfully by a simple one pot co-precipitation method.The morphology,phase purity and luminescent properties of the synthesized samples were characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD)and photoluminescence(PL)spectrum.The results show that in the Gd₂(WO₄)₃:Er³⁺,Yb³⁺@SiO₂ phosphors,Er³⁺ions can act as a sensitizer and transfer energy to the Yb³⁺ions under the excitation of 808 nm,then the visible and infrared luminescence can be realized through energy transfer processes between Er³⁺and Yb³⁺.Through the luminescence spectrum,the optimal doping concentration of Er³⁺and Yb³⁺ions and the effect of SiO₂ shell on the luminescence properties are discussed,and the luminescence mechanism has been determined.In addition,the temperature sensing mechanism based on Gd₂(WO₄)₃:Er³⁺,Yb³⁺@SiO₂ phosphors has been proposed,the experimental results indicate that the temperature sensing based on FIR of thermally coupled levels is more stable.(2)The LiYGeO₄:Bi³⁺/Eu³⁺/Nd³⁺phosphors are prepared by a traditional high-temperature solid-state reaction process,and the photoluminescence and thermal sensing properties are discussed in detail.Under the 254 and 310 nm excitations,the visible(?370 nm:³P₁?¹S₀)and near-infrared(?740 nm:¹P₁?³P₀)of Bi³⁺are detected in the LiYGeO₄:Bi³⁺phosphors.The 740 nm emission of Bi³⁺is consistent with the absorption of Nd³⁺,indicating that the energy can be transferred from Bi³⁺to Nd³⁺.Then,the energy transfer process between Bi³⁺,Eu³⁺and Nd³⁺is validated,and its potential applications are also mentioned.There are significant overlaps between the emission spectrum of LiYGeO₄:Bi³⁺/Eu³⁺/Nd³⁺and chlorophyll a,P_fr and PB,which indicates the phosphors can be used as plant-cultivation LEDs.Besides,the study also find that the temperature-dependent performances based on LiYGeO₄:Bi³⁺/Eu³⁺/Nd³⁺phosphors at 310 and 254 nm are different,which indicates higher S_aand S_r values at 254 nm can be obtained.