| Temperature is one of the most basic thermodynamic physical quantities.Temperature measurement is vital to many fields such as people's livelihood,engineering,medical treatment and so on.Traditional temperature measurement methods are not satisfied for harsh environments because its need contact with analyte and it takes a long time for heat to be passed to thermal equilibrium.Therefore,we are in urgent need of a non-contact,rapid response and low invironmental impact temperature measurement method.Optical thermometry techniques based on RE3+doped UC luminescent phosphors have drawn increasing attentions.Among the optical thermometry methods,the fluorescence intensity ratio(FIR)technique has attracted more attentions,since they have the advantage of independence on the spectrum loss and excitation intensity fluctuation.In this work,Er3+?Er3+/Yb3+ and Er3+/Li+ codoping Y2O3 nanoparticles(NPs)have been synthesized by low-temperature combustion synthesis(LCS).The prepared NPs are confirmed to be pure cubic Y2O3 phase with the mean size of about 40-60 nm by X-ray diffraction(XRD)analysis and scanning electron microscopy(SEM)observation.The green(2H11/2,4S3/2?4I115/2)and red(4F9/2?4I15/2)UC emissions are observed upon a 980nm excitation.By using the fluorescence intensity ratio(FIR)technique,the temperature sensing behaviors are investigated based on the thermal coupled 2H11/2 and 4S3/2 levels for Er3+?Er3+/Yb3+?Er3+/Li+ codoping Y2O3 NPs.The results demonstrate that sensor sensitivity decrease with increasing Er3+ concentration.The sensor sensitivity can be increased via codoping Yb3+ and Li+ ions and the maximum sensitivity of Y2O3:0.5mol%/Er3+/7mol%Li+ are obtained to be?0.0056 K-1 at 573K.Moreover,optical induced heating effect is also investigated.The results demonstrate that the optical heating can be avoided when the pump power below 100mW.In order to break the influence of thermal coupled levels,Y2O3:Tm3+/Yb3+ NPs is prepared by LCS.XRD,SEM and transmission electron microscopy(TEM)demonstrate that the prepared NPs are cubic Y2O3 phase with the mean size of about 40-60 nm.Strong blue(1G4(a),1G4(b)?3H6)and weak red(1G4?3F4,3F2,3?3H6)emissions are observed under 980nm excitation.Applying the FIR technique,the optical temperature sensing behaviors are studied based on thermal coupled levels((1G4(a)and 1G4(b))and non-thermal coupled levels(3F2,3 and 1G4(b)),respectively.The results show that the absolute sensitivity of non-thermal coupled levels is much higher than thermal coupled levels,the maximum absolute sensitivity is found to be as high as?0.117 K-1.Furthermore,the UC color can be modified from blue to almost white with increasing temperature.Hence,the Y2O3:Tm3+/Yb3+ NPs can be employed as the optical temperature sensor and safety sign for high temperature.We attempt to improve the absolute sensitivity using the temperature dependent luminescence of double RE ions doped materials.Y2O3:Er3+/Tm3+/Yb3+ have been synthesized by LCS.XRD,SEM and TEM demonstrate that the prepared NPs are cubic Y2O3 phase with the mean size of about 48 nm.Under a 980nm excitation,the blue(Tm3+:1G4(a),1G4(b)?3H6),green(Er3+:2H11/2,4S3/2?4I15/2)and red(Er3+:4F9/2?4I15/2)emissions are observed.The non-thermal coupled levels of 2H11/2(Er3+)and 1G4(b)(Tm3+)are studied.It found that the sensor sensitivity are increased by using non-thermal coupled levels.The maximum sensitivity values are obtained to be?0.164K-1 at 573K. |
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