Study Of Upconversion Luminescence And Temperature Sensing Behavior Of Rare Earth Ions Doped Niobate Micro-/nanoparticles

Over the past decades,upconverting micro-/nanoparticles doped with rare-earth ions have been widely applied in the fields of laser light,three dimensional displays,fluorescence labeling,temperature sensor,bio-labeling due to their prominent luminescence?UCL?properties.At present,traditional thermometers based on the thermal contact approach are widely used for the temperature measurements.However,traditional thermometers can not match with the requirements of the measure in many cases,such as the measurement in corrosive or electromagnetic interference environment or tiny electronic fast moving objects.Compared with conventional temperature monitoring devices,the temperature sensing based on the fluorescence intensity ratio?FIR?technique guarantees the accuracy of temperature detection because it can avoid the influence of different factors of measuring conditions,resolution,and time exposure.As is known,rare earth ions posses abundant energy levels.When the energy separation is small,the higher excited state energy level can usually bethermal excitation,thus showing properties of temperature-dependent UCL,which can be used as optical temperature sensing material.In this thesis,we synthesized rare earth ions doped niobate materials through various chemical methods and studied their UCL properties as well as temperature sensing behavior.Finally,the main factors affecting the sensitivity of the optical temperature based on UCL are revealed through theoretical analysis.The main contents are as follows:?1?Yb³⁺/Er³⁺ co-doped YNbO₄ nanoparticles?NPs?were prepared via molten salt method for the first time.The results from X-ray diffraction?XRD?,field emission scanning electron microscopy?FE-SEM?,transmission electron microscopy?TEM?and high resolution transmission electron microscopy?HRTEM?indicate that the product is monoclinic phase of YNbO₄ and the average size of product is about 35 nm.The as-prepared Yb³⁺/Er³⁺ co-doped YNbO₄ NPs exhibit intense UC emissions excited by 980 nm laser diodes.Two-photon process was deduced to be main mechanism for green and red UC emissions by the analysis of power-dependent UCL intensity.The temperature sensing behavior of the as-prepared YNbO₄:Yb³⁺,Er³⁺ NPs was studied based on the FIR technique from two thermal coupled 2H11/2 and 4S3/2 levels of Er³⁺ ions.The sensor sensitivity of phosphors can be controlled by adjusting the concentration of doped ions.It was found that the sensitivity decreases with increasing Yb³⁺ concentration.Meanwhile,the UCL color can be adjusted from yellow to green with the increase of temperature.?2?A series of Yb³⁺/Er³⁺ doped NaNbO₃ micro-/nanoparticles are prepared by hydrothermal method,and the UCL properties were observed and the corresponding mechanism was proposed.The results of XRD and FE-SEM showed the product of NaNbO₃: Yb³⁺/Er³⁺ were pure phase.The UCL spectra indicate that under the 980 nm laser pumping,the phosphors doped with Yb³⁺/Er³⁺ exhibit strong green and red emission bands,which corresponds to the2H11/2,4S3/2 ?4I15/2 and 4F9/2 ?4I15/2 transitions of Er³⁺ ion.Moreover,the power-dependent UCL properties of the luminescence intensity confirmed that the green and red emission bands all caused by a two-photon process.The temperature-dependent green UCL spectrums were measured,and the temperature sensing properties of NaNbO₃ phosphors with different doped concentrations were found.The results show that the lower the Yb³⁺ doping concentration is,the higher the sensitivity of the sensor is.