Research Of Upconversion Luminescence And Temperature Sensing Properties Of Rare-earth Doped Borate

Rare earth doped upconversion luminescence materials have unique photophysical properties such as narrow emission band,long lifetime and large anti-stokes displacement,which are suitable for solid state lasers,anti-counterfeiting,temperature sensing fields.The selection of host affects the environmental stability and luminescence properties of the materials.Currently,the most widely studied fluoride host material has disadvantages such as complex preparation process,environmental pollution and poor chemical stability,which limit its practical application.Borate has the advantages of good chemical stability and high laser damage threshold,but there are few researches on borate as upconversion host materials.In this dissertation,the effects of rare earth ion doping on the crystal structure and luminescence properties of LaSc₃（BO₃）₄,Ba₃Y₂（BO₃）₄ and Ba₂Y₅B₅O₁₇ three kinds of borate-based upconversion luminescence materials were studied.The temperature sensing properties of the materials were investigated based on the fluorescence intensity ratio of non-thermally coupled energy levels.For the first time,a borate upconversion luminescent host material with tunable light color and suitable for temperature sensing applications has been discovered.The main research contents and conclusions of this thesis are as follows:（1）Yb³⁺and Er³⁺ions substitute La³⁺and Sc³⁺sites which make the cell parameters get bigger,with the increase of doping concentration the phase transformation fromα-LaSc₃（BO₃）₄ toβ-LaSc₃（BO₃）₄ and impurity phase occurs.Due to the large difference in ion radius between doped ions(Yb³⁺,Er³⁺)and replaced ions(La³⁺,Sc³⁺),the doping concentration is limited.As the doping content of Yb³⁺exceeds 0.20,the appearance of impurity phase weakens the emission intensity.（2）Yb³⁺,Er³⁺and Ho³⁺ions substitute Y³⁺sites to enter Ba₃Y₂（BO₃）₄host lattice,resulting in cell parameters reduced.With doping concentration of Yb³⁺increasing from 0 to 0.35,luminescence color of Ba₃Y₂（BO₃）₄:Yb³⁺/Er³⁺changes from green to red.The increase of doping amount of Yb³⁺enhanced the energy back transfer between activator(Er³⁺/Ho³⁺)and sensitizer(Yb³⁺),and increased the red luminescence proportion,the luminescence color of Yb³⁺/Ho³⁺doped Ba₃Y₂（BO₃）₄ show a trend of green to yellow-green.The temperature sensing performance of the material was investigated based on the fluorescence intensity ratio of un-thermally coupled energy levels,The absolute and relative sensitivity of Ba₃Y₂（BO₃）₄:0.15Yb³⁺/0.01Ho³⁺sample at 478 K were 7.54%K^-1 and1.06%K^-1,respectively.（3）The change of Ba₂Y₅B₅O₁₇:Yb³⁺/Er³⁺luminescence color from green to red is achieved by regulating the doping concentration of Yb³⁺.The temperature sensing performance of Ba₂Y₅B₅O₁₇:0.15Yb³⁺/0.01Ho³⁺sample with high luminescence intensity in the temperature range from 298K to 498 K shows that the material has potential application in the field of temperature sensing.When the temperature is 498 K,the maximum absolute and relative sensitivity of the materials reach to 9.44%K^-1 and1.19%K^-1.Compared with Ba₃Y₂（BO₃）₄,Ba₂Y₅B₅O₁₇ host material has better upconversion luminescence properties.