Theoretical And Experimental Study Of Upconversion Luminescence Of Er, Yb And Tm Doped Borosilicate Glasses

The trivalent ions with abundant energy levels of rare earth elements exhibit considerable potential applications in optical temperature sensor,shortwave laser, biomedicine diagnostics and white-light illumination,etc,because of their upconversion luminescence.Firstly,a series of samples of Er³⁺-doped,Yb³⁺:Er³⁺ co-doped and Yb³⁺:Er³⁺:Tm³⁺ co-doped borosilicate glasses with different doping concentration were prepared by high-temperature melting,respectively,and the technical parameters were optimized.Secondly,the absorption and photoluminescence spectra of the samples of Er³⁺-doped and Yb³⁺:Er³⁺ co-doped borosilicate glasses were measured.The J-O intensity parametersΩ_k(k=2,4,6),spontaneous radiative lifetimeÏ„_rad,spontaneous transition probability A,fluorescence branching ratioβand the stimulated emission cross-sections of the up-conversion red,green emission for the trivalent Er³⁺ ions were calculated based on Judd-Ofelt theory and McCumber theory.The J-O intensity parameterΩ₂ become smaller with the increasing of erbium concentration for the single Er³⁺-doped borosilicate glasses.But for the Yb³⁺:Er³⁺ co-doped borosilicate glasses,the value ofΩ₂ become bigger with the increasing of ytterbium concentration,and bigger than that of silicate,fluorid and bismuth glasses reported,which means the borosilicate matrices being stronger covalence behavior.The increase of Yb³⁺-doped concentration not only improves the activity of Er³⁺ ions,but also increases the stimulated emission cross-sections of the Er³⁺ upconversion emission at 521nm and 651nm,benefiting the advance of efficiency for Er³⁺ upconversion emission.Thirdly,the photoluminescence spectra of Yb³⁺:Er³⁺:Tm³⁺ co- doped borosilicate glasses were measured in the range from ultra-violet to near infrared at room temperature,using a 978nm laser diode as an excitation source.The dominate up-conversion mechanisms,including energy transfer,cross relaxation and excited state absorption were discussed.The up-conversion emissions of Er³⁺ ions at 369nm,399nm, 523nm,537nm,659nm and 800nm are excited mainly by 978nm from semiconductor laser.But the upconversion emissions of Tm³⁺ ions at 474nm and 788nm are excited by an unexpected wavelength,900nm,emitting from Yb³⁺ Stark splitting levels.The power spectra at 474nm,788nm and 900nm take on the same trend.In particular,the intensities of the three spectra start to decrease when the pumping power exceeds 324mW because the efficiency of the energy transfer from Yb³⁺ to Er³⁺ is effectively enhanced,leading to the decrease of 900nm emitting.Therefore,the so-called "power quenching" phenomenon happens.At the same time,the temperature characteristics of Er³⁺:Yb³⁺:Tm³⁺ co-doped borosilicate glasses was investigated.With the increasing of the samples temperature, both green and red upconversion luminescence intensities at 523nm,537nm and 659nm become weak gradually,even approximately disappear at 490K.However,the luminescence intensity of 900nm becomes stronger and stronger,and its peak wavelength shifts to shortwave direction.At last,the work of the thesis was summarized,and future research plans have been prospected for rare earth doped materials.