Study On Up-conversion Luminescence Of Erbium/Thulium Doped Tellurite Glass Microsphere

Nowadyas,the rare earth ions doped optical materials have wide applications in the fields of optical fiber communication,color display,fluorescence cooling,lasers,etc.,and the up-conversion luminescence has become a hot research topic at home and abroad.This paper combines the advantages of dielectric microsphere cavity and biconical tapered fiber,and adoptes the tapered fiber-microsphere coupled system to investigate the up-conversion luminescence of Er³⁺/Tm³⁺ doped tellurite glass microsphere.This paper includes the following research aspects:Firstly,in this paper,the basic concepts,modes matching,optical field distribution characteristics and fabrication of microsphere cavity and biconical tapered fiber are discussed.In addition,the up-conversion luminescence mechanism of rare earth ions,and influencing factors of the efficiency of up-conversion luminescence.In experiments,the up-conversion luminescence properties of Er³⁺/Tm³⁺ doped tellurite glass microsphere was experimentally studied.Firstly,the Yb³⁺/Er³⁺ co-doped tellurite glass was prepared by high temperature melting method,under the excitation of 976 nm laser with the pump power of only 3mw,intense green light was observed with the naked eyes by the tapered fiber-microsphere coupled system.The spectra at the wavelength of 522,545 and 657 nm were simultaneously detected by spectrum analyzer,which corresponds to ²H_11/2?⁴I_15/2,⁴S_3/2?⁴I_15/2 and ⁴F_9/2?⁴I_15/2 transitions of Er³⁺ ions respectively,and this process belongs to the two-photon absorption process.Secondly,the up-conversion luminescence of Yb³⁺/Tm³⁺ co-doped tellurite glass under the excitation of 976 nm laser was studied,and the blue?477nm?and red?650nm?fluorescences which corresponds to ¹G₄?³H₆,¹G₄?³F₄ transitions of Tm³⁺ ions were produced by the three-photon absorption process.In addition,the Yb³⁺/Er³⁺/Tm³⁺ tri-doped tellurite glass microsphere was prepared under the excitation of 976 nm laser,and intense white light was seen with the naked eyes,and the up-conversion luminescence spectrum of blue,green and red light were detected simultaneously.The up-conversion luminescence of rare earth has photonic applications in many fields such as background light,white light illumination,three-dimensional display,etc.The up-conversion luminescence efficiency is dependent on the concentration of RE ions,resonant enhancement,light power and environment temperature.Therefore,we further study the methods to improve the UC luminous efficiency.Firstly,the relationship between the UC luminescence efficiency intensity and various Tm³⁺concentrations was investigated,and the phenomena of concentration quenching were found.When Tm³⁺ mole fraction reached 0.3%in the Yb³⁺/Er³⁺ co-doped tellurite glass microsphere,the UC luminescence efficiency was the highest.In addition,experimental comparison of the tellurite glass's luminous efficiency in block and microsphere cavity was carried out,and the enhanced efficiency of microsphere cavity wasabout 9 times.In addition,phenomenon was discovered that the pump power and environment temperature not only had important effects on the UC luminescence,but also these would form thermo-optic effect in the microsphere.Finally,the thermo-optic effect in the microsphere cavity of different material was studied,and the changes of the whispering gallery mode?WGM?resonance spectrum by changing the pump power and temperature was observed respectively.Thermo-optic effect in silica,active tellurite glass and passive tellurite glass were measured respectively,andthe corresponding thermal optical coefficient was calculated.The study of thermo-optic effect is not only in favour of improving the stability of the microsphere cavity,and it has potential applications in the field of temperature sensing,filter,etc.