| The up-conversion luminescence of rare earth ions doped transparent host materials have become a research hotspot at home and abroad,because it has wide applications in fields of up-conversion lasers,anti-Stokes fluorescence cooling,color display,etc..Among many host materials,oxyfluoride glass ceramic is one of materials which attracted much attention because it possesses low phonon energy and high chemical and mechanical stability simultaneously,so it conducive to the realization of up-conversion.The light in the equatorial inner surface of the microsphere cavity will exhibit total reflection because of the whispering gallery modes(WGM),which makes tiny coupling power achieve light of high power density,so the microsphere cavity possess the features of low mode volumes and ultra-high quality factor.The biconical tapered fiber is a good coupler for both coupling pump laser into microspheres and extracting light emission from them with high coupling efficiency.In this article,the combination of the characteristics of oxyfluoride glass ceramic and microsphere was proposed.We have employed biconical tapered fiber-microsphere coupled structure to investigate the luminescence properties of the rare earth ions doped oxyfluoride glass ceramic microsphere cavity,and this method has characteristics of easy operation and test.Firstly,the Yb3+/Er3+ co-doped oxyfluoride glass was prepared by high temperature melting method,and annealed at an appropriate temperature to form the glass ceramic materials.We discussed the microcrystalline structure of oxyfluoride glass ceramic by analyzing the X-ray diffraction(XRD)and transmission electron microscopy(TEM)images.The results show that the glass matrix generated LaF3 crystal phase after the heat treatment,then the average size of crystalline grain was about 27.76 nm according to the Scherrer’s formula.Subsequently,this article studied the up-conversion luminescence properties of Yb3+/Er3+ co-doped oxyfluoride glass ceramic microsphere,under the excitation of 976 nm laser,the spectrum at the wavelength of 522,545 and 657 nm were detected simultaneously,which correspond to 2H11/2→4I15/2,4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ ions,and the intense green light was seen with the naked eyes.In addition,the laser oscillation spectrum at 1562 nm generated from Er3+ ions was also detected.Finally,the up-conversion luminescence mechanism of Yb3+,Er3+,the mechanism of high luminescence efficiency in Yb3+/Er3+ co-doped oxyfluoride ceramic microsphere and the mechanism of higher laser oscillation threshold in the oxyfluoride glass ceramic microsphere than in the SiO2 matrix microsphere are all analyzed in this article.On the other hand,this article further investigated the luminescence properties of the Tm3+/Er3+/Yb3+ tri-doped oxyfluoride glass ceramic microsphere under the excitation of 976 nm laser.Firstly,the three primary colors,i.e.blue,green and red fluorescence which is the composition of white light was detected.Yb3+ ion in the Tm3+/Er3+/Yb3+ tri-doped oxyfluoride glass ceramic microsphere acts as a sensitizer,which transfer the energy to the Tm3+,Er3+ ions,then the up-conversion luminescence efficiency was greatly increased.Subsequently,this article introduced the linear relationship between the luminous flux of white light and pump power through the measurement of the luminous flux meter.Finally,the up-conversion luminescence mechanism and the reason of high luminescence efficiency were analyzed.Compared with the white light produced by fluorescent powder under the excitation of ultraviolet LED,the white light obtained by up-conversion under 976 nm laser can overcome some disadvantages,which has potential applications in many fields such as background light,lighting,etc. |
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