The Investigation On 2-3 μm Near-and Mid-infrared Photoluminescence Enhancement Mechanism In Rare Earth Doped Glasses

2-3 μm near-and mid-infrared lasers have attracted wide attention due to their wide applications in military and civilian fields,such as laser guidance,infrared remote sensing,toxic gas detection and medical surgery.The gain medium is one of the most important parts of the laser.The advantages of glass materials,such as simple preparation process,short preparation cycles,and small size make them gradually replace the crystal material as the gain medium in the laser.Therefore,in recent years,the research of rare earth ions doped mid-infrared glass materials has attracted much attention.In present paper,the enhancement mechanism of near-and mid-infrared luminescence of Ho3+,Tm3+,Er3+,and Yb3+ rare earth ions doped oxyfluoride glass and fluoride glass were studied,and the main results are as follows:(1)Through gradually substituting PbF2 with ZnF2 in fluorotellurite glass(TeO2-PbF2),the hydroxyl(OH-)removal effect of ZnF2 was studied.On this basis,zinc-lead-fluorotellurite glass was prepared and its luminescent properties in mid-infrared 2.7 μm and 2.85 μm with Yb3+/Er3+ or Yb3+/Ho3+ co-doping were studied.The results indicate that as the increase in the mole fraction of ZnF2,the thermal stability of the glass increases.Moreover,the addition of ZnF2 can effectively reduce the OH-content in glass samples,and when ZnF2 completely replaced PbF2,the OH-content is only 1/3 of that of the sample without ZnF2.The minimum of the OH-in the zinc-lead-fluorotellurite glass effectively suppressesthe radiative energy transfer between OH’ and Er3+/Ho3+,consequently,the 2.7 μm and 2.85 μm mid-infrared emissions of the materials are enhanced.(2)Based on the zinc-lead-fluorotellurite glass as mentioned above,the infrared luminescent properties and the process of energy transfer between rare ions with Yb3+/Ho3+ co-doping,Yb3+/Ho3+/Er3+ triple-doping,Yb3+/Ho3+/Tm3+ triple-doping,and Yb3+/Ho3+/Er3+/Tm3+ quadruple-doping were systematically studied.The results indicate that the Yb3+/Ho3+/Er3+/Tm3+ quadruple-doping shows the strongest 2.0 μm emission enhancement under the excitation of 980nm lasers.Moreover,co-working of all the three kind of rare ions of Yb3+,Er3+ and Tm3+ enhance the 2.0 μm emission of Ho3+.Lacking of any the three ions,the best enhancement will not be achieved.In the energy transfer process,Yb3+ behaves as the most important sensitizer.Tm3+ acts as an important energy transfer ions,it can transfer a large amount of energy to the 5I7 level of Ho3+,and then promoting the emission of 2.0 μm.Er3+ will not increase the intensity of 2.0μm without Tm3+.However.when combined with Tm3+,it can transfers the energyfrom Yb3+ and the energy absorbed by itself to Ho3+ through Tm3+,thus further enhancing the 2.0 μm emission.(3)Based on fluorozirconate glass(53ZrF4-20BaF2-4LaF3-3AlF3-20NaF,ZBLAN),the luminescent properties of Tm3+ around 2.3μm were studied.The results show that as the increase in the concentration of Tm3+ in Tm3+ doped ZBLAN,the emission intensity at 2.3 μm increases firstly and then decreases due to the strong cross relaxation between 3H4 and 3H6 energy level producing the energy converge at the 3F4 level.To avoid the cross-relaxation and enhance the emission intensity of Tm3+at 2.3 μm,Bi2O3 was introduced into the glass whose Tm3+ concentration reduced.The results show that the introducing of Bi2O3 can promote the infrared emission apparently.The enhancement derives from the energy transfer between active Bi+ and Tm3+ producing the concentration of electrons in 3H4 energy level of Tm3+.