Spectroscopic Properties Of Gd³⁺/Tb³⁺ Doped Oxyfluoride Glasses

Rare earth doped glass has important applications in solid-state lasers, opticalcommunication, storage, three-dimensional display and nonlinear optics field withdifferent advantages, such as homogeneous luminescence, stable physical and chemicalproperties, low preparation cost, and can be made into a large size and various shapedevice. So the rare earth doped glass is considered to be a new kind of luminescentmaterial. Recent years, oxyfluoride glass become the research focus, because it notonly has the oxide glass characteristics of good mechanical strength, high chemical andthermal stability, but also has fluoride glass low phonon energy merit, which caneffectively enhance the RE ions luminescence efficiency. This paper mainly study thestructure of Gd³⁺/Tb³⁺ions doped LiF–MgF₂–Al₂O₃–SiO₂oxyfluoride glass, therelationship between Gd³⁺/Tb³⁺ions concentration and luminescence intensity, and theGd³⁺→Tb³⁺energy transfer mechanism. The main research contents are as follows:（1） Gd³⁺/Tb³⁺ions single doped or co-doped LiF–MgF₂–Al₂O₃–SiO₂oxyfluorideglasses were prepared by melting method, and their structures, thermal stability andlight transmission properties were studied. Silicon oxygen tetrahedron [SiO₄] andaluminum oxygen tetrahedron [AlO₄] constitute the glass structure basic networkskeleton by corner connected; Li+, Mg2+, Gd³⁺or Tb³⁺locate in the glass networkclearance; part F–ions substituted O₂–ions enter into the glass network, and the otherpart remain in the glass network clearance; Al³⁺ions main as aluminum oxygentetrahedron [AlO₄] form exist, participating in the glass network structure formation.The as-made oxyfluoride glasses have good thermal stability, anti-crystallizationability and transmission performance in the visible region with the less than360nmultraviolet absorption edge, which is propitious to the emission light transmission.（2） The fluorescence properties of Tb³⁺single doped LiF–MgF₂–Al₂O₃–SiO₂oxyfluoride glasses have been investigated. Under ultraviolet excitation, two emissiontransition of5D₃→7FJ（blue） and5D₄→7FJ（green） can be observed simultaneously atlow Tb³⁺concentration; but when the Tb³⁺concentration is higher, the5D₄levelemission intensity enhanced at the expense of that of5D₃level, because of thestrengthened of cross relaxation between5D₃→5D₄and7F₆→7F₀. So Tb³⁺ionsemission color tune from blue to green through cross relaxation in heavily Tb³⁺singledoped oxyfluoride glasses; especially when Tb³⁺concentration at3or4mol%, the Tb³⁺single doped oxyfluoride glass emits almost pure green. The Tb³⁺ions5D₄leveldecay process accords with single exponential rule; the fluorescence lifetime is ofmilliseconds magnitude with little difference in the experimental range.（3） The fluorescence properties of Gd³⁺ions single doped and Gd³⁺/Tb³⁺ionsco-doped LiF–MgF₂–Al₂O₃–SiO₂oxyfluoride glasses have been investigated. Gd³⁺ions single doped oxyfluoride glass main emits311nm ultraviolet light; theluminescence decay process fits single exponent; the fluorescence lifetime be on theorder of milliseconds, and reduced with the increasing Gd³⁺concentration. Under theexcitation wavelength of Gd³⁺ions, the characteristic emissions of Gd³⁺and Tb³⁺ionswere observed in Gd³⁺/Tb³⁺co-doped oxyfluoride glasses; it indicates the existence ofeffective Gd³⁺→Tb³⁺energy transfer that effectively improve the Tb³⁺ionsluminescence intensity. The dipole–dipole interaction is the main resonance energytransfer mechanism between Gd³⁺and Tb³⁺ions. The Tb³⁺ions5D₄level decay processfollows single exponent in Gd³⁺/Tb³⁺co-doped oxyfluoride glass; the fluorescencelifetime is of milliseconds magnitude, belongs to Tb³⁺ions typical4f→4f forbiddentransitions.