Optical And Luminescence Properties Of Europium Ions In Inorganic Sol-gel And Polymer Optical Films

Over the past few decades, much attention has been devoted towards rare-earth ionsdoped optical films, which were used for developing optical devices such as solid-state lasers,fiber amplifiers, infrared to visible up-converters and field emission displays. Compared withfine grain luminescent powders, phosphor films exhibit superior thermal conductivity, higherdegree of uniformity and better adhesion factor.In this work, Eu³⁺-doped inorganic sol-gel and polymer optical films were designed.Optical and luminescence properties of Eu³⁺ions in the films have been studied at roomtemperature. The results and progresses obtained are as follows:1. High concentration Eu³⁺-doped amorphous titanate （KBT） luminescence film, whichemits bright red light under the excitation of the UV light, has been successfully fabricated viasol-gel method. Excitation and three-dimensional fluorescence spectra analysis indicates thatEu³⁺-doped KBT film can be induced effectively under the excitation of the UV light due tothe absorption of the charge transfer band of Eu-O. Typical Eu³⁺emission peaks wereobserved in the fluorescence spectrum and the strongest emission at about616nm with redcolor corresponds to the5D07F2transition. Based on Judd-Ofelt theory, the optical intensityparameters2and4derived from the emission spectrum were6.92×10^-20cm²and1.84×10^-20cm², respectively, and the total radiative transition rate （272.5s1） along with theradiative lifetime （3.67ms） of the5D0exciting state were calculated. The stimulated emissioncross-sections σ and the fluorescence branch ratios β for the5D07FJ（J=1,2,4） transitionswere also obtained.2. Eu³⁺-doped Y_xTi_1-xO_1-0.5x（YTO） crystal film was spin-coated on quartz glasssubstrates through sol-gel route. XRD results revealed that the film was made up ofY_xTi_1-xO_1-0.5xgrains with cubic structure in average size about17nm. Typical Eu³⁺emissionpeaks were observed in the fluorescence spectrum and the strongest emission with red colorcorresponds to the5D07F2transition. Based on Judd-Ofelt theory, the optical intensityparameters2and4derived from the emission spectrum were4.02×10^-20cm²and2.17 ×10^-20cm², respectively, and the total radiative transition rate （979.8s1） along with theradiative lifetime （1.02ms） of the5D0exciting state were calculated. The stimulated emissioncross-sections σ and the fluorescence branch ratios β for the5D07FJ（J=1,2,4） transitionswere also obtained.3. Eu（TTFA）₃-doped epoxy-based negative photoresist polymer film has beensuccessfully fabricated and the photoluminescence properties of the chelate complex wereinvestigated. TTFA has been proved to be a good ligand of Eu³⁺for red emissions and thefilm can be excited effectively in a broadband UV radiation range from200to400nm.Moreover, efficient complex interaction and energy transfer from ligand TTFA to Eu³⁺havebeen exposed and interpreted by electron-effect and energy-matching mechanism. Energytransfer mechanism in the absorption processes for the red Eu³⁺emissions was discussed andthe “antenna effect” between rare earth ions and ligand was confirmed again. Based onJudd-Ofelt theory, the optical intensity parameters Ω₂and4derived from the emissionspectrum were24.4×10^-20cm²and2.8×10^-20cm², respectively, and the total radiativetransition rate (977s^-1) along with the radiative lifetime （1.02ms） of the⁵D₀exciting statewere calculated. The stimulated emission cross-sections σ and the fluorescence branch ratios βfor the5D07FJ（J=1,2,4） transitions were also obtained.These new phenomena and results of studies provide the theoretical basis and pledge ofnew materials for new types of optical devices, such as optical waveguides, sensors anddisplays.