Preparation, Structure And Properties Of Rare Earth Organic Complex Doped Silica Gel Glass

Photoactive rare earth organic complex exhibits intense narrow emission band via an effective intra molecular energy transfer from the ligands to the metal ions under excitation by near ultraviolet light due to rare earth ions' sharp intensely f-f electronic transitions and organic ligands' strong light absorbance. The practical applications of organic rare earth complexes are limited by their weakness such as thermal and photoluminescence stability. As an inorganic matrix material, silica glasses possess good optical, thermal and chemical stability, and low-temperature sol-gel process of oxide glass preparation has revealed the possibility of using this superior material as hosts for organic photoactive substances. The sol-gel process can prepare such inorganic-organic composite materials. But many rare earth organic complexes may be decomposed or hardly dissolved in sol-gel precursor solution, so that they cannot be doped in the gel glass prepared by traditional sol-gel process. This paper presents a technique of homogeneous doping the complexes in silica gel glasses called in-situ synthesis.In this study, europium and terbium ions were chosen as the rare earth ions. The photoluminescence properties and other corresponding properties of the ternary coordination complex synthesized in-situ in silica gel glasses were investigated by TG-DSC, IR spectra, XRD, SEM, excitation and emission spectra, etc. The corresponding ternary coordination complexes were also synthesized to compare with the complexes synthesized in-situ.The results indicate that such ligands as TTA and BTA, whose energy levels are matched with the ⁵D₀ of Eu³⁺, can improve the photoluminescence property of europium ion, and HBA can also improve the photoluminescence property at some degree; HBA, BTA and acac whose energy levels are matched with the ⁵D₄ of Tb³⁺, can improve the photoluminescence property of terbium ion. phen can improve the photoluminescence property of both ions, which is an excellent synergic agent.Aluminum co-doping could modify the optical properties of silica gel glasses containing the in-situ synthesized ternary coordination complex. According to the excitation and emission spectra, the optimum aluminum content could be determined as 4mol% relative to that of SiO₂ because the excitation and emission intensities of Eu³⁺ with 4mol% aluminum were the highest. On the contrary, boron content quenched the photoluminescence in the gel glass,.Ormosils could densify the gel glass and improve the mechanical properties of the gel glass, but the thermal stability was reduced simultaneously. As for MTMS and VTES, because the water-repellent organic agents were introduced, the photoluminescence properties could be improved at some degree, but the maximum contents induced should be less than 50% to avoid the opacity. GPTMS could increase the flexibility of the gel greatly and reduce the thermal stability. As for photoluminescence properties, it varied with the properties of the in-situ synthesized complexes. GPTMS could improve the photoluminescence intensity of the system such as Eu(TTA)₃phen greatly, which had stronger photoluminescence intensity. For the system such as Eu(HBA)₃phen, which had weaker photoluminescence intensity, GPTMS quenched the photoluminescence intensity on the contrary. For other rare earth organic complexes doped systems, appropriate content of GPTMS(40%～60%) could improve the photoluminescence. This may be related to the dual-purpose of the complicated organic groups of GPTMS.Considering the thermal stability, mechanical and photoluminescence properties in a whole, the optimum contents were chosen: as for gel glass containing europium ion, the contents was 50%GPTMS-50%TEOS(Eu-TTA-phen), where europium ion's concentration was 0.035%; AS for gel glass containing terbium ion, the contents was 50%GPTMS-50%TEOS (Tb-HBA-phen), where terbium ion's concentration was 0.035%.The above optimized samples exhibited high photoluminescence intensity at room temperature, but their photoluminescence decreased sharply at higher temperature. When appropriate content of aluminum was added, the photoluminescence bands of rare earths were not changed, but the photoluminescence intensity of the rare earth complex doped gel at higher temperature was improved. For gel glass containing europium ion, the appropriate content of aluminum was 0.5%, and for gel glass containing terbium ion, the appropriate content of aluminum was 2%.In manufacture and application of gel glasses containing rare earths, the appropriate contents should be chosen according to the requirement. For good flexibility and photoluminescence properties at lower temperature, 50%GPTMS-50%TEOS matrix should be chosen; for good mechanical and photoluminescence properties at higher temperature, appropriate content of aluminum should be added.The results may provide some basis to manufacture high photoluminescence, high flexibility and high thermal stability silica gel glasses in the future.