Improved Optical Degradation Characteristics of Eu Complex Encapsulated by High-Pressure Annealing

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The instability of Eu complexes against ultraviolet (UV) light irradiation is an important problem to solve before they can be practically applied in white light-emitting diodes. A novel technique of encapsulating tris(2-thenoyltrifluoroacetonato)(1,10-phenanthroline)europium(III) [Eu(TTA)3phen] was investigated using high-pressure annealing (solvothermal process) as a final process in the sol--gel synthesis. The photoluminescence and excitation spectra of encapsulated Eu(TTA)3phen samples synthesized by solvothermal and conventional annealing processes were almost the same. A half brightness time of 589 min was achieved while irradiating with UV light of 360 nm and 5 mW/cm2 by optimization of ammonia concentration and annealing temperature. The longest half brightness time was longer than that of encapsulated Eu(TTA)3phen synthesized by conventional thermal treatment. One possible reason for this result is that the chemical reaction of the sol--gel based glass network occurs more efficiently with high-pressure annealing. As a result, a high encapsulating efficiency was achieved owing to the small amount of organic component in the sol--gel derived glass network.
2011-01-25