Sol-gel pyrolysis and photoluminescent characteristics of europium-ion doped yttrium aluminum garnet nanophosphors

Europium-ion doped Y3Al5O12 garnet nanophosphors (YAG:Eu3+) with wide ranging size tunability (40-150nm) have been prepared via a sot-get pyrolysis method employing a fuel system that combined urea and polyvinyl alcohol (PVA). Well dispersed nanoparticles were prepared at 1000 degreesC. This temperature is lower than that required for synthesizing YAG:Eu3+ via the solid-state reaction route. The particle size and morphology of the synthesized powders are found to have critical dependence on the oxidizer (metallic nitrates) to fuel ratio. The importance of using an organic polymeric dispersion matrix to obtain well dispersed YAG:Eu3+ nanoparticles has been demonstrated. The photoluminescene properties of the prepared YAG:Eu3+ phosphors are profoundly dependent on the preparation conditions. The emission intensity of well dispersed YAG:Eu3+ nanoparticles is found to be much stronger than that of the bulk sample. The excitation spectrum of well dispersed nanoparticles shows an extension of the excitation peak in the high-energy region. These unique properties of YAG:Eu3+ nanoparticles can be rationalized by considering numerous surface states due to the large surface area to volume ratio of the nanoparticles. In addition, using the hypersensitive D-5(0) --> F-7(2) transition of Eu2+ as a local probe, the role of surface states that modify the optical properties of YAG:Eu3+ nanophosphors has also been illustrated. (C) 2004 Elsevier Ltd. All rights reserved.