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In this project, our specific goal was to synthesize, fabricate, and investigate the spectroscopic and laser properties of various trivalent rare earth-based nanoparticles embedded in polymeric plastic host 2-hydroxyethyl methacrylate (known as HEMA).

Nd³⁺:Y₂O₃ nanoparticles embedded in poly-hydroxyethyl methacrylate, often referred to as p-HEMA, was obtained. Aggregation of nanoparticles in the HEMA matrix was prevented through sonication of the HEMA-nanoparticle solution for an adequate amount of time prior to the polymerization process. Polymerization occurs before the nanoparticles have time to fall out of the solution, thereby forming a uniform distribution of nanoparticles in the polymer matrix. The Judd-Ofelt theoretical model was applied to the room temperature absorption intensities of rare earth ions such as Nd³⁺_­(4f ³) in HEMA, to determine the three phenomenological intensity parameters: W₂, W₄, and W₆. Values are used to determine the spectroscopic quality factor for Er³⁺ in HEMA and are compared to those for Nd³⁺ ions in crystalline hosts. The intensity parameters are subsequently used to determine the spectroscopic quality factor, radiative decay rates, branching ratios and radiative lifetimes from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds ^2S+1L_J of Er³⁺_­(4f¹¹) in HEMA. Radiative lifetimes of the excited states were calculated and found to be on the same order of magnitude of those obtained for the Nd³⁺:Y₂O₃ ceramic. However, measured lifetimes were found to be longer due to re-absorption mechanisms of the Nd³⁺ ions on the surface of the particles and potential energy transfer processes between the polymer and the nanoparticles. Our results indicate that the system is capable of storing energy which can lead to low power diode and waveguide applications.

In addition, optical absorption and emission intensities are investigated for Ho³⁺ in nanocrystalline Ho^3+:Y₂O₃. Room temperature absorption intensities of Ho³⁺(4f¹⁰) transitions in synthesized Ho^3+:Y₂O₃ nanocrystals have been analyzed using the Judd-Ofelt (J-O) approach  in order to obtain the phenomenological intensity parameters. The J-O intensity parameters are used to calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios of the Ho³⁺_­ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds ^2S+1L_J of Ho³⁺_­(4f¹⁰).  The emission cross section of the important intermanifold  ⁵I₇ ® ⁵I₈ (2.0 µm) transition has been determined.  The room temperature fluorescence lifetime of this transition in Ho³⁺:Y₂O₃ nanocrystals was measured. From the radiative lifetime determined from the J-O model and measured fluorescence lifetime, the quantum efficiency of this material was determined. The comparative study of Ho³⁺_­(4f¹⁰) ions suggests that synthesized Ho^3+:Y₂O₃ nanocrystals could be an excellent alternative to single-crystal Ho³⁺:Y₂O₃ for certain applications especially in the near infrared region

We have also synthesized and characterized trivalent erbium-doped yttrium-oxide, Er³⁺:Y₂O­₃ nanocrystals. These particles were synthesized by the precipitation from a homogeneous solution. The SEM picture shows the particle size is approximately 200 nm. The room temperature optical absorption and emission spectra show that the trivalent erbium ions in Er³⁺:Y₂O­₃ nanocrystals possess sharp absorption lines and strong emission in near infrared region that are characteristic of Er³⁺:Y₂O­₃ grown as large single crystals. Also, a detailed spectroscopic analysis of the aggregates indicates that the material has optical properties similar to those reported for single crystals grown by a flame fusion method. Photostability is maintained in the nanocrystalline aggregates. The ability of these aggregates to attach to different surfaces by either chemical or physical means renders them useful in numerous technologies.

The support from the Petroleum Research Fund (PRF # 43862-B6) has been acknowledged in all papers and presentations.