Upconversion-Enhanced Luminescence in PMMA Doped with Rare Earth Ions by Plasmonic Resonance with Metallic Nanoparticles.

This study investigates the luminescent dynamics of poly(methyl methacrylate) (PMMA) doped with rare earth ions, focusing on donor and acceptor ions. The acceptor ions feature two excited energy levels, enabling upconversion through energy transfer (ET) with the donor ions. Additionally, this study examines how the luminescent dynamics is affected by the enhanced electric field achieved through plasmonic resonance with metallic nanoparticles (NPs). The motivation behind this study lies in the necessity to enhance the luminescence properties of materials for advanced applications in bioimaging and optical sensors. Utilizing Förster's theory and the MNPBEM toolbox in MATLAB, the optimal NP radii for gold and silver, as well as the excitation wavelengths that maximize electric field amplification, were determined. Our findings show that silver NPs offer superior electric field enhancement (up to 8.7 times) compared to gold NPs (3.6 times). Emission amplification, influenced by the NP radius, excitation wavelength, and ion density, showed a significant correlation due to ET and excited-state absorption processes. Notably, silver NPs exhibited a maximum emission amplification of the second excited level of the acceptor ions of approximately 150 times. These findings offer valuable insights into utilizing plasmonic resonance and rare earth doping to enhance luminescent properties in materials with potential applications in biomedical imaging, biosensing, photovoltaic devices, and other advanced optical technologies. This work differs from previously published studies by focusing on the interaction of both excited-state absorption and ET in a model that considers the upconversion process and demonstrating a 2-fold higher electric field enhancement with silver NPs compared to gold. Furthermore, this study explores the optimization of NP size and excitation wavelengths to maximize the enhancement, which, to our knowledge, was not previously considered.