Light-Emitting Polymer Nanocomposites

Inorganic nanoparticles doped with optically active rare-earth ions and coated with organic ligands were synthesized in order to create fluorescent polymethyl methacrylate (PMMA) nanocomposites. Two different aromatic ligands (acetylsalicylic acid, ASA and 2-picolinic acid, PA) were utilized in order to functionalize the surface of Tb3+？:？LaF3 nanocrystals. The selected aromatic ligand systems were characterized using infrared spectroscopy, thermal analysis, rheological measurements, and optical spectroscopy. Nanoparticles produced in situ with the PMMA contained on average 10？wt% loading of Tb3+？:？LaF3 at a 6？:？1 La？:？Tb molar ratio and ~7？wt% loading of 4？:？1 La？:？Tb molar ratio for the PA and ASA systems, respectively. Measured diameters ranged from ？nm to ？nm which is indicative that agglomerates formed during the synthesis process. Both nanocomposites exhibited the characteristic Tb3+ emission peaks upon direct ion excitation (350？nm) and ligand excitation (PA？:？265？nm and ASA？:？275？nm). 1. Introduction Rare-earth (RE) ions doped into inorganic matrices have been utilized as luminescent additives in applications such as light-emitting devices, lasers, optical amplifiers, and biological fluorescence labeling [1]. RE ions are ideal additives due to their ability to produce intense narrow spectral bands in the visible range of the electromagnetic spectrum and exhibit long excited-state lifetimes as a result of f-f electronic transitions [2, 3]. With respect to many inorganic materials, polymer matrices have the potential to offer improved production rates, lower cost, and improved processability. However, polymers exhibit inherently high vibrational energies which tend to quench many of the transitions of rare-earth ions thus limiting their application as optical materials [4]. RE ions are typically incompatible with organic polymers; although, PMMA has been shown suitable when utilized as a matrix for certain RE ion ligand complexes [5]. In this research, the method utilized to overcome high vibrational energy observed in PMMA is to incorporate optically active RE ions into low vibrational energy inorganic nanoparticles which then are dispersed into a polymer matrix by the use of selective organic ligands. The inorganic component is rare-earth ion phosphor, (terbium III), doped lanthanum trifluoride (LaF3) nanocrystals. Terbium (III) (Tb3+) emits green fluorescence as a result of a strong electronic transition, 5D4 → 7F5, occurring near 543？nm. Tb3+ exhibits absorption levels at shorter wavelengths in the ultraviolet (UV) to visible color region