Sol-gel derived siloxane-encapsulated nanoparticle hybrid composite for highly stable wavelength converting materials

Abstract

Nanoparticles, for example upconversion-nanoparticles (UCNPs), quantum-dots (QDs), colloidal anocrystal clusters, and photonic crystals, are promising materials as wavelength converters because these have unique properties such as large Stokes or anti-Stokes shift, sharp emission bands, low autofluorescence. To be practically applied to opto-electronic devices, they should be directly encapsulated or coated on the devices. For fabricating encapsulants or coatings, the nanomaterials should be made of resin mixed with binder. However, formation of resin with binder for fabricating polymer composites face a couple of formidable roadblocks: (i) poor dispersion of nanoparticles in polymer

and (ii) deteriorating optical properties of the composites. In addition to the dispersion problem, optical properties of the nanoparticle/polymer composites decreases over time, particularly when the film is exposed to heat, oxygen, or moisture. In this thesis, nanoparticle encapsulated by siloxane matrix is reported for highly stable wavelength converting materials under various oxidative environments by preparing in situ sol-gel condensation reaction. First, siloxane-encapsulated upconversion nanoparticle hybrid composite (SE-UCNP) which exhibits excellent photoluminescence (Photoluminescence) stability for over 40 days even at elevated temperature, in high humidity, and in harsh chemicals is fabricated for two-color binary micro barcode system. Second, luminescent light-emitting diode (LED) encapsulating material using a thermally curable quantum dot (QD)/siloxane hybrid (TSE-QD) color converter, which has superior long-term stability even at elevated temperature (120 $^\circ C$) , in high humidity (85 $^\circ C$ / 85 % relative humidity), and in various chemicals is fabricated, and white LED with wide color gamut (116% of NTSC) is demonstrated. Lastly, siloxane-encapsulated OIHP NP hybrid composite (SE-OIHP NP) films of which OIHP NPs and siloxane matrix are chemically hybridized in molecular scale is fabricated for improving stability of OIHP NP against heat and moisture.