Observation of Tunable Refractive Indices and Strong Intermolecular Interactions in Newly Synthesized Methylene-biphenylene-Bridged Silsesquioxane Thin Films

Abstract

A series of methylene-biphenylene-bridged silsesquioxane thin films were synthesized from 4,4′-bis(trimethoxysilylmethyl)biphenyl (MBP) and methyltrimethoxysilane (MTMS) monomers at different molar ratios. A sol−gel process employing hydrolysis and condensation reactions was used to synthesize the precursors that were then spin-coated onto a silicon wafer. Optical properties of the thin films were investigated using spectroscopic ellipsometry (SE). Refractive index values increased from 1.40 for 0 mol % MBP to 1.60 for 100 mol % MBP. These are promising results for reliable encapsulants for a high-performance white light emitting diode (LED) given its high refractive index value and absence of epoxy moieties. The dielectric functions, consisting of real and imaginary parts closely related to refractive index and extinction coefficient, were also investigated. A new peak at 3.96 eV was observed for the 75 and 100 mol % MBPs in the imaginary dielectric functions, which was absent for the 25 and 50 mol % MBPs. The main origin for the new peak was thought to be the same as that for the peak at 4.67 eV, from the pseudo B1u ← A1 g transition of the six-membered ring constituting the biphenyl group. Herein, we suggest that the peak at 3.96 eV is generated from interactions between the biphenyl rings in the silsesquioxane materials, which can be explained by the local field correction and/or the planarization models.

High refractive index thermally stable phenoxyphenyl and phenylthiophenyl silicones for light‐emitting diode applications

“…There are additional losses due to the RI mismatch between the encapsulant and the phosphor materials which are used to produce a white output spectrum. While many chemistries can achieve RIs of 1.5–1.70, which might enable 5–10% more light output, no high RI materials have met the combined conditions of high heat stability, high light flux stability, room temperature liquid dispensing, and reasonable cost that manufacturers require for HBLEDs. Methyl phenyl silicone thermosets, with a RI of 1.41–1.53, are the current industry standard and to date are the only systems which can tolerate high heat and high light flux for the anticipated 50,000 h lifetimes of a HBLED.…”

Study of thermal and optical properties of epoxy/organically modified silicate hybrids

“…As a result, the light extraction efficiency of LEDs encapsulated by silicone-modified epoxy materials is fundamentally limited. 13 Bae et al 14 prepared cycloaliphatic epoxy oligosiloxane resins with a high transmittance (∼90%) and a high refractive index of up to 1.583. Seok et al 15 prepared epoxysilane-based inorganic-organic hybrid resins with a optical transmission above 90% from 300 nm to entire visible region, and varied from 1.556 to 1.588 in refractive index at 632.8 nm.…”

Solution-processed crack-free oxide films formed using SiO2 nanoparticles and organoalkoxysiloxane precursors

“…Siloxane-based SOGs, however, contain direct organic bonds; i.e., Si-R, where R corresponds to methyl (-CH 3 ) or other organic group. The organic group inhibits the formation of cracks and provides the capability to form thick films [7,10].…”