Synthesis of Fast Curing, Water‐Resistant and Photopolymerizable Glass for Recording of Holographic Structures by One‐ and Two‐Photon Lithography

Abstract

functional materials for tackling challenging material-related problems in diverse areas such as medicine, pharmacy, mechanics, electronics, chemistry and others. [1][2][3][4][5] One of the most popular and successful applications of the hybrid sol-gel technology is the development of multifunctional coatings for the protection of metal surfaces against corrosion and environmental degradations. [6] Other promising applications include photoreactive hybrid sol-gel coatings for the fabrication of microstructured components such as optical waveguides, [7] photonic crystals [8] and microfluidic devices. [9] The main advantage of the hybrid sol-gel technology, in comparison to conventional organic or inorganic chemistries, is its flexibility which allows for a combination of both organic and inorganic functional chemistries that facilitates low temperature preparation, generally at room temperature. [5] As a result, structural properties of thermo-sensitive organic groups are maintained and remain available for further exploitation as network modifiers in the inorganic structure and in the microstructuring processes used to fabricate miniature devices. Among the many applications of the sol-gel technology, the preparation of photopolymerizable glasses for holographic applications is of particular interest. The concept of sol-gel preparation of hybrid organic-inorganic materials by the Advancements in hybrid sol-gel technology have provided a new class of holographic materials as photopolymerizable glasses. Recently, a number of photosensitive glass compositions with high dynamic range and high spatial resolution have been reported and their excellent capability for volume holography has been demonstrated. Nevertheless, challenges remain, particularly in relation to the processing time and environmental stability of these materials, that strongly affect the performance and durability of the fabricated holograms. State-of-the-art photopolymerizable glasses possess long curing times (few days) required to achieve thick films, thus limiting the industrial implementation of this technology and its commercial viability. This article presents a novel, fast curing, water-resistant, photopolymerizable hybrid sol-gel (PHSG) for holographic applications. Due to introducing an amine-based modifier that increases the condensation ability of the sol-gel network, this PHSG overcomes the problem of long curing time and can readily produce thick (up to a few hundred micrometers) layers without cracking and breaking. In addition, this PHSG exhibits excellent water-resistance, providing stable performance of holographic gratings for up to 400 h of immersion in water. This finding moves photopolymerizable glasses to the next development stage and renders the technology attractive for the mass production of holographic optical elements and their use across a wide number of outdoor applications.

Charge transfer mediated triplet excited state formation in donor–acceptor–donor BODIPY: Application for recording of holographic structures in photopolymerizable glass

“…This value is close to one previously reported for gratings with similar thickness and spatial frequency recorded in a photopolymerizable glass sensitized with Irgacure 784. 51 Thus, successful holographic recording of transmission gratings confirms comparable efficiency of both ABA- NPG and I 2 BDP -NPG photoinitiating systems for polymerisation of methacrylates in PG.…”

“…This value is close to one previously reported for gratings with similar thickness and spatial frequency recorded in a photopolymerizable glass sensitized with Irgacure 784. 51 Thus, successful holographic recording of transmission gratings confirms comparable efficiency of both ABA-NPG and I 2 BDP-NPG photoinitiating systems for polymerisation of methacrylates in PG. Among the various aspects of the holographic recording material, stability under UV-exposure is one of the key parameters required for the sustained performance of holographic optical elements and their successful implementations.…”

“…Please do not adjust margins Please do not adjust margins Holographic recording of volume phase transmission gratings was carried out using the set-up presented in Figure S29 (ESI). As was proposed in our previous work, 51 during holographic patterning of PG layers, photopolymerization is triggered in illuminated areas. Under these conditions, ABA is expected to undergo intermolecular charge transfer and form triplet excited states of BODIPY via SOCT-ISC, which further react with NPG to produce free radicals.…”

“…S29 (ESI †). As was proposed in our previous work, 51 during holographic patterning of PG layers, photopolymerization is triggered in illuminated areas. Under these conditions, ABA is expected to undergo intermolecular charge transfer and form triplet excited states of BODIPY via SOCT-ISC, which further react with NPG to produce free radicals.…”

“…Due to its higher triplet state yield, ABA was chosen as a photosensitizer component for free-radical polymerization in a holographic recording material based on a photopolymerizable glass (PG), a hybrid organic-inorganic sol-gel material. Previously reported PG 51 was sensitized by incorporation of Irgacure 784 as a photoinitiator with maximum absorption in the range of 400-480 nm. This makes the material less sensitive at 532 nm, the second harmonic of single frequency Nd:YAG lasers typically used for holographic recording.…”