Digital Luminescence Patterning via Inkjet Printing of a Photoacid Catalysed Organic-Inorganic Hybrid Formulation

Abstract

Accurate positioning of luminescent materials at the microscale is essential for the further development of diverse application fields including optoelectronics, energy, biotechnology and anti-counterfeiting. In this respect, inkjet printing has recently attracted great interest due to its ability to precisely deposit with high throughput and no contact, functional materials on different types of substrates. Here, we present a novel photoacid catalysed organic-inorganic hybrid luminescent ink. The formulation, containing monomers bearing epoxy and silane functionalities, a photoacid generator and a small percentage of Rhodamine-B, shows good jetting properties and adequate wetting of the deposited droplets on the receiving substrates. Ultraviolet exposure of the deposited material triggers the cationic ring-opening polymerization reaction of the epoxy groups. Concomitantly, if atmospheric water is available, hydrolysis and condensation takes place, overall leading to a luminescent crosslinked hybrid organic-inorganic polymeric material obtained through a simple one-step curing process, without post baking steps. Advantageously, protection of the ink from actinic light delays the hydrolysis and condensation conferring long-term stability to the ink. Digital patterning leads to patterned emissive surfaces and elements with good adhesion to different substrates, mechanical and optical properties for the fabrication of optical and photonic elements and devices.

Optical Planar Waveguide Sensor with Integrated Digitally-Printed Light Coupling-in and Readout Elements

“…Printing of these continuous areas was achieved with our printer by using 2880 dpi in the substrate moving direction, while keeping 185 dpi in the perpendicular direction. These printing conditions resulted in drop coalescence leading to continuous features in the substrate, as previously described elsewhere [38]. Besides the luminescent light coupling-in element, we incorporated a second inkjet-printed luminescent layer (HRI-RhodB-02) on the other side of the planar waveguide sensor structure.…”

“…UV ozone treatment was performed on a UV ozone reactor UVO 342 (Jelight company Inc., Irvine, CA, USA) to remove any contamination in the glass substrates, leaving silanol groups exposed on the surface [38]. As a result, important changes in the wettability and in the adhesion were obtained [24].…”

“…The movement of the substrate while printing was at a constant speed of 20 mm/s by using an eTrack linear stage from Newmark systems Inc. (Mission Viejo, CA, USA) commanded by IMS-Terminal software (Marlborough, MO, USA). The printhead was mounted in a metallic block, provided with a heater and thermocouple connected to a temperature control unit that fixed the printhead temperature at the set point (32 °C) [24,38].…”

“…The curing process was carried out under mild vacuum conditions placing the printed samples inside a chamber with an optical access. A vacuum of 100 mBar was attained inside the chamber by using a vacuum pump [38]. To reduce the evaporation of the components of the ink while the vacuum reach the desired pressure, UV exposure was immediately activated once this pressure level was reached.…”

“…Temperature readout can be carried out by measuring the luminescence intensity of this element. For the implementation of the two luminescent functional layers, we make use of our recently-developed inkjet printing platform based on photoacid-catalyzed organic-inorganic hybrid formulations including light-emissive molecules [24,38]. Inkjet printing, enabling the digital deposition of materials, has been demonstrated to be a powerful tool for the preparation and integration of functional elements and devices in a flat geometry [25,39,40,41,42,43,44,45,46].…”