A simple approach to fabricating optical microcavities, developed at the University of Turku, will enable more researchers to engage in the light-matter studies that are critical to the development of quantum optics, next-generation displays, ultra-efficient lasers, and other emerging technologies. The all-solution-processed method uses coating techniques to fabricate optical microcavities for studying polaritons (hybrid particles made from light and matter) without the need for expensive, vacuum-based technologies. The new fabrication process has the potential to significantly reduce costs while maintaining, or even exceeding, the performance of conventional methods. “Our approach makes it a lot easier to study strong light-matter interactions, because we offer a method that is simple, cheap, and far less energy-intensive than existing methods,” professor Konstantinos Daskalakis said. “We have eliminated the need for vacuum-based techniques without compromising performance, and that makes strong light-matter interaction studies more accessible to the researchers.” A laser beam interacting with polariton microcavities, revealing how polaritons help protect emitting materials from brightness loss. Courtesy of University of Turku/Mikael Nyberg. The solution-processed, dielectric microcavities incorporate Rhodamine 6G (R6G) films in a poly(vinyl alcohol) matrix as the active material. The researchers used spin-coating and an automated dip-coating process to fabricate the microcavities, and optimized them to prevent interlayer mixing and maintain the integrity of the active layers. The microcavities demonstrated a Rabi splitting of more than 400 mega-electron volts (MeV) and photoluminescence with uniform dispersion along the lower polariton mode. The researchers also investigated polariton light emission. The ability to directly measure the light emitted from polaritons provided insight into polariton dynamics and enabled the researchers to observe the effects of polaritons suppressing bimolecular annihilation in organic emitters — a process that reduces the efficiency of light emission and contributes to long-term material degradation. “Being able to measure light coming from polaritons made it possible for us to see how the presence of polaritons reduces emission bleaching,” researcher Hassan Ali Qureshi said. “This is a critical step in understanding and improving the performance of polaritonic devices.” Reflectivity and photoluminescence measurements confirmed the pristine quality of the polariton microcavity samples, which achieved coupling strengths that not only matched, but in some instances surpassed those of metallic-clad microcavities. This accessible, energy-efficient approach to fabricating polariton microcavities and observing polariton dynamics could expand the potential for research into light-matter interactions significantly. By combining a simple fabrication approach for polariton microcavities with accessible optical characterization techniques, this work could lower the barriers to exploring polariton physics. Solution-based fabrication techniques for advancing polaritonic devices could also open new possibilities for studying sensitive organic materials and developing more stable, efficient light-emitting technologies. The research was published in Advanced Optical Materials (www.doi.org/10.1002/adom.202500155).