A novel ultra-thin-walled ZnO microtube cavity supporting multiple optical modes for bluish-violet photoluminescence, low-threshold ultraviolet lasing and microfluidic photodegradation

ZnO optical microcavities have shown great promise as a potential core component material/structure for ultraviolet lasers, light-emitting diodes and photonic sensors because of their outstanding optoelectronic properties. Here, we report a novel ultra-thin-walled ZnO (UTW-ZnO) microtube cavity with a wall thickness of ~750 nm, supporting multiple types of optical modes, including in-tube Fabry–Perot modes, in-wall Fabry–Perot modes and wave-guided whispering gallery modes (WG-WGMs). The free-exciton recombination rate and exciton–exciton collisions are promoted in the cavity. The intensities of near-band edge (ultravoilet (UV) light) and X-band (blue light) emission are therefore increased at least one order of magnitude in the temperature range of 0–500 °C. Meanwhile, the temperature-sensitive multicolor luminescence of the UTW-ZnO microtubes in the visible band from near-white to bluish-violet is demonstrated for the first time. Low-threshold UV lasing is also achieved in the UTW-ZnO microtube by WG-WGMs, where the excitation threshold is down to 5.50 μW. Furthermore, light harvesting in the microtube cavity is beneficial to boosting the ZnO catalytic performance for photodegradation of organic dyes. The UTW-ZnO microtube exhibits compatibility to microfluidic channels for recyclable on-chip degradation. The present work provides new opportunities to design novel tubular wide-bandgap semiconductor devices for a variety of optoelectronic applications in micro/nanophotonics. Microscale semiconductor tubes that emit ultraviolet laser light have been developed by researchers in China and the UK. Lasers employ an optical cavity that boosts light like the body of a guitar amplifies sound. The miniaturization of lasers requires smaller cavities, which can be difficult to fabricate with high precision and reproducibility. Now, Yinzhou Yan from the Beijing University of Technology and colleagues have created microscale semiconductor tubes and have demonstrated their ability to enhance optical emission. They used a method they developed – optical vapor supersaturated precipitation – to make hexagonal zinc oxide tubes that were 50 micrometers in diameter and had walls that were just 750 nanometers thick. The team showed that these structures can trap and enhance light in multiple ways, demonstrating their flexibility for optoelectronic applications. A novel ultra-thin-walled ZnO microtube cavity with a wall thickness of ~750 nm, supporting multiple types of optical modes, including in-tube Fabry–Perot modes, in-wall Fabry–Perot modes and wave-guided whispering gallery modes is fabricated via optical vapor supersaturated precipitation. The intensities of near-band edge and X-band emission are therefore increased at least one order of magnitude in the temperature range of 0–500 °C. The ultra-thin-walled ZnO microtube demonstrates unprecedented applications, for example, temperature-sensitive multicolor luminescence, low-threshold ultravoilet (UV) lasing and high-performance recyclable on-chip photodegradation, within one platform. It provides new opportunities to design multifunctional tailored wide bandgap semiconductor devices for a variety of optoelectronic applications in micro/nanophotonics.