Oxygen plays a key role in various industrial processes, including combustion and energy conversion, which are involved in important fields such as fuel cells, automotive engines, and gas turbines. Thus, a real-time, accurate measurement of oxygen concentration is crucial for the seamless functioning of these industries.
Unfortunately, existing oxygen concentration measurement technologies rely on contact measurements using probes, which cannot withstand high-temperature environments. Moreover, despite the availability of a few optical temperature measurement technologies, the organometallic materials they utilize degrade at temperatures above 120 °C.
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To address this problem, a team of researchers led by Prof. Kyung Chun Kim from Pusan National University, Korea, developed and tested a non-contact technique to measure oxygen concentration under high temperatures. In their study, which was made available online on 19 April 2022 and published in Volume 364 of Sensors and Actuators B: Chemical on 01 August 2022, the team described how a phosphorescent material’s glow, or “phosphorescence,” can be leveraged to measure oxygen concentration.
The material in question was yttrium oxide doped with europium (Y2O3:Eu3+)—a phosphor, i.e., a material that emits light in response to radiation—which has a highly temperature-resistant crystalline structure. Like other phosphors, Y2O3:Eu3+ absorbs light energy and re-emits it at a lower frequency. However, owing to its unique molecular arrangement with oxygen vacancies, its phosphorescence varies depending on the surrounding oxygen. This high sensitivity to oxygen makes Y2O3:Eu3+ a suitable non-contact luminescent probe.
To investigate this property further, the team set up a two-dimensional (2D) temperature and oxygen concentration adjustable furnace with a quartz window (a window that allows light to pass freely in both directions) and used it to shine an ultraviolent (UV) LED light towards a Y2O3:Eu3+ tablet. On measuring the resultant phosphorescence using a spectrometer, the team found that it was most sensitive to the oxygen concentration at a temperature beyond 450°C for a wavelength of 612 nm. Beyond 450°C, the sensitivity of Y2O3:Eu3+ to oxygen concentration increased with increasing temperature but decreased with an increase in the oxygenconcentration.