Thanks to new technological advancements, materials with cross-luminescence are getting new attention after a long period of reduced research activity. Users at FinEstBeAMS from University of Tartu work at gaining new knowledge on cross-luminescent compounds.
Scintillators are compounds capable of emitting light when excited by an ionizing radiation, such as X- and gamma-rays or high energy particles. These materials are widely employed in many fields, from high-energy physics to Positron Emission Tomography (PET) for medical functional imaging. Cross-luminescence is a property peculiar of some scintillators, where the light emission is extremely fast namely, in the nanosecond domain. Mastering and employing these fast-emitting compounds can bring significant advancements in applications such as cancer diagnosis, where high time-resolution increases the quality of the diagnostics.
This is why Marco Kirm, professor in Experimental Physics at University of Tartu, Estonia, and his team came to MAX IV in November and spent one week performing experiments on materials with cross-luminescence at FinEstBeAMS, the Estonian-Finnish beamline. The team used the advanced time-resolved spectroscopy techniques available at FinEstBeAMS, which were implemented in October by the team from the University of Tartu. They performed a thorough analysis on a set of powder and crystalline samples of cross-luminescent ternary and binary fluorides to understand their electronic structure, electronic excitation, and spectral and timing characteristics.
“Cross-luminescence was first observed in the 1980s in binary compounds”, says professor Kirm. “Despite having a great potential due to their fast emission, these compounds turned out to be not well suited for practical applications”. Detection of cross-luminescent emission in binary compounds requires extreme conditions, specifically VUV (vacuum UV), and expensive detectors. “Further studies in the early 1990s showed that by using more complex compounds (formed by three or more elements), one could ‘push’ the cross-luminescence emission to the longer wavelength in the UV spectrum, which makes the detection easier”. Still, the detection of cross-luminescence resulted too complex and expensive for many practical applications, and the study of cross-luminescence lost traction.
Sometimes, advancement in a specific field of research comes in waves. And now cross-luminescent scintillators are back under the spotlight. “In the last two decades, technology of detectors for commercial use has developed. New, ultra-fast silicon photomultipliers detectors with enhanced sensitivity towards UV have become available at expenses compatible with a wide range of applications”, continues professor Kirm. Ternary or more complex cross-luminescent compounds are now promising candidates for practical applications. But before implementation, scientists must understand the governing processes for achieving cross-luminescence emission at longer wavelength and control its efficiency. “With the new detector technologies available, it is now time to go back and study these complex compounds, to understand how cross-luminescence can help improving applications such as advanced cancer diagnosis”.
Professor Kirm and his team are due to come back in early 2020 for further experiments. They are convinced that the knowledge they are gaining will encourage further studies and trigger a positive momentum. “We are now generating the basic knowledge necessary to pin-point how to improve cross-luminescence scintillators performance. Our project will open the way to further research efforts directly aimed at implementing these compounds in practical applications”.
Other scintillator materials show ultra-fast emission even without being capable of cross-luminescence. At FinEstBeAMS, Professor Kirm and his team performed also spectroscopic studies on candidate materials selected on the base of their band structure calculations. “If the properties of these candidates are promising, we hope to come back and perform further experiments at other beamlines such as FemtoMAX for more advanced time-resolved studies”.
Header image: different samples of scintillating materials tested by Kirm and his team at FinEstBeAMS.
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