Fluorescent dyes of a new generation
A research team at Empa and ETH Zurich has developed single crystals made of lead halide perovskites, which are able to gage radioactive radiation with high precision. Initial experiments have shown that these crystals, which can be manufactured from aqueous solutions or low-priced solvents, work just as well as conventional cadmium telluride semi-conductors, which are considerably more complicated to produce. The discovery could slash the price of many radio-detectors – such as in scanners in the security sector, portable dosimeters in power stations and measuring devices in medical diagnostics
Lead halide perovskite crystals not only can detect radiation but can also serve as a novel class of brightly fluorescent “inorganic pigments”. In 2015 Maksym Kovalenko’s Team discovered that colloidal lead halide perovskite nanocrystals emit bright light in the entire visible spectral range and are stable in ambient air. Most importantly and contrary to nearly all conventional quantum dots, these novel phosphors do not require laborious encapsulation into other matrices for bringing about their bright luminescence.
In their latest paper, recently published in “Nano Letters”, they describe how to prepare such nanocrystals in an easy way. They drenched mesoporous silica with a perovskite precursor solution and simply dried out the solvent. The nanocrystals – formed and encapsulated in the silica matrix – exhibit a very bright photoluminescence, both with visible light and under UV radiation. The color of these “inorganic dyes” can be tuned by both quantum size effects as well as by the chemical composition of the crystals. Also exhibiting intrinsic haze due to scattering within the composite, such materials may find applications as replacements for conventional phosphors in liquid-crystal display technologies in future flat-screen TV’s.