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Maak, Christian; Strobel, Philipp; Weiler, Volker; Schmidt, Peter J.; Schnick, Wolfgang (2018): Unprecedented Deep-Red Ce3+ Luminescence of the Nitridolithosilicates Li38.7RE3.3Ca5.7[Li2Si30N59]O2F (RE = La, Ce, Y). In: Chemistry of Materials, Vol. 30, No. 15: pp. 5500-5506
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Abstract

Ce3+ doped solids find broad application, e.g. in phosphor converted light emitting diodes, utilizing the usually broad blue to yellow-orange emission of the respective phosphors. The red to infrared spectral range was not yet accessible with the activator Ce3+, even in nitride host materials. Here, we report on the nitridolithosilicates Li38.7RE3.3Ca5.7[Li2Si30N59]O2F (RE = La, Ce, Y) with unique, red-shifted Ce3+ luminescence. The materials were synthesized by solid-state metathesis reactions in tantalum ampules. The isotypic crystal structures exhibit a highly condensed three-dimensional network made up of SiN4 and LiN4 tetrahedra. Crystal structures were refined from single-crystal and powder X-ray diffraction data. The results are supported by energy-dispersive X-ray spectroscopy as well as charge distribution, lattice energy, and bond valence sum calculations. Optical band gaps of approximate to 4 eV were determined from diffuse reflectance UV/vis data using Tauc plots. The nitridolithosilicates are highly excitable from the UV to the green-yellow spectral range with a preferred excitation wavelength of lambda(exc) approximate to 540 nm. The emission spectra peak is in the deep-red with lambda(em) = 638-651 nm (fwhm approximate to 3600 cm(-1)). According to the unique absorption and emission properties, application as luminescent solar concentrators or in horticultural lighting appears promising.