Ultra-sharp-Line Emission in Isotopic c-10BP

Abstract

Cubic boride crystals with pure boron isotopes have attracted great attention in recent years. Here, high-quality cubic boron phosphide single crystals with isotopic 10B and a maximum width reaching 1.5 mm are grown via the high-temperature molten salt method. An interesting phenomenon that there are many discrete sharp lines in the low-temperature (4–80 K) photoluminescence spectra is observed. Besides, as temperature increases, the luminescence intensity of these sharp lines shows a nonmonotonic decay with two different trends exhibited. Based on analyses, the sharp-line emission originates from phonon-assisted donor–acceptor pair radiative recombination. The nonmonotonic decay is affected by the number of assisting phonons and the degree of thermal ionization under the effect of temperature, and the different decay trends are attributed to the effect of thermal ionization dependent on the distance between the donor and acceptor. Results obtained in this research are expected to enrich the knowledge concerning cubic boride crystals in the aspect of physical properties.