B–O–O–B Impurity Induces Ultralong Room-Temperature Phosphorescence of Boric Acid
Yiting Song, Xiujuan Duan, Yanan Jiang, Yuchen Ma
Abstract
Organic materials that can emit ultralong room-temperature phosphorescence (RTP) have attracted a great deal of interest. Whether the pure boric acid (BA) solid can emit RTP and the origin of the RTP in BA caused a debate recently. Herein, our first-principles calculations and experimental measurements suggest that RTP of BA originates from the B–O–O–B group in a (H 2 BO 3 ) 2 species, which can be formed by polymerization of two dehydrogenated BA molecules under light irradiation. The calculated absorption, fluorescence, and phosphorescence spectra of B–O–O–B match well with the experiments. Experimental X-ray photoelectron and X-ray absorption spectra evidence the existence of B–O–O–B in BA. The O–O bond in B–O–O–B can break upon optical excitation, creating two B–O radicals. Radiative transition from localized dangling orbitals of the B–O radicals to the delocalized orbitals of the crystal bulk leads to the observed RTP. Our calculated phosphorescence lifetime is ∼1 s, which agrees well with the experiment.