A highly emissive broadband phosphor based on B₂O₃/SiO₂ nanoparticles was prepared using a sol–gel method. The room temperature phosphorescence (RTP) produced from this phosphor was carefully studied and its phosphorescence spectra were found to be featured with two peaks in the visible region. One of the peaks at 540 nm originated from B₂O₃ and the other at 470 nm was generated from SiO₂. The B₂O₃/SiO₂ nanoparticles are noncytotoxic and possess remarkable environmental stability. Therefore, the B₂O₃/SiO₂ phosphors can serve as bioprobes for cellular imaging.