Near-infrared Broadband Luminescence Properties of Bi and Nd Co-doped CsI Crystals

Bi and Nd co-doped CsI (Bi,Nd:CsI) crystals were grown by a vertical Bridgman method. The result by X-ray diffraction shows that the as-grown Bi,Nd:CsI crystal exhibits a single-phase (Pm3m) CsI, and the doping of Bi and Nd ions into the Bi,Nd:CsI crystal lattice does not affect its basic crystal structure. It was found that the co-doping could lead to the decrease of Bi doping concentration. The co-doped crystal was annealed, and the absorption and emission spectra of the crystal were determined. The results show that Bi and Nd co-doping can increase the concentration of V′_cs. A high temperature annealing can obtain a lower valence state of the Bi ions luminous clusters, which improves the near-infrared broadband luminescence properties of the crystal. The Bi,Nd:CsI crystal has two Raman characteristic peaks of near-infrared broadband luminescence centers, which are located at 164 and 176 cm^-1, respectively. In addition, the formation of Bi₊ and Bi₂₊ bound up with the aggregation of high-valence Bi ions was also discussed.