The efficiency of the 1.5 μm emission associated with the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ions of a series of Er³⁺ and Yb³⁺/Er³⁺-doped Bi₂ZnOB₂O₆ microcrystalline powders was investigated.

An efficient near-infrared quantum cutting process by cooperative down-conversion of active Bi³⁺ and Nd³⁺ ions was demonstrated in Bi₃TeBO₉:Nd³⁺ phosphors. In particular, the near-infrared emission of Nd³⁺ ions enhanced by Bi³⁺ ions of a series of novel Bi₃TeBO₉:Nd³⁺ microcrystalline powders doped with Nd³⁺ ions in various concentrations was investigated. In order to investigate the luminescent properties of BTBO:Nd³⁺ powders, the excitation and emission spectra and the fluorescence decay time were measured and analyzed. In particular, the emission of Bi₃TeBO₉:Nd³⁺ at 890 and 1064 nm was excited at 327 nm (via energy transfer from Bi³⁺ ions) and at 586.4 nm (directly by Nd³⁺ ions). The highest intensity emission bands in near-infrared were detected in the spectra of Bi₃TeBO₉:Nd³⁺ doped with 5.0 and 0.5 at.% of Nd³⁺ ions upon excitation in ultraviolet and visible spectral range, respectively. The fluorescence decay lifetime monitored at 1064 nm for Bi₃TeBO₉:Nd³⁺ powders shows the single- or double-exponential character depending on the concentrations of Nd³⁺ ions. The possible mechanisms of energy relaxation after excitation Bi₃TeBO₉:Nd³⁺ powders in ultraviolet or visible spectral range were discussed. The investigated Bi₃TeBO₉:Nd³⁺ phosphors efficiently concentrate the ultraviolet/visible radiation in the near-infrared spectral range and can be potentially used as effective spectral converters. Graphical