Enhanced near-infrared emission of Er3+as a synergistic effect of energy transfers in Bi3TeBO9:Yb3+/Er3+phosphors

Enhanced near-infrared emission at 1531 nm of Er3+ ions excited by Bi3+ and/or Yb3+ ions was revealed in Bi3TeBO9:Yb3+/Er3+ phosphors. The microcrystalline powders investigated: Bi3TeBO9:Er3+, Bi3TeBO9:Yb3+ and Bi3TeBO9:Yb3+/Er3+ were synthesized by means of the modified Pechini method. Their hexagonal structure with P63 space group was confirmed by XRD measurements. The morphology of the above-mentioned samples was analyzed using SEM technique. The results of mu-Raman investigations showed low phonon energy of Bi3TeBO9 matrix. The characteristic Er3+ emission at 1531 nm assigned to the 4I13/2 -> 4I15/2 transition in Bi3TeBO9:Er3+ and Bi3TeBO9:Yb3+/Er3+ powders was excited by Bi3+ or Yb3+ ions (the 1S0 -> 3P1 or 2F7/2 -> 2F5/2 transitions) upon their excitation at 327 or 975 nm, respectively. It was revealed that the effective energy transfer from the excited Bi3+ ions (at 327 nm) directly to Er3+ ions or indirectly to Er3+ ions both via the excitation of Bi3+ ions in VIS range or excitation of Yb3+ ions in the NIR range results in synergistic effect, which produces enhanced emission at 1531 nm of Er3+ ions in Bi3TeBO9:Yb3+/Er3+ system. Moreover, it was found that the effective energy transfer from the excited Yb3+ ions (at 975 nm) directly to Er3+ ions results in the efficient emission at 1531 nm of Er3+ ions. Furthermore, the calculations of energy transfer efficiency and quantum efficiency proved the effective energy transfer from Bi3+ to Yb3+ and from Yb3+ to Er3+ ions. The corresponding mechanisms of energy transfer processes in the investigated materials were discussed on the basis of reflectance, excitation and emission spectra and measured decay times. The results indicate a potential of the use of Bi3TeBO9:Yb3+/Er3+ powders as spectral converters in new generation of photovoltaic devices.