Optical properties of Bi3+ ions doped in NaYF4

Photoluminescence and photoexcitation spectra of Bi3+ ions doped in NaYF4 crystals have been examined in UV and VUV regions. A broad luminescence band has been observed at 2.82 eV under photoexcitation of UV and VUV light. The photoexcitation spectrum of this luminescence exhibits several structures at 4.0–5.2 eV and 5.6–7.3 eV. These excitation bands are due to intra-ionic transitions in Bi3+ ions, probably corresponding to so-called A band (1S0→3P1 transitions) and C band (1S0→1P1 transitions), respectively. The optical process and the relaxed excited states of Bi3+ ions are discussed on the basis of s2→sp electronic transition in Bi3+ ion whose site has a low symmetry in NaYF4 host lattices.