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