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Upconversion luminescence of Er3+ in the chloride glass system has been investigated in ZnCl2-BaCl2-KCl-ErCl3 and CdCl2-BaCl2-KCl-ErCl3 glasses. Under 800 nm excitation, the glasses gave upconversion luminescence with barely detectable red (around 660 nm), very intense green (around 525–560 nm), and considerably intense blue (around 410 nm) emissions. The intensity of blue emissions was far stronger than that observed for any of other Er3+-doped glass systems, revealing that Er3+-doped chloride glasses can efficiently convert the infrared light into much shorter wavelengths. The green emission is attributed not only to the thermally coupled 2H11/2 and 4S3/2→4I15/2 transition but also to the 2H9/2→4I13/2 transition. The blue emission is due to the 2H9/2→4I15/2 transition. The blue and green upconversion luminescence results from a two-photon process.

As previously reported, a selectively strong green emission due to the Ho3+: (5F4, 5S2)→5I8 transitions is observed in Nd3+–Ho3+ co-doped ZrF4-based fluoride glasses under 800 nm excitation. As an attempt to more enhance Ho3+ up-conversion luminescences in the Nd3+–Ho3+ co-doped ZrF4-based glasses, Yb3+ ions were added to the glasses. As a result it was found that, in 800 nm excitation of 60ZrF4⋅30BaF2⋅(8−x)LaF3⋅1NdF3⋅xYbF3⋅1HoF3 glasses (x=0 to 7), sensitized up-conversion luminescences are observed at around 490 nm (blue), 545 nm (green), and 650 nm (red), which correspond to the Ho3+: F35→5I8, (5F4, 5S2)→5I8, and F55→5I8 transitions, respectively. The intensities of the green and red emissions in a 3 mol % YbF3-containing glass were about 50 times stronger than those in no YbF3-containing glass. This is based on sensitization due to Yb3+ ions. In particular, the green emission is extremely strong so that the Nd3+–Yb3+ –Ho3+ co-doped ZrF4-based glasses have a high possibility of realizing a green up-conversion laser glass. Up-conversion processes for the blue, green, and red emissions were two-photon processes assisted by Nd3+→Yb3+→Ho3+ energy transfer. The up-conversion mechanism in the glasses is discussed.

Optical absorption and extended X-ray absorption fine structure (EXAFS) spectra were measured on series of ZrF4−BaF2−LaF3, ZrF4−BaF2−MF−LaF3 (M; Li, Na, K, Rb, or Cs) and AlF3−BaF2−CaF2−YF3 glasses doped with Ni2+. The optical absorption spectra show that Ni2+ ions in all the glasses exist in octahedral coordination sites with six F- ions. The values of ligand field strength, 10Dq, were obtained from the optical absorption spectra, and Ni−F interatomic distances, r Ni-F, were determined by EXAFS analyses. The linear relationship between 10Dq and r Ni-F is found and interpreted by simple ligand field theory. The compositional dependence of the 10Dq and r Ni-F is discussed in terms of the basicity of glasses. We discuss the optical property and the local environment of Ni2+ in the fluoride glasses in comparison with those of oxide glasses.