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The well-resolved absorption, excitation, and luminescence spectra of [Ir(ppy)2bpy]+ (ppyH = 2-phenylpyridine, bpy = 2,2'-bipyridine) in different media at cryogenic temperatures are presented. In solutions and glasses at ambient temperature the lowest energy excited state corresponds to an Ir - bpy charge-transfer excitation whereas in the crystalline host lattice [Rh(ppy)2bpy]PF6 the lowest excited state at 21 450 cm-1 is assigned to a 37r-r* excitation localized on the cyclometalating ppy- ligands. The next higher excited Ir - bpy charge-transfer state has shifted to 21 820 cm-', only 300 cm-I above the 3LC excited state. The close proximity of the 3LC and 3MLCT excited states and the large spin-orbit coupling constant of Ir3+ induce a strong mixing of charge-transfer character into the 3LC lowest excited states, resulting in increased oscillator strengths, reduced lifetimes, short axis polarized transitions, and a large zero-field splitting of 10-15 cm-1

Hexagonal Sodium Yttrium Fluoride Based Green and Blue Emitting Upconversion Phosphors. -Pure hexagonal Na 3x Ln 2-x F 6 (Ln: Y, Nd, Er, Tm, Yb; x = 0.45) phosphor powder samples are synthesized from Ln2O3, Na2CO3, HBr, and HF in H2O (550-540°C, 40 h). As revealed by powder XRD the samples crystallize in the space group P63/m with Z = 1. The samples doped with 18% Yb + 2% Er and 25% Yb + 0.3% Tm show the highest upconversion efficiencies for green and blue emission, respectively. The obtained phosphor materials show no degradation under high-power IR laser excitation. -(KRAEMER*, K. W.; BINER, D.; FREI, G.; GUEDEL, H. U.; HEHLEN, M. P.; LUETHI, S. R.; Chem. Mater. 16 (2004) 7, 1244-1251; Inst. Chem. Biochem., Univ. Bern, CH-3012 Bern, Switz.; Eng.) -W. Pewestorf 26-017

Luminescence D 6540Highly Efficient Multicolor Upconversion Emission in Transparent Colloids of Lanthanide-Doped NaYF4 Nanocrystals. -Transparent colloidal solutions of Yb/Er and Yb/Tm doped NaYF4 nanocrystals exhibit bright upconversion emission in the red, green, and blue spectral region by excitation around 1 µm with a laser of moderate power. These new systems show a substantial improvement on the order of 10 8 compared to previously reported systems. -(HEER, S.; KOEMPE, K.; GUEDEL, H.-U.; HAASE*, M.; Adv.

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