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.
Low-temperature luminescence and absorption spectra were recorded of VClz doped into MgCl, and CdCl, as well as of the pure compound. There is evidence for excitation energy transfer in Velz down to 5 K. In the diluted materials the luminescence remains unquenched up to 200 K (Cd,,V,Cl2) and 250 K (MgI-,V,CI2). The broad-band 4T2, - 4Azs luminescence transition is highly structured in the diluted samples. There is multiple evidence for a Jahn-Teller effect in the 4Tz, state with an estimated Jahn-Teller energy of the order of 200 cm-I. Polarized absorption and Zeeman meausurements were used to assign the 4Az, -,E,, *TI, transitions.