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The luminous efficacy of Ce:Y3Al5O12 (YAG) glass-ceramic (GC) phosphor increased with the increasing crystal size of precipitated Ce:YAG, while the light scattering coefficient decreased. This increase in luminous efficacy can be attributed to the decrease in light scattering loss owing to the decrease in light scattering coefficient with increasing Ce:YAG crystal size. According to Mie scattering theory, the reason for the decrease in the light scattering coefficient is the decrease in light scattering cross-section per unit volume with increasing Ce:YAG crystal size.

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We report the synthesis and structure of iridium(I) complexes with N,N 0 -disubstituted perimidine carbene ligands and halides or carboxylate ligands. Iodo-, chloro-, and acetate-Ir(carbene)(cod) complexes were selectively prepared by changing the bases and silver salts. Intramolecular C-H bond activation to prepare a cyclometalated Ir(III) complex, (C ∧ C:) 2 Ir(OAc) (6), where C ∧ C: is a cyclometalated perimidine carbene ligand, was achieved using a carboxylate-ligated iridium complex; otherwise, C-H activation did not proceed. Acetate-Ir(carbene)(cod) (3c) reacted with benzoic anhydride at room temperature to afford benzoate-Ir(carbene)(cod) (3d). A perimidine-carbene-and phenylpyridine-ligated Ir(III) complex, (C ∧ C:)(C ∧ N)Ir(OCOR) (8), where C ∧ N is a cyclometalated phenylpyridine ligand, was isolated in good yield by mixing 3c or 3d and phenylpyridine under reflux in toluene. On the basis of the formation of 1,3-cyclooctadiene from the reaction mixture, we propose the following reaction mechanism for the intramolecular C-H activation: carboxylate-induced C-H bond activation and subsequent pyridine-or carbene-directed C-H bond oxidative addition, followed by the isomerization of 1,5-cyclooctadiene and reaction with carboxylic acid produces (C ∧ C:)(N ∧ C:)Ir(OCOPh). The cyclometalated complex 6 reacts with sodium acetylacetonate to form (C ∧ C:) 2 Ir(acac) (11), which exhibits phosphorescent emission at λ max = 555 nm (τ = 0.65 μs, Φ PL = 0.0018) in CH 2 Cl 2 solution at room temperature.

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