A new blue-green phosphor, Ca 6 BaP 4 O 17 :Ce 3+ , which can be prepared by conventional solid-state synthesis, is reported as a candidate phosphor for solid-state lighting with near-ultraviolet LEDs. Under excitation at around 400 nm, Ca 6 BaP 4 O 17 :Ce 3+ shows strong blue-green emission with the peak position at 477 nm. Ce 3+ ,Si 4+ co-doping is found to enhance the luminous intensity, and the unique emission characteristics of this combination are studied and related to the crystal structure. Ca 6 BaP 4 O 17 is an exceptional host material, which also accommodates Eu 2+ , emitting strong yellow light under 400 nm excitation. A fabricated white LED, combining Ca 6 BaP 4 O 17 :Ce 3+ ,Si 4+ with Ca 6 BaP 4 O 17 :Eu 2+ and a red CaAlSiN 3 :Eu 2+ phosphor, achieved a luminous efficacy of 45 lm W À1 with a color-rendering index of 93 around the correlated color temperature of 4500 K.

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The deep red phosphor Sr 4 (PO 4 ) 2 O:Eu 2+ , which has an excitation peak around 450 nm for blue LED applications, is reported. This behavior is unusual for most phosphate phosphors. The crystal structure of Sr 4 (PO 4 ) 2 O:Eu 2+ is found to be monoclinic P2 1 and isotypic with Ca 4 (PO 4 ) 2 O:Eu 2+ , which also shows deep red emission. Sr 4 (PO 4 ) 2 O:Eu 2+ has a larger lattice volume than Ca 4 (PO 4 ) 2 O:Eu 2+ , but their emission and excitation spectra at room temperature are very similar. The key factors are discussed for achieving a large redshift of the 5d levels of Eu 2+ ion in order to emit red light. In particular, the importance of the anion polarizability and the distortions of the metal coordination polyhedra are discussed, including the effective coordination number. Importantly, Sr 4 (PO 4 ) 2 O:Eu 2+ lacks the yellow emission at 77 K, which is found in Ca 4 (PO 4 ) 2 O:Eu 2+ . The differences in thermal quenching behavior for Eu 2+ dopants in Sr 4 (PO 4 ) 2 O:Eu 2+ and Ca 4 (PO 4 ) 2 O:Eu 2+ are attributed to the degree of auto/photo-ionization due to differences in the band gaps of these compounds. The importance of the large band gap of the host lattice in avoiding non-radiative processes of energy relaxation was confirmed.