Yasuo Shimomura

Synthesis, structure and optical properties of cerium-doped calcium barium phosphate – a novel blue-green phosphor for solid-state lighting

A new blue-green phosphor, Ca6BaP4O17:Ce3+, 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, Ca6BaP4O17:Ce3+ shows strong blue-green emission with the peak position at 477 nm. Ce3+,Si4+ 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. Ca6BaP4O17 is an exceptional host material, which also accommodates Eu2+, emitting strong yellow light under 400 nm excitation. A fabricated white LED, combining Ca6BaP4O17:Ce3+,Si4+ with Ca6BaP4O17:Eu2+ and a red CaAlSiN3:Eu2+ phosphor, achieved a luminous efficacy of 45 lm W−1 with a color-rendering index of 93 around the correlated color temperature of 4500 K.

Synthesis, structure and optical properties of europium doped calcium barium phosphate – a novel phosphor for solid-state lighting

A new phase, Ca6BaP4O17, was found in the CaO–BaO–P2O5 phase diagram and its Eu2+-doped derivative was evaluated as a possible phosphor for solid-state lighting. Ca6BaP4O17 was prepared by conventional solid-state synthesis and its structure was solved ab initio from high-resolution, synchrotron X-ray powder diffraction data. The bandgap of Ca6BaP4O17 was estimated to be 5.79 eV. Under excitation with UV to blue light, Ca6BaP4O17:Eu2+ shows strong yellow emission with the peak position at 553 nm. A white LED, which was fabricated with an InGaN blue chip and Ca6BaP4O17:Eu2+, achieved a luminous efficacy of 31 lm W−1 with a color-rendering index of 78 around the correlated color temperature of 6500 K.

Influence of x-ray irradiation on doped europium in BaMgAl10O17 studied by x-ray absorption fine structure and x-ray diffraction

— We studied the influence of x-ray irradiation on the doped europium ion in BaMgAl10O17 (BAM) by x-ray absorption fine structure measurement and x-ray diffraction. We found that x-ray irradiation promoted oxidation of doped europium and fading emissions. However, no difference was found in x-ray diffraction patterns before and after x-ray irradiation. We concluded that the fading of BAM after x-ray irradiation was mainly caused by oxidation of the doped europium in the BAM.