Evaluating the use of blue phosphors in white LEDs: the case of Sr0.25Ba0.75Si2O2N2:Eu2+

Abstract

The luminescence properties of the blue emitting phosphor Sr 0.25 Ba 0.75 Si 2 O 2 N 2 :Eu 2+ are extensively investigated. This oxonitridosilicate phosphor features strong 4f 6 5d 1 - 4f 7 luminescence originating from the Eu 2+ ion, with a narrow emission band peaking at 467 nm and a full width at half maximum of only 41 nm. Thermal quenching of the blue luminescence only sets in above 450 K, making this material an interesting candidate as LED conversion phosphor. The fast decay of the luminescence prevents the phosphor to be susceptible to saturation effects at high excitation fluxes. Furthermore it is proven to be chemically stable against moisture. The only drawback is the relatively low quantum efficiency of the synthesized powder, provisionally preventing this material to be used in applications. In addition, the phosphor features a weak yellow emission band, originating from small domains featuring a different crystal structure. It is shown that the majority of the powder grains only exhibit blue emission. Finally, the spectrum of a white LED, based on a UV pumping LED and three (oxy)nitride phosphors is simulated in order to assess the usefulness of blue phosphors in LEDs for lighting. Only a marginal improvement in terms of color quality can be achieved with a narrow banded phosphor, at the expense of a decrease in luminous efficacy and overall electrical to optical power efficiency. PACS 70 – Condensed Matter: Electronic structure, Electrical, Magnetic, and Optical PropertiesPACS 42.70.-a Optical materials