Optical characteristics of xSrO·yAl₂O₃: Eu phosphors excited by ultraviolet light emitting diodes

Abstract

We investigated the optical characteristics of strontium aluminate phosphors excited by near ultraviolet light emitting diodes (UV LEDs). For UV LEDs applications, strontium aluminates doped with europium were prepared at high temperature in a weakly reductive atmosphere. The effect of boric acid as a flux was considered. The excitation and emission spectra of these phosphors indicated that all of them have a broad band and that the main emission peaks, situated at around 490 nm for 4SrO·7Al₂O₃ : Eu and 520 nm for SrOAl₂O₃ : Eu, are both due to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺. The typical brightness of a phosphor-converted LED, which was made with synthesized phosphors and a blue LED, was 712 mcd. By using the synthesized phosphors, phosphor-converted white LEDs could be well fabricated with good optical characteristics. In this case, color coordinates could be controlled from x = 0.1373 and y = 0.4635 to x = 0.2386 and y = 0.6066 at 20 mA and 3.69 V.