Effect of phosphor geometry on the luminous efficiency of high-power white light-emitting diodes with excellent color rendering property

Abstract

High-power white light-emitting diodes (LEDs) are fabricated by combining blue LEDs and green (Ba,Sr)(2)SiO(4):Eu(2+) and red CaAlSiN(3):Eu(2+) phosphors with varying phosphor geometry. The white LED having separated the phosphor layer by the silicone gel layer between green and red phosphor layers shows. superior optical properties. The luminous efficiency (eta(L)) is improved by a decrease of reabsorption of green light by red phosphor owing to a difference among refractive indices. The white LED shows very high eta(L) of 51 lm/W and a high color rendering index of 95 under 350 mA. In addition, improved luminous properties of the white LED including a separated phosphor layer are confirmed via ray-trace simulation. (C) 2008 Optical Society of America.