Yu-Ho Won

Tunable full-color-emitting La0.827Al11.9O19.09:Eu2+,Mn2+ phosphor for application to warm white-light-emitting diodes

La0.827Al11.9O19.09:Eu2+,Mn2+ showed three emission bands when excited by ultraviolet light. A blue emission originates from Eu2+, whereas both green and red emissions originate from Mn2+. The luminescent mechanism is explained invoking the energy transfer of Eu2+→Mn2+ and Mn2+(tetrahedralsite)→Mn2+(octahedralsite). This energy transfer was confirmed by faster decay times of the blue and green emissions as energy donors. The emitted color of La0.827Al11.9O19.09:Eu2+,Mn2+ can be easily tailored from blue to red through variations of the Mn2+ content. The white-light-emitting diode fabricated via a combination of an ultraviolet light-emitting diode (λpeak=385nm) with La0.827Al11.9O19.09:Eu2+,Mn2+ showed a warm white light (Tc=3559K).

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

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.

Emission Band Change of ( Sr1 − x M x ) 3SiO5 : Eu2 + ( M = Ca , Ba ) Phosphor for White Light Sources Using Blue/Near-Ultraviolet LEDs

The luminescence properties of orange-yellow-emitting Eu 2+ -activated Sr 3 SiO 5 were optimized for application to blue/near ultra- violet (n-UV) light-emitting diodes (LEDs). Sr 2.97 SiO 5 :Eu 2+ 0.03 showed strong orange-yellow emission peaking at ∼580 nm under blue and n-UV light of 450 and 405 nm, respectively, and the effects of Ca and Ba substitutions into Sr 2+ sites on the emission band change were investigated. For the substitution of Ca, Ca 3 SiO 5 :Eu 2+ showed no orange-yellow emission under blue light due to the different crystal structures of Ca 3 SiO 5 (monoclinic) and Sr 3 SiO 5 (tetragonal). The redshift and blueshift of the emission band of (Sr 1-x Ba x ) 3 SiO 5 :Eu 2+ were explained by the competition between crystal field effect and Nephelauxetic effect. The 460 nm-emitting blue LED-pumped white LED with Sr 3 SiO 5 :Eu 2+ or a mixture of Sr 3 SiO 5 :Eu 2+ and green phosphor (Ba 2 SiO 4 :Eu 2+ ) were fabricated and they showed color coordinates of (0.343, 0.281) and (0.349, 0.339), respectively.

Red-Emitting LiLa2O2BO3 : Sm3 + , Eu3 + Phosphor for Near-Ultraviolet Light-Emitting Diodes-Based Solid-State Lighting

A red-emitting LiLa 2 O 2 BO 3 :Sm 3+ ,Eu 3+ phosphor has been synthesized and characterized optically for white light-emitting diodes (LEDs). Because the oxyborate group (O 2 BO -7 3 ) can contain high Eu 3+ concentration without concentration quenching, LiLa 2 O 2 BO 3 is a suitable host material for red-emitting phosphor for near-ultraviolet (n-UV) LEDs. When LiLa 2 O 2 BO 3 :Eu 3+ was co-doped with Sm 3+ , emission intensity of Eu 3+ was enhanced by ∼ 30% than that of the sample without Sm 3+ owing to the energy transfer from Sm 3+ to Eu 3+ . This energy transfer was confirmed by faster decay times of Sm 3+ as energy donors. LiLa 2 O 2 BO 3 :Sm 3+ ,Eu 3+ showed a relative brightness of 334.7% of that of Y 2 O 2 S:Eu 3+ , commercial red-emitting phosphor for n-UV LEDs.

Mechanism for strong yellow emission of Y3Al5O12:Ce3+ phosphor under electron irradiation for the application to field emission backlight units

This letter reports a strong yellow emission of Y3Al5O12:Ce3+ (YAG:Ce) mixed with ZnS:Ag,Cl under electron excitation. The penetration depths of electron of 1keV and photon of 2.7eV in YAG:Ce were estimated to be approximately 1450A and 4.65mm, respectively. Deeper penetration of blue light from ZnS:Ag,Cl helps to excite a larger number of Ce3+ in a mixture (ZnS:Ag,Cl+YAG:Ce), and YAG:Ce showed strong yellow emission via both cathodoluminescence and photoluminescence. The mixture showed the brightness of 120.5% compared to R,G,B phosphor mixture. This mixture of two phosphors was applied to a carbon nanotube field emission backlight unit.

Origin of the discrepancy between photoluminescence brightness of TAG:Ce and electroluminescence brightness of TAG:Ce-based white LED expected from phosphor brightness.

A yellow-emitting Tb(3)Al(5)O(12):Ce(3+) (TAG:Ce) phosphor was coated on blue light-emitting diodes (LEDs) to obtain white LEDs (WLEDs). Since TAG:Ce showed 90% of the brightness of Y(3)Al(5)O(12):Ce(3+) (YAG:Ce), it was expected that TAG:Ce-based WLEDs showed 90% of brightness of YAG:Ce-based ones. However, the TAG:Ce-based WLED showed 74% of the brightness of YAG:Ce-based one. Considering the density and size of the phosphors, the higher density and larger size of TAG:Ce induced a great deal of sedimentation of TAG:Ce particles in an epoxy resin. It is believed that this is one of main reasons for the reduced optical power of the TAG:Ce-based WLED compared to that of the WLED expected from the brightness of TAG:Ce.