Seung Hyok Park

Application of strontium silicate yellow phosphor for white light-emitting diodes

In order to develop a yellow phosphor that emits efficiently under the 450–470 nm excitation range, we have synthesized a Eu2+-activated Sr3SiO5 yellow phosphor and attempted to develop white light-emitting diodes (LEDs) by combining them with a InGaN blue LED chip (460 nm). Two distinct emission bands from the InGaN-based LED and the Sr3SiO5:Eu phosphor are clearly observed at 460 nm and at 570 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that InGaN (460 nm chip)-based Sr3SiO5:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460 nm chip)-based YAG:Ce.

Application of Ba2 + ∙ Mg2 + Co-doped Sr2SiO4 : Eu Yellow Phosphor for White-Light-Emitting Diodes

Large increases in the efficiency of the Sr 2 SiO 4 :Eu yellow phosphor under the 450-470 nm excitation range have been achieved by adding the co-doping element (Ba 2 + and Mg 2 + ) in the host. In order to apply to white light-emitting diodes (LEDs), we have synthesized a Ba 2 + .Mg 2 + co-doped Sr 2 SiO 4 :Eu yellow phosphor and investigated an attempt to develop white LEDs by combining it with an InGaN blue LED chip (460 nm). Two distinct emission bands from the InGaN-based LED and the Ba 2 + .Mg 2 + co-doped Sr 2 SiO 4 :Eu phosphor are clearly observed at 460 and at 560 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye.

Bredigite-structure orthosilicate phosphor as a green component for white LED: the structural and optical properties.

A green-emitting phosphor, Ca₁₄-xEuxMg₂[SiO₄]₈ (CMS:Eu²⁺), has been synthesized as a component of white light emitting diodes (WLEDs). The emission spectrum is broad, with a maximum at about 505 nm under 400 nm excitation due to the transition from the 4f⁶5d excited state to the 4f⁷-ground state of a Eu²⁺ ion. The dipole-dipole interaction was a dominant energy transfer mechanism of the electric multipolar character of CMS:Eu²⁺. The critical distance was calculated as 12.9 Å and 14.9 Å using a critical concentration of Eu²⁺ and Dexters theory for energy transfer. When CMS:Eu²⁺ and red phosphor are incorporated with an encapsulant on an ultraviolet (λmax = 395 nm) light emitting diodes (LEDs), white light with a color rendering index of 91 under a forward bias current of 20 mA was obtained. The structural and optical characterization of the phosphor is described.

Efficiency and Thermal Stability Enhancements of Sr2SiO4:Eu2+ Phosphor via Bi3+ Codoping for Solid-State White Lighting

Bi and Eu-codoped yellow-emitting phosphors of composition Sr1.95-xEu0.05BixSiO4 were prepared, and their emission and thermal quenching characteristics were investigated. The initial PL intensity and thermal quenching behaviors of Sr1.95-xEu0.05BixSiO4 were affected by the Bi-codoping as a coactivator. When 0.01 mol % of Bi was codoped to Sr1.95-xEu0.05BixSiO4, it showed an intense emission peak at 543 nm under 450 nm excitation. The peak intensity corresponds to a relative intensity of 112% of a commercial Sr2SiO4:Eu2+ phosphor (Force4 Corp.), which may be attributed to energy transfer between Bi3+ and Eu2+. The results suggest that phosphors deriving from Sr1.95-xEu0.05BixSiO4 will be a breakthrough for white light emitting diode (LEDs) and related applications in terms of efficiency enhancement and thermal stability.