Kyoung Jae Choi

Embodiment of the warm white-light-emitting diodes by using a Ba2+ codoped Sr3SiO5:Eu phosphor

The shifts of the emission band to longer wavelength (yellow-orange) of the Sr3SiO5:Eu yellow phosphor under the 450–470 nm excitation range have been achieved by adding the codoping element (Ba2+) in the host. In order to apply to white-light-emitting diodes (LEDs) with warm white and high color rendering index, we have fabricated white LEDs through the integration of the InGaN blue LED chip and the two phosphor blends (Sr2SiO4:Eu yellow phosphor +Ba2+ co-doped Sr3SiO5:Eu yellow-orange phosphor) into a single package. By employing two phosphors, covering a red region, the white LEDs show a warm white in the range of 2500–5000 K correlated color temperature and a good color rendering of over 85.

Investigation of strontium silicate yellow phosphors for white light emitting diodes from a combinatorial chemistry

In order to develop yellow phosphors that emit efficiently under the 450–470 nm excitation range, combinatorial chemistry was used based on silicate materials and investigated in an attempt to develop white light-emitting diodes (LEDs) by combining it with an InGaN blue LED chip (460 nm). Quaternary and ternary combinatorial libraries were developed to synthesize, process, and screen for silicate materials. Our combinatorial chemistry system consists of solution-based combinatorial synthesis and characterization, enabling the swift scanning of luminance. As a consequence of the combinatorial approach, several candidates were found to show high luminance under the 450–470 nm excitation range.

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.

Optical Properties of Eu2 + -Activated Sr2SiO4 Phosphor for Light-Emitting Diodes

We have synthesized a Eu 2 + -activated Sr 2 SiO 4 yellow phosphor and investigated an attempt to develop white light-emitting diodes (LEDs) by combining the phosphor with a GaN blue LED chip. Two distinct emission bands from the GaN-based LED and the Sr 2 SiO 4 :Eu phosphor are clearly observed at 400 nm and at around 550 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Also, we investigated the compositional dependence of the luminescence properties of Eu 2 + ions based on the different Mg 2 + contents.

Silicate phosphors for white LEDs identified through combinatorial chemistry

In order to develop red, green, blue phosphors that emit efficiently under the 380-410 nm excitation range, combinatorial chemistry was used based on silicate materials. We attempted to develop white UV light emitting diodes (LEDs) by combining them with an InGaN LED chip (405 nm). Quaternary and ternary combinatorial libraries were developed to synthesize, process, and screen for silicate materials. Our combinatorial chemistry system consists of solution-based combinatorial synthesis and characterization, enabling the swift scanning of luminance. As a consequence of the combinatorial approach, several red, green, and blue candidates were found to show high luminance under the 380-410 nm excitation range.

Luminescence Characteristics of Sr3MgSi2 O 8 : Eu Blue Phosphor for Light-Emitting Diodes

We have synthesized a Eu 2 + -activated Sr 3 MgSi 2 O 8 blue phosphor and investigated an attempt to develop blue light-emitting diodes (LEDs) by combining it with an InGaN blue LED chip (λ e m = 405 nm). The InGaN-based Sr 3 MgSi 2 O 8 :Eu LED lamp shows two bands at 405 and 460 nm. The 405 nm emission band is due to a radiative recombination from a InGaN active layer. This 405 nm emission was used as an optical pump for the excitation of the Sr 3 MgSi 2 O 8 :Eu phosphor. The 460 nm emission band is ascribed to a radiative recombination of Eu 2 + impurity ions in the Sr 3 MgSi 2 O 8 host matrix.

Luminescent Properties of CaSe1 − x S x : Eu and Application in LEDs

The CaSe 1-x S x :Eu phosphor, prepared by a wet-chemical method, emits visible light from reddish orange to red due to the f-d transition of Eu 2+ ions. Their emission bands are found to be shifted by sulfur substitution in the selenium sites, and such a substitution was found to influence the crystal field of surrounding Eu 2+ ions through a reduction of the lattice parameter. These phosphors are promising candidates for emitting red light for light-emitting diodes (LEDs). When mixed with a green phosphor on a InGaN-based blue chip, the as-synthesized red phosphors generated white light for LEDs.

Phosphor-Conversion White Light Emitting Diode Using InGaN Near-Ultraviolet Chip

We have synthesized a Eu2+-activated Sr3MgSi2O8 blue phosphor and (Sr,Ba)2SiO4 yellow phosphor. We fabricated a phosphor-conversion white light emitting diode(LED) using an InGaN chip that emits 400 nm near-ultraviolet(n-UV) light and phosphors that emit in the blue and yellow region. When the white LED was operated at a forward-bias current of 20 mA at room temperature(RT), the color temperature(Tcp), average color rendering(Ra), operating voltage(Vf) and luminous efficacy(ηL) were estimated to be 5800K, 72.08, 3.4V, and 7.61 lm/W, respectively. The commission International de I’Eclarirage(CIE) chromaticity coordinates obtained from the measured spectra remained almost constant during the forward-baias current increase from 0.5 mA to 60 mA.