Showing papers by "Jong Heo published in 2014"

Control of chromaticity by phosphor in glasses with low temperature sintered silicate glasses for LED applications

Abstract: Phosphor-in-glass (PiG) color converters for LED applications were fabricated with a mixture of phosphors, Y₃Al₅O₁₂:Ce³⁺ (yellow) and CaAlSiN₃:Eu²⁺ (red). The low sintering temperature (550°C) of SiO₂-Na₂O-RO (R=Ba, Zn) glass powder enabled the inclusion of CaAlSiN₃:Eu²⁺ (red) phosphor which cannot be embedded with conventional glass powders for PiGs. By simply varying the mixing ratio of glass to phosphors as well as the ratio of yellow to red phosphors, the facile control of the CIE chromaticity coordinates and correlated color temperature of the LED following the Planckian locus has been achieved. Phosphors were well distributed within the glass matrix without noticeable reactions, preserving the enhanced thermal quenching property of the PiG compared to those with silicone resins, for LEDs.

Stable and Color‐Tailorable White Light from Blue LEDs Using Color‐Converting Phosphor–Glass Composites

Abstract: Commercial Ce3+:YAG phosphors were embedded in glass frits. Thermal condition for the viscous sintering of the composite materials was optimized. The phosphor–glass composites had maximum external efficiency of 30% and maximum light extraction efficiency of 39%. Color temperatures of the composites composed of fluorescent glass frits containing Eu3+ and Mn2+ combined with blue LEDs shifted from ~7000 to ~4000 K.

Infrared photoluminescence from lead sulfide quantum dots in glasses enriched in sulfur

Abstract: Formation of PbS QDs in the glasses containing a small amount of lead oxide was examined. Oversaturation of sulfur only was sufficient to promote the formation of PbS QDs in the glasses. Upon thermal treatment, absorption of PbS QDs was tuned from 824 nm to 2213 nm. Infrared photoluminescence, especially, mid-infrared photoluminescence from PbS QDs was observed in the range of 1008 nm to 2182 nm. Ostwald ripening of PbS QDs occurred when the heat-treatment temperature was 530 °C or 540 °C, and led to the decrease in the absorption coefficients and splitting of the photoluminescence bands.

Infrared emission from Er3+/Y3+ co-doped oxyfluoride glass-ceramics

Abstract: Infrared emission properties of oxyfluoride glasses with nominal compositions of 55SiO 2 –10Al 2 O 3 –(35 − x − y)PbF 2 –xErF 3 –yYF 3 (in mol%) with x = 0.1, 0.2, 0.3, or 0.5 and y = 0, or 1.0, were investigated. YF 3 was doped into the glasses to overcome the concentration quenching and achieve efficient infrared emission from Er 3 + doped oxyfluoride glass-ceramics. It was found that introduction of YF 3 can efficiently promote the formation of Er 3 + -doped fluoride nanocrystals even when the doping concentration of ErF 3 was low. With the doping of YF 3 , infrared emission was significantly enhanced and strong infrared emissions at 980 nm and 2730 nm bands were observed. Prolongation of lifetimes of Er 3 + : 4 I 13/2 and 4 I 11/2 energy levels showed that concentration quenching of the infrared emissions was greatly suppressed. These results indicate that oxyfluoride glass-ceramics co-doped with Y 3 + have potentials for efficient infrared applications.

Lead sulfide quantum dots in glasses containing rare-earth ions

Abstract: The size and spatial distribution of PbS QDs in glasses need to be controlled in order to achieve desired optical characteristics. This paper reports on the use of several rare-earth oxides such as Ho2O3, Er2O3, and La2O3 to control the size of PbS QDs in silicate glasses. Additions of rare-earth oxides result in blue shifts of the absorption bands from 1344 nm to 930 nm, and the wavelengths of PL bands can be controlled between 1421 nm and 1035 nm. Additions of up to 0.8 mol% of Ho2O3 decreased the diameters of PbS QDs from 4.82 nm to 3.02 nm. The same tendencies were found for both Er2O3 and La2O3 additions, although the size of PbS QDs increased as the ionic radius of rare-earth ions increased. It is proposed that clusters of RE–O bonds act as nucleating agents for the precipitation of PbS QDs.

Down-conversion in Tm3 +/Yb3 + doped glasses for multicrystalline silicon photo-voltaic module efficiency enhancement

Abstract: Efficiency enhancement of a multicrystalline silicon solar cell using down-conversion of Tm3 + and Yb3 + doped silicate glasses was investigated. Na2O–CaO–SiO2 glasses doped with Tm3 + or Tm3 + and Yb3 + were prepared. Distributed Bragg Reflector (DBR) coatings were sputtered on the glass surface to control the transmission and reflection of the desired portion of the solar spectrum. These were placed on a multicrystalline silicon solar cell in combination with a solar spectrum simulator. The efficiency of solar cell with Tm3 + or Tm3 + and Yb3 + doped glasses increased compared to as-prepared glass without rare-earth addition. The efficiency of solar cell with rare earth doped glasses was re-measured three times with same samples, and the real efficiency enhancement can be proved. The potentials, limitations and future perspectives of rare-earth doped glasses with DBR structure on the efficiencies of PV modules were discussed.

Plasmon-Assisted Precipitation of PbS Quantum Dots in Glasses Containing Ag Nanoparticles

Abstract: PbS QDs of ~ 5nm diameter were precipitated in glasses containing Ag nanoparticles after 3 min of 1.5-W continuous-wave laser illumination at λ = 532 nm. Photoluminescence spectra of the PbS QDs recorded in the 1.3~1.6 μm wavelength region revealed conversion of photon energy to thermal energy by surface plasmon resonance. Laser-assisted local heating around Ag NPs can provide a new method to control the spatial distribution of QDs in glasses.

Direct observation of Nd3+ and Tm3+ ions distributions in oxyfluoride glass ceramics containing PbF2 nanocrystals

Abstract: Nd{sup 3+} and Tm{sup 3+}, doped oxy-fluoride glasses and glass ceramics were prepared by conventional melt-quenching and subsequent heat-treatment, respectively. β-PbF{sub 2} nanocrystals with diameter 50 –100 nm formed in the glass matrix after heat treatment. The Stark splitting in absorption peaks, enhanced photoluminescence and prolonged lifetimes that β-PbF{sub 2} nanocrystal formation increased the luminescence of rare earth ions. Both Nd{sup 3+} and Tm{sup 3+} ions were incorporated into nanocrystals that were enriched in lead and fluorine, and deficient in oxygen. - Highlights: • EELS analysis for rare-earth ion distribution in oxy-fluoride glass ceramics • No significant changes in lifetimes of Nd{sup 3+}, while obvious change for Tm{sup 3+} • Direct evidence of Nd{sup 3+} and Tm{sup 3+} aggregation into fluoride nanocrystals.

Nanocrystal Formation in Glasses Controlled by Rare Earth Ions

Abstract: Distribution and roles of rare earth ions in fluoride nanocrystals and lead chalcogenide quantum dots formed in glasses are reported. High-resolution transmission electron microscopic analysis and electron energy loss spectroscopic (EELS) analysis showed that oxyfluoride glasses initially form crystals with high Er3+ content such as PbErF5 during heating and gradually form crystals with low Er3+ concentration. Amount of PbErF5 crystals depended upon the initial concentration of Er3+ ions in the parent glasses. EELS analysis also showed that Nd3+ ions were formed inside PbS quantum dots, supporting the proposition of the formation of Nd-O clusters.

Precipitation of PbS quantum dots in glasses by thermal diffusion of Ag+ ions from silver pastes

Abstract: Precipitation of PbS quantum dots (QDs) in glasses was controlled by thermal diffusion of Ag + ions from Ag paste at a temperature of 320 °C. After subsequent heat treatment at 420–450 °C, PbS QDs formed in the near-surface regions where the silver paste was applied. After the glasses were heat-treated at 440 or 450 °C, PbS QDs were larger in Ag-affected surface regions than in Ag-free glasses. PbS QDs grew in Ag-affected regions when they were heat-treated at 420 or 430 °C. Ag + ions penetrated ~ 25 μm from the glass surface after thermal diffusion of Ag + ions and subsequent heat treatment at 430 °C. Thermal diffusion of Ag + ions from Ag paste is a viable method to control the precipitation and spatial distribution of PbS QDs in glasses.

980 nm upconversion luminescence from oxy-fluoride glasses and glass-ceramics doped with Yb3 +and Er3 + ions

Abstract: Infrared upconversion luminescence properties of Er 3 + /Yb 3 + co-doped oxy-fluoride glasses and glass-ceramics were investigated. Under 1550 nm laser excitation, infrared emission centered at ~ 980 nm that originated from the Yb 3 + : 2 F 5/2 → 2 F 7/2 and Er 3 + : 4 I 11/2 → 4 F 15/2 transitions was observed. The upconversion luminescence was enhanced both by Yb 3 + content increase and by precipitation of β-PbF 2 nano-crystals in the glass matrix. The energy transfer process between Yb 3 + and Er 3 + ions dominated IR upconversion emission, and Yb 3 + can be used as energy acceptor. The strong upconverted luminescence can be used to increase the efficiency of silicon solar cells.

Dual-band photoluminescence of lead selenide quantum dots doped oxyfluoride glass-ceramics containing BaF2 nanocrystals

Abstract: In this work, PbSe QDs were precipitated in oxyfluoride glass-ceramics containing BaF2 nanocrystals. Tunable and broad absorption and photoluminescence from PbSe QDs doped glass-ceramics were observed in the near-infrared wavelength range. When the glasses were heat-treated at temperatures below 560 °C using one-step heat-treatment schedule, single photoluminescence band was observed from each sample. Upon high temperature (560 °C or 570 °C) one-step or two-step heat-treatment, dual-band photoluminescence was observed. These two photoluminescence bands in each spectrum were separated by a gap of ~ 110–150 meV, and as a result, effective full width at half maximum as large as ~ 500 nm was recorded.

Compositional dependency of upconversion luminescence of Nd3 + doped Ge–Ga–S–CsBr chalcohalide glasses

Abstract: The effects of host glass composition on the upconversion luminescence of Nd3 + doped (1 − x)(Ge0.25Ga0.10S0.65)–x(CsBr) chalcohalide glasses were investigated. Bright upconversion luminescence was observed in the 535 nm, 602 nm and 665 nm bands, with weak blue emission. Luminescence intensity increased with CsBr content x, and jumped when x increased from 0.08 to 0.10. Lifetimes of 4G7/2 level and 4F3/2 intermediate levels of Nd3 + ions had similar dependency on CsBr content. Raman analysis proved that a [GaS3/2Br]− group formed due to CsBr addition. The effective phonon energy decreased from 375 cm− 1 ([Ga–S] bond vibration) to 245 cm− 1 ([Ga–Br] bond vibration) when CsBr/Ga ratio was > 1, which resulted in sudden changes in upconversion intensities and lifetimes. The results indicated that the chalcohalide glasses are promising candidates for use in applications that require efficient upconversion luminescence.

Evolution of Strong Red Upconversion Luminescence in Er3+‐Containing Oxy‐Fluoride Glass and Glass‐Ceramics

Abstract: The Er3+ concentration dependencies of upconversion luminescence in oxy-fluoride glass and glass-ceramics containing PbF2 nanocrystals were investigated. Strong red emission from the 4F9/2 → 4I15/2 transition was observed with the addition of ~0.8 mol% Er3+ ions, whereas ~10 mol% of Er3+ is required to achieve such emission in several other crystalline hosts. Intensities of red emission further increased with the formation of nanocrystals through heat treatment. The Er3+ ions enriched in glass and segregated preferentially inside the PbF2 nanocrystals that decreased the distance among Er3+ ions and thereby facilitated energy transfer.

Glass-phosphor composite containing rare-earth ion and light-emitting diode including same

Abstract: A method of manufacturing a glass-phosphor composite is disclosed. The method comprises: preparing rare earth ion-containing parent glass; mixing the rare-earth ion-containing parent glass in a power state with a phosphor in a powder state; and providing a glass-phosphor composite using the powder mixture of the rare earth ion-containing parent glass and the phosphor, wherein the mixing includes mixing the rare earth ion-containing parent glass in the powder state with the phosphor in the powder state so that the phosphor in the glass-phosphor composite is in an amount of 5 wt % to 30 wt %, and the preparing includes using a glass frit having a glass transition point of 300° C. to 800° C. and a sintering temperature of 200° C. to 600° C.

White light emitting device using uv led chip

Abstract: The present invention discloses a white light emitting device that includes: a substrate; a UV LED chip mounted on the substrate; and a glass-fluorescent body complex arranged on a location through which a UV ray from the UV LED chip passes. The glass-fluorescent body complex is made by mixing 5-30 wt% of fluorescent bodies in multiple kinds, which generate the white light with the UV LED chip, and 70-95wt% of glass frits.

Soft inorganic substance-phosphor composite and light emitting device comprising the same

Abstract: The present invention discloses a light emitting device that includes: a substrate; an LED chip mounted on the substrate; and a soft inorganic substance-fluorescent substance composite arranged on a location through which light from the LED chip passes. The soft inorganic substance-fluorescent substance composite includes 5-50 wt% of one or more fluorescent substances, which is excited by light from the LED chip and emits light in a different wavelength, and includes 50-95 wt% of a soft inorganic carrier that carries the fluorescent substance.

Glass strenthening method by 2-step ion exchange

Abstract: The present invention provides a method for strengthening glass through two-step ion exchange performed in alkali metal mixed salt and alkali metal single salt Compressive stress and ion penetration depth are independently controlled and improved using the method

Rare earth ion added glass-phosphor composite and light emitting diode comprising the same

Abstract: A method for manufacturing a glass-phosphor composite containing rare-earth ion is disclosed, and the method comprises: a mother glass manufacturing step for manufacturing mother glass containing rare-earth ion; a mixing step for mixing the mother glass containing rare-earth ion and a phosphor in a powder state; and a composite manufacturing step for manufacturing a phosphor-glass composite by using mixed powder of the mother glass containing rare-earth ion and the phosphor.