Search

We report on the elastic properties of xMnO‐Al2O3‐(6‐x)SiO2 manganese aluminosilicate glasses, in which pronounced exchange coupling and antiferromagnetic interaction occurs among the paramagnetic Mn2+ ions. X‐ray absorption reveals a Mn‐O bond length of ∼2.1 Å, and a distance of ∼3 Å between Mn2+ ions in sixfold coordination, further corroborated by electron paramagnetic resonance and dynamic photoluminescence spectroscopy. This indicates the presence of edge‐sharing MnO6 units, in resemblance to edge‐sharing MnO8 in the crystalline Spessartine garnet Mn3Al2[SiO4]3. We argue that these cluster species have a profound effect on material stiffness: the compact structure of manganese aluminosilicate glasses enables a Young's modulus in the 100 GPa range and a Poisson's ratio of about 0.3. This exceeds the compositional trend with cation field strength observed for other aluminosilicate glasses. [ABSTRACT FROM AUTHOR]

Cd‐S‐Se quantum dot embedded glasses (QDEGs) with dual‐band emissions of green and red were synthesized by assembling two QDEGs, to obtain a color converter for white LEDs (wLEDs) with a wide color gamut and long‐term stability. Each QDEG, possessing different sizes of QD, was prepared by adjusting heat‐treatment conditions. They were then bonded to each other by an additional heat treatment to fabricate a pattern structured QDEG (pQDEG). The fabrication conditions of the pQDEGs, such as their heat‐treatment condition and thickness, were varied to improve the color gamut. pQDEG‐based WLEDs were demonstrated and their optical properties such as color coordinates, luminous efficiency, and color rendering index (CRI) were monitored. The effect of pQDEG fabrication conditions on the resultant emission spectra and color gamut were discussed. [ABSTRACT FROM AUTHOR]

Core‐shell structure in Cd‐Zn‐Se quantum dots (QDs) precipitated in the silicate glass matrix by continuous wave laser (λ = 532 nm) were demonstrated using transmission electron microscopy (TEM) and local electrode atom probe (LEAP) tomography. TEM images of the QDs in glasses after 60 min of irradiation at 9 W/cm2 show two portions with different contrasts, and diameters of 5.97 and 22.49 nm, respectively; 3D elemental distribution in these glasses from LEAP tomography shows areas of high Zn concentration near the CdSe QDs. Iso‐concentration images obtained using visualization software show that Cd‐rich clusters were not completely covered by the Zn‐rich shells in the glass after 15 min irradiation that resulted emission due to the surface defects of CdSe QDs. As the irradiation time increased to 60 min, the Zn‐rich cluster gradually surrounded the Cd‐rich core to form shells that eliminated the surface defects. During laser irradiation, CdSe QDs precipitated first due to the high degree of supersaturation of Cd and Se followed by the sequential incorporation of Zn on the Cd‐rich QDs forming shells. [ABSTRACT FROM AUTHOR]

Continuous‐wave laser (λ = 532 nm) was irradiated on Ag+‐exchanged glass surfaces to precipitate PbS quantum dots (QDs) of various diameters. TEM images combined with element mapping results confirmed the formation and size distribution of PbS QDs. Photoluminescence spectra red‐shifted from 1336 nm to 1635 nm with increases in power density and duration of laser irradiation. Three representative irradiation conditions are proposed to realize broadband photoluminescence from one glass rod to cover the 1.3‐1.7 μm communication window. [ABSTRACT FROM AUTHOR]

CdSe QDs with Cd1−xZnxSe shell structures were precipitated inside silicate glasses by continuous‐wave laser irradiation (λ = 532 nm) without any heat‐treatment process. Emission from the surface defects (λ ≈ 620 nm) was quenched significantly and the lifetimes of the band‐edge emission was increased. During the laser irradiation, Zn ions were gradually incorporated into the outer region of CdSe QDs to form Cd1−xZnxSe (0.76 ≤ x ≤ 0.8) alloy shells. [ABSTRACT FROM AUTHOR]

In this letter, a higher‐order‐mode coupler using waveguide for multimode monopulse satellite tracking and signal processing schemes handling the signal from the higher‐order‐mode coupler are proposed. The proposed higher‐order‐mode coupler uses TM01 mode for compactness and weight reduction, making it suitable for OTM satellite tracking systems. The TM01 mode is extracted from the two H‐plane slots of the circular waveguide and then divided signals are combined through magic‐T structure. Also, the sum and difference radiation patterns of antenna applicable to monopulse satellite tracking are generated. A monopulse tracking data is extracted using the proposed signal processing schemes to the antenna radiation patterns. The influence of Doppler effect and noise is concerned to enhance tracking accuracy and sliding techniques are adopted to deal with an instantaneous tracking system. Designed X‐band higher‐order‐mode coupler of TM01 mode and signal processing schemes are expected to be used for all OTM monopulse satellite tracking systems. [ABSTRACT FROM AUTHOR]

Quantum dot embedded glasses (QDEGs) were prepared by the conventional melt‐quenching method to enhance its color conversion efficiency via optimizing the concentration of ZnS, ZnSe, and CdO within the silicate‐based glass matrix. The QDEG, which contained 0.875 ZnS, 0.625 ZnSe, and 0.75 CdO (in mol%) and was heat treated at 500°C for 10 hours showed promising color conversion with an improved quantum yield of up to 25%. Color coordination of light‐emitting diodes (LEDs) mounted with the QDEGs could be adjusted by tuning heat‐treatment conditions and thickness control of QDEGs. The practical feasibility of the QDEG for a white LED is demonstrated with a reasonable glass thickness for LED packaging process. The formation of Cd‐S‐Se quantum dots within a glass matrix was identified by Raman and HR‐TEM analyses. The effect of ZnSe and CdO on the formation of Cd‐S‐Se quantum dots within silicate glass is also discussed. [ABSTRACT FROM AUTHOR]

Abstract: The influence of electric field E → on the precipitation and optical properties of PbSe quantum dots (QDs) in borosilicate glasses was investigated. Diameters of the PbSe QDs increased as E → was increased from 0.0 to 0.6 kV/mm even at the same subsequent heat treatment at 510°C for 2 hours. Increase in E → to 0.9 kV/mm caused red‐shift of the absorption and photoluminescence (PL) bands of QDs. Application of E → also led to decreases in viscosities that accelerated diffusion of ions; this phenomenon led to the formation of large QDs and resulted in the red‐shifts of the absorption and PL bands. Increase in the temperature due to Joule heating was ~38°C that led to an observed decrease in viscosities. [ABSTRACT FROM AUTHOR]

Abstract: Fluorescence intensity ratios (FIRs) of the 640 nm and 602 nm emissions from Sm3+ were recorded at various temperatures T to identify the temperature increases ΔT associated with laser‐induced local heating of Ag nanoparticles. The FIRs increased as intensities of the excitation beam from a 532‐nm continuous‐wave laser increased. Estimated T of the irradiated region increased to as high as 586°C when at laser irradiation of 1.5 W on the surface containing Ag nanoparticles. Local heating due to the surface plasmon resonance of Ag nanoparticles is a main reason for the ΔT that eventually leads to precipitation of PbS quantum dots in glasses. [ABSTRACT FROM AUTHOR]

A low sintering temperature glass based on the SiO2-P2O5-ZnO-B2O3-R2O (R=K and Na) system was studied as a matrix for embedding phosphors to fabricate color tunable white LEDs. The proposed system, which uses no heavy-metal elements and can be sintered at 500°C, incorporates thermally weak commercial phosphors such as CaAlSiN3:Eu2+ to produce phosphor-in-glasses (PiGs). Changing the mixing ratio of glass to phosphors affected the photo-luminescence spectra and color coordinates of the PiGs when mounted on a blue LED. The color rendering index (CRI) and color correlated temperature (CCT) of the LEDs were also varied with the mixing ratio, providing color tunable white LEDs. A high CRI, up to 93, as well as highly improved thermal stability were obtained, along with a low sintering temperature compared to other glass systems, suggesting the practical feasibility of the proposed system. [ABSTRACT FROM AUTHOR]

The influence of Nd2O3 addition on the precipitation kinetics of lead chalcogenide (PbS) quantum dots ( QDs) in silicate glasses was investigated. Energy dispersive X-ray spectroscopy ( EDS) indicated that the Nd3+ ions are preferentially located inside the PbS QDs rather than in the glass matrix. Changes in diameter ( D) of PbS QDs exhibited smaller time dependencies (i.e., D≈ t0.270-0.286) than that predicted by the classical Lifshitz-Slyozov-Wagner ( LSW) theory. This is due to the limited concentrations of Pb2+ and S2− ions and the large diffusion distance inside the glass matrix. In addition, extended X-ray absorption fine structure ( EXAFS) results indicated that the formation of PbS QDs was retarded due to the presence of Nd2O3 in the glasses, as the large NdO x polyhedra interrupt the diffusion of Pb2+ and S2− ions. We believe that these Nd3+ ions are primarily located in PbS QDs in the form of Nd-O clusters, and that the PbS QDs are built on top of these clusters. [ABSTRACT FROM AUTHOR]

Fluorescent glass frits were prepared and used to synthesize phosphor-in-fluorescent glass composites (PiFGs) to realize stable white light emitting diodes with high color-rendering properties. Commercial red, green, and blue phosphors were co-sintered and red phosphors were partially replaced by Eu3+ in glass frits. Phosphor-in-glass composites were placed on UV-light emitting diodes ( UV- LEDs) to generate white light. Pure white light with a luminous efficacy=58.4 lm/W, general color rendering index Ra=87 and special color rendering index for strong red R9=73 was realized with glass frits containing 7 mol% Eu2O3 and RGB ratio of 35:20:15. Luminous efficacy, Ra and R9 increased as red phosphors were replaced by red-fluorescent glass frits. [ABSTRACT FROM AUTHOR]

Modulation of the band gap energy and diameter of quantum dots (QDs) formed in glasses is important to achieve the optimized performance for applications as infrared light sources, lasers, saturable absorbers, etc. Absorption and photoluminescence of PbS QDs were extended into mid-infrared wavelength range in glasses containing small amount of lead but oversaturated with sulfur. Dual-band photoluminescence of PbSe QDs was prepared in oxyfluoride glass-ceramics containing BaF2 nanocrystals. By introducing SnO in the glasses, alloyed Pb1-xSnxSe QDs with smaller band gap energies were formed in glasses, and mid-infrared photoluminescence of Pb1-xSnxSe QDs at ~2570 nm in wavelength was achieved. [ABSTRACT FROM AUTHOR]

The influence of Nd3+ ions was investigated on the precipitation and optical properties of PbS quantum dots ( QDs) inside silicate glasses. The diameters of the PbS QDs decreased as the concentration of Nd3+ in the glass increased as evidenced by blue shifts in the absorption and photoluminescence spectra. Electron energy loss spectroscopy shows that Nd3+ ions exist preferentially inside the PbS nanocrystals rather than in the glass matrix. We postulate that Nd-O clusters are preserved during heat treatment and serve as nucleation sites for PbS crystals. No change in the local bonding scheme of the Nd3+ ions was observed following heat treatment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Silicate glasses were synthesized with additional CdO and ZnSe of varying content. When CdO was added up to 3 mol% with the amount of ZnSe fixed at 1 mol%, absorption due to Se2− color centers significantly decreased and the color of glasses was bleached without any evidence of CdSe quantum dots ( QDs). However, characteristic absorption due to CdSe QDs appeared without additional heat treatment when the ZnSe content exceeded 1.5 mol%, whereas the CdO content was fixed at 1 mol%. Raman spectra and transmission electron microscopy verified the formation of CdSe QDs. The role of CdO and ZnSe in CdSe QD formation has been discussed in relation to their structural contribution within silicate glasses. [ABSTRACT FROM AUTHOR]

Tunable absorption and photoluminescence ( PL) of lead chalcogenide quantum dots ( QDs) doped in glasses due to the quantum confinements effect have been actively investigated for application as saturable absorbers, laser sources, and fiber-optic amplifiers. Optical properties of QDs have been carefully monitored by controlling their sizes through heat treatment and rare-earth ion doping. Two- and three-dimensional precipitation of lead chalcogenide QDs were also realized using silver ion exchange and femtosecond laser irradiation in combination with thermal treatment. Prototypes of microstructured single-mode fibers and tapered fiber amplifiers containing QDs proved potentials of these materials for fiber-optic amplifiers application. Further research works on QD-doped solid core fibers, surface passivation of quantum dots and their application for the mid-infrared optical devices are necessary. [ABSTRACT FROM AUTHOR]

Luminescence of CdS quantum dots ( QDs) enhanced by the induction of Ag nanoparticles ( NPs) in glasses was investigated. Ag+ ions diffused into glasses containing CdS QDs by ion exchange, then formed Ag NPs after subsequent heat treatment. Luminescence intensity of CdS QDs increased approximately three times when the ion-exchange duration was 1 min, but was severely quenched when the duration was extended to 30 min. Increasing the amount of Ag+ ions increased the number of Ag NPs and decreased the average distance between Ag NPs and CdS QDs. This decrease in the average distance induced the changes of luminescence intensity. [ABSTRACT FROM AUTHOR]

A method is reported that uses visible continuous-wave laser to directly fabricate micropatterns in glasses containing silver ( Ag) nanoparticles. Ag nanoparticles were formed in the glass using thermal treatment. Upon laser irradiation, Ag nanoparticles with their surface plasmon in resonance with the laser beam were partially melted and decreased in size due to the temperature increase induced by the excited Ag nanoparticles. Three-dimensional patterns were achieved by scanning the laser beam through the thickness of the glass. [ABSTRACT FROM AUTHOR]

This article reports the effect of Ag+ ion-exchange on the precipitation of PbS quantum dots ( QDs) in silicate glasses. The glasses were subjected to ion-exchange in AgNO3 salt melts at 260°C for 60 s. Ag nanoparticles ( NPs) and PbS QDs precipitated after heat treatment at temperatures of 440°C-460°C for 10 h. Photoluminescence wavelength λPL of PbS QDs was longer (~1525 ≤ λPL ≤ ~1580 nm) in Ag+ ion-exchanged regions than in Ag+-free regions (~1030 ≤ λPL ≤ ~1200 nm). Average diameter D of PbS QDs estimated by calculation and TEM images was larger in Ag+ ion-exchanged regions (~5.2 ≤ D ≤ ~5.5 nm) than in Ag+-free regions (~2.4 ≤ D ≤ ~3.3 nm). Ag NPs that formed during heat treatment provided the sites for heterogeneous nucleation of PbS QDs and promoted the precipitation of PbS QDs in glasses. [ABSTRACT FROM AUTHOR]

Silicate glasses containing CdS and Ag2O were made by the melt-quenching method. CdS quantum dots ( QDs) were precipitated inside the glass matrix by heat treatment at 570-590 °C for 10 h, and the influence of Ag on photoluminescence ( PL) of CdS QDs was investigated. The emission located at 478-493 nm in wavelength originated from the direct recombination of electron/hole pairs was quenched due to charger transfer between Ag and CdS QDs. Modification of PL from CdS QDs by Ag provides potentials toward developing the color changing materials for light-emitting diodes ( LEDs). [ABSTRACT FROM AUTHOR]

Emission properties and energy transfer of PbO-Bi2O3-Ga2O3-GeO2 glasses codoped with Tm3+ and Tb3+ ions were investigated. The 1.48-μm emission due to the Tm3+ : ³H4→³F4 transition can be used to amplify the S-band (1460-1530-nm) signal light. With Tb3+ addition, the lifetime and emission intensity of the Tm3+ : ³F4 level decreased sharply via the Tm3+ : ³F4 → Tb3+ : 7 F0.12 energy transfer. Population densities of the ³F4 and ³H4 levels in Tm3+ calculated from rate equations clearly verified that population inversion in Tm3+ ions became possible with as little as 0.1 mol% of Tb3+ addition. [ABSTRACT FROM AUTHOR]

Emission properties and energy transfer of PbO-Bi2O3-Ga2O3-GeO2 glasses codoped with Tm3+ and Tb3+ ions were investigated. The 1.48-μm emission due to the Tm3+ : ³H4→³F4 transition can be used to amplify the S-band (1460-1530-nm) signal light. With Tb3+ addition, the lifetime and emission intensity of the Tm3+ : ³F4 level decreased sharply via the Tm3+ : ³F4 → Tb3+ : 7 F0.12 energy transfer. Population densities of the ³F4 and ³H4 levels in Tm3+ calculated from rate equations clearly verified that population inversion in Tm3+ ions became possible with as little as 0.1 mol% of Tb3+ addition. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The preferential incorporation of Er3+ ions into the PbF2 nanocrystals during the ceraming process of oxyfluoride glass was analyzed using electron energy loss spectroscopy analysis. Concentrations of Er3+ ions were considerably higher in PbF2 nanocrystals compared to those in the glass matrix. Changes in lineshapes of absorption spectra from Er3+: 4 I15/2→4 I13/2 transition and lifetimes of the excited-state Er3+ (4 S3/2 level) ions also supported the incorporation of Er3+ ions into PbF2 nanocrystals. [ABSTRACT FROM AUTHOR]