Jong Heo

Vitrification of fly ash from municipal solid waste incinerator.

Fly ash from municipal solid wastes (MSW) incinerators in Korea contains a large amount of toxic materials and requires pertinent treatments. However, since fly ash in Korea has a high chlorine concentration, it is difficult to apply cementation and chemical treatment techniques. In this study, we report the vitrification of fly ash along with the properties of the glasses and leaching characteristics of heavy metal ions. Fly ash can be vitrified by melting at 1500 degrees C for 30 min with the addition of >5 wt.% of SiO2. Glasses showed Vickers hardness of 4000-5000 MPa, bending strength of 60-90 MPa and indentation fracture toughness of approximately 0.9 MPa m(1/2). Glasses also showed the excellent resistance against leaching of heavy metal ions with Cd2+ <0.04 ppm, Cr3+ <0.02 ppm, Cu2+ <0.04 ppm and Pb2+ <0.2 ppm. These results indicate that the vitrification technique is effective for the stabilization and recycling of toxic incinerator fly ash.

Raman spectroscopic analysis on the solubility mechanism of La3+ in GeS2–Ga2S3 glasses

Abstract In comparison to other chalcogenide glasses, Ge–Ga–S glasses have the largest rare-earth solubility. Raman spectra of GeS2–Ga2S3 glasses contain two bands at 265 and 385 cm−1 which increased in intensity with the addition of Ga2S3. These are associated with the vibration of Ge–Ge bonds and edge-shared GaS4 tetrahedra, respectively. Upon the addition of La2S3 into GeS2–Ga2S3 glasses, intensities of these two bands decreased while a new band appeared at 375 cm−1 due to the vibration of tetrahedra with non-bridging sulfur(s). Dissociation of Ge–Ge bonds and edge-shared GaS4 tetrahedra through the addition of La2S3 are responsible for the non-bridging sulfur formation. La3+ can be dissolved into the glass network as charge compensators for these non-bridging sulfurs. Since no such structural unit is present in glasses without Ga2S3, this connection scheme and the structural modification in Ga-containing chalcogenide glasses seem to be crucial for an increase of La3+ solubility.

1.3 μm emission and multiphonon relaxation phenomena in PbOBi2O3Ga2O3 glasses doped with rare-earths

Abstract The 1.3 μm fluorescent emissions from PbOBi 2 O 3 Ga 2 O 3 glasses doped with Pr 3+ or Dy 3+ were measured. Modified Judd—Ofelt analysis was applied to the Pr 3+ -doped glasses to obtain intensity parameters and radiative properties. Emission from the Pr 3+ : 1 G 4 → 3 H 5 transition in heavy metal oxide (HMO) glass was centered at the wavelength of 1320 nm with a spectral bandwidth of 100 nm. The lifetime of the 1 G 4 level was 53 μs with a quantum efficiency of 9%. Excited-state absorption near the 1.3 μm emission were comparable to those in fluoride glasses. Multiphonon relaxation rates in PbOBi 2 O 3 Ga 2 O 3 glasses calculated from the lifetimes were similar to those of fluoride glasses, but were the smallest among oxide glasses.

Phosphor in glasses with Pb-free silicate glass powders as robust color-converting materials for white LED applications

Phosphor-in-glass (PiG) typed robust color converters were fabricated using Pb-free silicate glasses for high-power white LED applications. SiO2-B2O3-RO(R=Ba,Zn) glass powder showed good sintering behavior and high visible transparency under the sintering condition of 750 °C for 30 min without noticeable interaction with phosphors. By simply changing the thickness of the PiG plate or mixing ratio of glass to Y3Al5O12:Ce3+ phosphor, CIE chromaticity coordinates of the LED can be easily controlled. Enhanced thermal quenching property of PiG compared to phosphor with conventional silicone resin suggests its prominent feasibility for high-power/high-brightness white LEDs.

Absorption and mid-infrared emission spectroscopy of Dy3+ in Ge-As(or Ga)-S glasses

Abstract Ge-As-S and Ge-Ga-S glasses doped with Dy 3+ were prepared and the emission characteristics of four infrared fluorescent emissions at 1.33, 1.75, 2.90 and 4.38 μm were evaluated. High oscillator strengths and large intensity parameters of Dy 3+ originate from the highly covalent nature of the bonds in the glasses. Measured lifetimes in the Ge-As-S glass are 728 and 4550 μs for the 6 H 11/2 → 6 H 15/2 (1.75 μm) and 6 H 13/2 → 6 H 15/2 (2.90 μm) transitions, respectively. Quantum efficiencies of 32.8 and 87.2% of the above transitions compare well with the values reported previously. Multiphonon relaxation rates in Ge-As-S and Ge-Ga-S glasses are4 orders of magnitude less than those in silicate glasses, which provide good opportunities for future laser applications.

Comparative study of energy transfers from Er3+ to Ce3+ in tellurite and sulfide glasses under 980 nm excitation

We have demonstrated that the population feeding from the 4I11/2 level to the 1.5 μm fluorescence emitting 4I13/2 level of Er3+ ions in low phonon energy glass hosts can be enhanced by codoping with Ce3+ under optical pumping at 980 nm. The nonradiative energy transfer Er3+: 4I11/2; Ce3+: 2F5/2→Er3+: 4I13/2; Ce3+: 2F7/2, occurs in the form of phonon-assisted energy transfer, and therefore the feeding rates are faster in the tellurite glasses, which have a comparatively higher phonon energy than in the sulfide glasses. The cross-relaxation process for 4I13/2: 4I13/2→4I15/2: 4I9/2, which lowers the population density of the 4I13/2 manifold and causes a deleterious effect in the 1.5 μm fluorescence intensity, is more severe in the sulfide glasses. Population feeding rate from the 4I11/2 to the 4I13/2 level is significantly enhanced by way of cerium codoping into tellurite glasses, which promises an efficient 980 nm pumped broadband Er3+-doped fiber amplifier.

Remote fiber-optic chemical sensing using evanescent-wave interactions in chalcogenide glass fibers

An infrared-transmitting chalcogenide fiber was used as an optical probe to analyze qualitatively and quantitatively various chemical substances in aqueous solutions. An unclad fiber with 380-microm diameter was combined with a Fourier transform infrared spectrometer to monitor the concentration of the analytes in solutions by measuring the changes in the absorbance of their fundamental vibration peaks. A linear relationship was observed between the absorption by the vanescent field and concentrations of various analytes. For this study low concentrations of acetone, ethyl alcohol, and sulfuric acid were detected in aqueous solutions. The minimum detection limit for these three chemical substances was 5, 3, and 2 vol. %, respectively, with a sensor length of 15 cm. It was also demonstrated that the same sensor design is capable of monitoring gaseous species such as dichlorodifluoromethane.

Emission properties of the Er3+:4I11/2→4I13/2 transition in Er3+- and Er3+/Tm3+-doped Ge–Ga–As–S glasses

Abstract Ge–Ga–As–S glasses were investigated to develop efficient host materials for the Er 3+ :2.7 μm fiber lasers. Ge30Ga1As9S60 and Ge30Ga2As6S62 (all in at.%) glasses show good thermal stability and high rare-earth solubility up to 0.3 mol%. Mid-infrared emission with a peak wavelength of 2.76 μm and bandwidth of ∼120 nm was observed in Er3+- and Er3+/Tm3+-doped Ge30Ga2As6S62 glasses. Codoping of Tm3+ significantly reduced the lifetime of the Er 3+ : 4 I 13/2 level due to the energy transfer of Er 3+ : 4 I 13/2 → Tm 3+ : 3 F 4 . Thus, the population inversion between the 4 I 11/2 and 4 I 13/2 levels in Er3+ became possible. In Er3+-doped glasses, the rate of cross-relaxation for the 4 I 11/2 level was approximately 11 times faster than that for the 4 I 13/2 level.

1.6 μm emission from Pr3+: (3F3,3F4)→3H4 transition in Pr3+- and Pr3+/Er3+-doped selenide glasses

1.6 μm emission originated from Pr3+: (3F3,3F4)→3H4 transition in Pr3+- and Pr3+/Er3+-doped selenide glasses were investigated under an optical pump of a conventional 1480 nm laser diode. The measured peak wavelength and full width at half maximum of the fluorescent emission were ∼1650 and >100 nm, respectively. A moderate lifetime of the thermally coupled upper manifolds (∼212±5 μs) together with a high stimulated emission cross section of ∼(3±1)×10−20 cm2 promises to be useful for 1.6 μm band fiber-optic amplifier that can be pumped with an existing high-power laser diode. Codoping of Er3+ significantly enhanced the emission intensity by way of a nonradiative Er3+: 4I13/2→Pr3+: (3F3,3F4) energy transfer.

Multiphonon and cross relaxation phenomena in GeAs(or Ga)S glasses doped with Tm3

Abstract Multiphonon and cross relaxation phenomena in Tm 3+ -doped Ge 30 As 10 S 60 and Ge 25 Ga 5 S 70 (at%) glasses were evaluated and compared with other glass hosts. Multiphonon relaxation rates, as obtained from the measured and predicted radiative lifetimes, were orders of magnitude less than those in most oxide glasses. Cross relaxation associated with 3 H 4 , 3 H 6 → 3 F 4 , 3 F 4 transitions was less significant in Ge 25 Ga 5 S 70 glass than in Ge 30 As 10 S 60 glass and were comparable to those in fluoride glasses. Oscillator strengths and intensity parameters of Tm 3+ in both sulfide glasses were larger mainly due to the covalent nature of bonds in glasses.