Showing papers by "Jong Heo published in 2010"

Optical properties of CdSe quantum dots in silicate glasses

Abstract: CdSe quantum dots (QDs) were precipitated in silicate glasses under various durations and temperatures of heat-treatment Absorption and photoluminescence (PL) spectra of the QDs showed the quantum confinement effect from CdSe QDs When the glass was heat-treated for 10 h, estimated average QD sizes increased from 52 nm when the glass was heat-treated at 490 °C and to 69 nm when it was treated at 500 °C When the glass was heat-treated at 480 °C, estimated average QD sizes were 49 nm after 20 h and 53 nm after 30 h The PL peak position was independent of the excitation wavelengths; this result indicates that the size distribution of CdSe QDs was narrow

Spatial distribution of rare-earth ions and GaS4 tetrahedra in chalcogenide glasses studied via laser spectroscopy and ab initio molecular dynamics simulation

Abstract: The spatial distribution of ${\text{Nd}}^{3+}$ ions and ${\text{GaS}}_{4}$ tetrahedral units in Nd-doped Ge-As-Ga-S glasses has been studied by laser spectroscopy and ab initio molecular dynamics (MD) simulations. A sharp increase in ${\text{Nd}}^{3+}$ fluorescence intensities and lifetimes was observed with increasing Ga content, and attributed to the formation of tightly bound ${\text{Nd}}^{3+}$ clusters in Ga-free glasses and the subsequent dissolution of such clusters upon Ga doping. A large modification in ${\text{Nd}}^{3+}$ sites was also identified from low-temperature site-selective excitation spectra, suggesting preferential spatial correlations between ${\text{Nd}}^{3+}$ and ${\text{GaS}}_{4}$ tetrahedra even at low Ga-doping levels. MD simulations of these materials in the liquid state showed a tendency for Ga cluster formation as well as spatial correlations between Nd and Ga atoms consistent with the experimental results. On the basis of this result, a comprehensive structural model for Nd- and Ga-doped sulfide glasses is proposed.

Lead Sulfide Quantum Dots Formation in Glasses Controlled by Erbium Ions

Abstract: This paper reports the effect of Er 2 0 3 concentration on nucleation and optical properties of PbS quantum dots (QDs) formed in a silicate glass under heat treatment at 490° or 500°C. As Er 2 0 3 concentration increased from 0.1 to 0.4 mol%, average radii of PbS QDs decreased from ~5 to ~4 nm, and peak wavelengths of absorption and photoluminescence also decreased. Clusters of Er 3+ ions connected by bridging oxygens may act as the nucleation centers for PbS QDs.

Local Heating from Silver Nanoparticles and Its Effect on the Er3+ Upconversion in Oxyfluoride Glasses

Abstract: The effect of silver (Ag) nanoparticles on the upconversion emission properties of Er 3+ ions in oxyfluoride glasses was investigated, and a mechanism of the energy transfer proposed. The integrated intensity ratios between 522 and 545 nm emission bands of Er 3+ ions in glasses containing Ag nanoparticles were strongly dependent on the size of the Ag nanoparticles as well as on the intensity of the 800 nm excitation laser. When the absorption of Ag nanoparticles overlapped with the 2 H 11/2 and 4 S 3/2 energy levels in Er 3+ ions, a strong energy transfer occurred from Er 3+ : 2 H 11/2 , 4 S 3/2 levels to Ag nanoparticles. This energy was then converted to a temperature rise in the vicinity of Er 3+ ions, eventually leading to the large increase in the integrated intensity ratios. The estimated effective temperature was approximately 200 K higher than the experimental temperature when the excitation power was 700 mW.

New functional glasses containing semiconductor quantum dots

Abstract: CdSe and PbSe quantum dots (QDs) were precipitated in oxide glass matrices and their optical properties were investigated. The size of QDs could be controlled using careful heat treatment. The quantum confinement effect was clearly observed, as evidenced by a shift in the peak wavelengths of absorption. It was possible to control also the wavelength of the photoluminescence bands of CdSe and PbSe QDs by using thermal treatment.

Up-conversion fluorescence and low-temperature emission in Er3+-doped GeGaS–CsBr glasses

Abstract: Optical properties of Er-doped chalcohalide GeGaS–CsBr glasses have been investigated as a function of Er and Ga concentrations. Nominal compositions of (Ge 0.25 Ga. 0.10 S 0.65 ) 0.9 (CsBr) 0.1 and (Ge 0.23 Ga. 0.12 S 0.65 ) 0.9 (CsBr) 0.1 glassy hosts have been chosen for this study. The effects of Er content and host composition on 1.5 μm emission of Er 3+ ions, measured at low-temperature of 20 K under excitation by 514.5 nm, have been specified. Besides, the up-conversion fluorescence of Er 3+ ions pumped at 795 nm is reported. Two intense emission bands in the green and one weak emission band in the red regions around 530, 554 and 644 nm have been observed, and were attributed to 2 H 11/2 → 4 I 15/2 , 4 S 3/2 → 4 I 15/2 , and 4 F 9/2 → 4 I 15/2 transitions of Er 3+ ions, respectively. The simplified energy-level diagram of Er 3+ ion has been used to identify the observed up-conversion fluorescence bands in visible region.

Photo-Induced Effect in Heavy Metal Oxide Glasses

Abstract: Photo-induced phenomena in binary (PbO–Ga2O3) and ternary (PbO–Bi2O3–Ga2O3) heavy metal oxide glasses were investigated. A red shift up to ∼0.05 eV in the absorption edge of 75PbO–25Ga2O3 glass (mol%) was observed by illuminating the subbandgap light for 30 min. This shift was completely erased by the heat treatment near the glass transition temperature. Refractive index of the glass at 600 nm also increased ∼0.011 by the illumination. It is believed that the presence of lone-pair electrons associated with Pb-polyhedra is essential to realize a reversible photo-induced effect in these oxide glasses.

Nd3+ sensitized blue upconversion luminescence in Nd3+/Pr3+ co-doped Ge–Ga–S–CsBr chalcohalide glasses

Abstract: The effect of CsBr/Ga ratio on the blue upconverted emission from Nd3+/Pr3+ in Ge–Ga–S–CsBr chalcohalide glasses was investigated. When CsBr/Ga was smaller than unity, the energy transfer from Nd3+ to Pr3+ ions was dominant and blue emission centered at ∼ 495 nm (Pr3+:3P0 → 3H4) was observed. On the contrary, the intensity of the upconversion luminescence from Nd3+ increased at the expense of the blue emission when CsBr/Ga ratio exceeded unity. The possible relationship between the composition-dependent blue emission and the local environment of rare earth ions was discussed.