Kyoung Hyuk Jang

Optical spectroscopy, 1.5μm emission, and upconversion properties of Er 3+ -doped metaphosphate laser glasses

Metaphosphate glasses doped with five concentrations of Er3+ ions have been investigated through absorption and emission spectra, decay curves, and upconversion measurements. Judd-Ofelt parameters have been evaluated from absorption spectrum of the 1.0mol.%Er3+-doped glass, which are in turn used to predict radiative properties of some important luminescence levels of Er3+ ions in these glasses. Gain bandwidths of an optical amplifier have been evaluated and are compared with those of reported Er3+:glass systems. Temperature dependence of the 1.5μm emission has been studied for the 2.0mol.%Er3+-doped glass from 13K to room temperature. Lifetimes of the I13/24 level were measured and are found to decrease with concentration of Er3+ ions after 0.1mol.%. Concentration quenching of lifetimes has been analyzed using the theory developed by Auzel [J. Lumin.94-95, 293 (2001); Opt. Mater.24, 103 (2003)]. Infrared to visible upconversion was also measured for three concentrations of Er3+-doped metaphosphate glasses with 794nm excitation. A mechanism, involving excited state absorption and energy transfer upconversion, has been proposed to explain the upconversion process.

White light generation in Dy 3+ -doped oxyfluoride glass and transparent glass-ceramics containing CaF 2 nanocrystals

The radiative emission properties of the Dy3+ ions in an oxyfluoride glass and glass-ceramics have been studied for the generation of white light. The x-ray diffraction pattern of the glass-ceramics shows the formation of CaF2 fluorite-type nanocrystals in the glass matrix after a suitable thermal treatment of the precursor glass, whereas time-resolved optical measurements show the incorporation of the Dy3+ ions in the CaF2 nanocrystals. Intense white light has been observed when the samples are excited with 451 nm laser light. From the visible emission spectra, yellow to blue intensity ratios and the chromaticity color coordinates have been determined. All the color coordinates are found to lie in the white light region of the chromaticity color diagram.

Spectral investigations on Dy3+-doped transparent oxyfluoride glasses and nanocrystalline glass ceramics

Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and studied by x-ray diffraction, absorption, and visible and near-infrared emission spectra. The samples emit intense white light when populating the F49/2 level with a 451 nm laser light and, from the visible emission spectra, yellow to blue intensity ratios and chromaticity color coordinates have been calculated and their relative variation have been discussed based on the concentration of Dy3+ ions and the heat treatment conditions used to prepare the glass ceramics. Infrared emission has also been observed in glasses and glass ceramics after laser excitation at 800 nm, showing bands at 1.33 and 1.67 μm, useful for optical amplification in fiber amplifiers.

Optical and site-selective spectral studies of Eu3+-doped zinc oxyfluorotellurite glass

The Eu3+-doped zinc oxyfluorotellurite (TZLFE) glass of molar composition 59TeO2–20ZnO–20LiF–1Eu2O3 has been prepared and studied by broadband, Raman, and fluorescence-line narrowing (FLN) spectral techniques to investigate the local environments of Eu3+ ions in this glass. From the vibronic spectra, different TeO groups coupled to Eu3+ ions have been identified. From the broadband excitation and emission spectra at RT, energy levels of the Eu3+ ion and the atomic parameters have been calculated. The D05 level of Eu3+ ions in the TZLFE glass has been selectively excited within the inhomogeneously broadened F07→D05 excitation spectrum at 15K. The resulting D05→F17 fluorescence spectra and the lifetimes of the D05 level have been obtained as a function of the excitation wavelength. From the FLN spectra, three Stark levels have been identified and crystal-field (CF) analysis has been carried out to calculate second rank CF parameters, by assuming C2v orthorhombic symmetry, as a function of the excitation wav...

Optical spectroscopy and energy transfer in Tm3+-doped metaphosphate laser glasses

Thulium-doped metaphosphate glasses with four concentrations (0.01, 0.1, 1.0 and 2.0 mol%) of Tm 3+ have been prepared and investigated by Raman, absorption and photoluminescence spectral studies. The phonon sideband spectrum has been measured for 1.0 mol% Eu 3+ -doped metaphosphate glass of the same composition and compared with the Raman spectrum. From vibronic spectra, various bands associated with different structural groups have been identified and assigned. Absorption band positions have been used to simulate the complete energ yl evel diagram for the Tm 3+ ion using the model Hamiltonian. Judd–Ofelt parameters have been determined from the absorption bands .U sing these parameters, transition probabilities, excited state lifetimes and transition branching ratios have been evaluated. The emission and decay curves of the 1 D2 level have been measured for all four glass samples both at RT and 15 K. Lifetimes show a strong quenching for Tm 3+ concentrations higher than 0.1 mol%. Fluorescence decay curves of the 1 D2 level have been well fitted to th eI nokuti–Hirayama model for S = 6, suggesting that the mechanism for energy transfer between Tm 3+ ions is of dipole–dipole type.

Yellow-to-violet, blue, and green frequency upconversions in Nd3+-doped PbWO4 single crystal

Upconversion emission properties of Nd3+ ions doped in PbWO4 crystal are investigated by pulsed laser excitation into the G5∕24+G2(1)7∕2 levels at temperatures from 10to295K. The main upconversion emission consists of strong blue emission bands in the wavelength region of 435–447nm corresponding to the P1∕22→I9∕24 transitions. Some UV bands located in the wavelength region of 356–397nm corresponding to the D3∕24→I9∕24, I11∕24, and I13∕24 transitions and weak green emission at 525.2nm corresponding to the G7∕24→I9∕24 transition are observed. Several upconversion blue emissions from the P1∕22 level and the absoprtion lines due to the I9∕24→P1∕22 transition indicate multisite structure of the Nd3+ ions in the PbWO4 lattices. We investigate the excitation spectra of the upconversion emissions and their pump power dependence and lifetimes from which the probable upconversion mechanisms are proposed and analyzed. The dominant mechanisms for the upconversion emission originating from the D3∕24 level (UV emission...

Synthesis and Luminescence Properties of Tb 3+ -Doped K 2 BaW 2 O 8 Phosphors

Abstract Green phosphors K 2 BaW 2 O 8 :Tb 3+ (1.0 mol%) were synthesized by solid state reaction method. Differential thermalanalysis was applied to trace the reaction processes. Three endothermic values of 95, 706, and 1055 o C correspond to the lossof absorbed water, the release of carbon dioxide, and the beginning of the melting point, respectively. The phase purity of thepowders was examined using powder X-ray diffraction(XRD). Two strong excitation bands in the wavelength region of 200-310 nm were found to be due to the WO 42− exciton transition and the 4f-5d transition of Tb 3+ in K 2 BaW 2 O 8 . The excitationspectrum presents several lines in the range of 310-380 nm; these are assigned to the 4f-4f transitions of the Tb 3+ ion. The strongemission line at around 550 nm, due to the 5 D 4 → 7 F 5 transition, is observed together with weak lines of the 5 D 4 → 7 F J (J = 3,4, and 6) transitions. A broad emission band peaking at 530 nm is observed at 10 K, while it disappears at room temperature.The decay times of Tb