Eunjin Cho

Spectroscopic properties and Judd-Ofelt analysis of Sm3+ doped lead-germanate-tellurite glasses

Spectroscopic properties of Sm3+ (1 mol%) ions in 49 PbO–30 GeO2–20 TeO2 glass have been characterized through optical absorption and temperature dependent fluorescence. The spectroscopic parameters such as oscillator strengths (f), Judd–Ofelt (J–O) intensity parameters (Ωλ), spontaneous emission probability (AR), branching ratios (βR) and radiative lifetimes (τR) of various excited levels have been determined from the absorption spectrum by using J–O analysis. From the fluorescence spectra, four emission transitions have been observed from the 4 G5/2 state to the lower lying states 6H5/2, 6H7/2, 6H9/2 and 6H11/2 upon exciting the sample with a 488 nm line of an argon ion laser. The stimulated emission cross-sections (σe) and branching ratios (βmeas) were estimated from the emission spectra for all emission transitions and decay curve analysis for the 4G5/2 level has also been carried out for different concentrations. Based on these results, the utility of Sm3+ doped lead–germanate–tellurite glasses as laser active materials in the visible region is discussed.

Luminescence properties of triple phosphate Ca8MgGd(PO4)7 : Eu2+ for white light-emitting diodes

A novel Eu2+ ion doped triple phosphate Ca8MgGd(PO4)7 was synthesized by a general high-temperature solid-state reaction in a reductive atmosphere. X-ray powder diffraction analysis confirmed the formation of single phase Ca8MgGd(PO4)7. Scanning electron microscopy indicated that the microstructure of the phosphor consisted of irregular fine grains with a size of about 1–2 µm. Photoluminescence excitation spectrum measurements show that the phosphor can be efficiently excited by UV–visible light from 250 to 480 nm to realize emission in the visible range. The emission spectrum showed a broad and asymmetric profile from 410 to 750 nm, which corresponds to the allowed f–d transition from three kinds of Eu2+ ions. The characteristics indicated that this phosphor is a candidate for application in the white light-emitting diodes. The luminescence mechanism and three site occupancies of Eu2+ ions in Ca8MgGd(PO4)7 lattices are briefly discussed.

Synthesis, vacuum ultraviolet and ultraviolet spectroscopy of Ce3+ ion doped olgite Na(Sr, Ba)PO4

Ce3+ ion doped olgite mineral samples, Na(Sr, Ba)PO4, were prepared by a high temperature solid-state reaction. The sample was investigated through x-ray powder diffraction, FT-IR and FT-Raman spectra measurements. The optical properties under vacuum ultraviolet (VUV) synchrotron radiation and ultraviolet (UV) irradiation are reported for the first time. The investigated samples show a strong absorption in the VUV and UV ranges. The bands corresponding to the 4f1 → 4f05d1 transitions of Ce3+ ions in the host lattices are identified. The barycentre of Ce3+ ions in the host lattices, the host absorption, the crystal field splitting, the emission and the Stokes shifts are presented and discussed. This Ce3+ ion doped material is a potential candidate for plasma display panel (PDP) application.

Luminescence and microstructure of Sm2+ ions reduced by x-ray irradiation in Li2O–SrO–B2O3 glass

Sm3+-doped Li2O–SrO–B2O3 glass sample was prepared by the conventional melt quenching method in air atmosphere. Sm2+ ions in this borate glass were obtained by x-ray irradiation reduction method. The as-prepared and x-ray-irradiated samples were investigated by photoluminescence spectrum and decay curve measurements. The dependence of Sm2+ luminescence intensity on the x-ray irradiation time was investigated. It is found that the conversion of Sm3+→Sm2+ after x-ray irradiation is efficient in this borate glass. Photostability of Sm2+ ions was evaluated by the photobleaching method. Furthermore, the induced optical absorption spectrum measurement after x-ray irradiation was performed. Thermoluminescence above room temperature was also studied after x-ray irradiation. The different kinds of defect structures and the reduction mechanism of Sm2+ ions in this borate glass were discussed. The microstructure of Sm ions in the Li2O–SrO–B2O3 glass was suggested. The proposed microstructure would be helpful to unde...

Spectroscopic and structural studies of Sm2+ doped orthophosphate KSrPO4 crystal

Sm2+ ions doped KSrPO4 were prepared by high-temperature solid-state reaction method. The samples were investigated by x-ray powder diffraction, photoluminescence excitation and emission spectra, and luminescence decay measurements. After excitation into the 4f55d1 levels, the emission of Sm2+ ions showed D05→FJ7 (J=0,1,2) emission together with the broad 5d→4f emission band. The luminescence of Sm2+ ions was sensitive to the temperature. With the decreasing of the temperature, the broad 5d→4f emission band of Sm2+ ions gradually quenched, while D05→FJ7 (J=0,1,2) emission lines could be clearly detectable. Based on the luminescence properties of Sm2+ ions and structure of KSrPO4 crystal, the crystallographic sites and the energy structure correlated with 4f→5d transitions of Sm2+ ions in KSrPO4 were discussed.

SiO2 effect on spectral and colorimetric properties of europium doped SrO2–MgO–xSiO2 (0.8 ⩽ x ⩽ 1.6) phosphor for white LEDs

Silicate phosphors with compositions 1.99 SrO2–1.0 MgO–xSiO2–0.01 Eu2O3 (x = 0.8, 1.0, 1.2, 1.4 and 1.6) were prepared in a reducing atmosphere via a solid state reaction. The resultant phosphors were examined by using x-ray diffraction and confirmed to be a mixture of monoclinic Sr2SiO4 and orthorhombic Mg2(Si2O4). The scanning electron microscope images revealed that SiO2 content does not influence the morphology of the resultant phosphors. It was also observed that the excitation spectra are dependent on the monitored emission wavelength, and the emission spectra are dependent on the excitation wavelength and the SiO2 content. The energy transfer between Eu2+ ions occupying different Sr2+ sites was discussed. The colour coordinates for these phosphors are tunable based on both the excitation wavelength and the SiO2 content.

The influence of metal aluminium on the reduction of the Sm3+ doped in aluminosilicate glass films

Sm3+-doped glass sol was prepared by a sol–gel method and coated on a bare Si substrate and an Al coated Si substrate (Al/Si). The coated glass films were heat treated in a hydrogen atmosphere or air to reduce the Sm3+ to Sm2+ and then the optical properties were examined through a photoluminescence (PL) experiment. While the glass films coated on a bare Si substrate or an Al/Si one were well reduced in hydrogen atmosphere, only the glass films coated on the Al/Si substrate were reduced in air. We thus suggest two possible reducing mechanisms related to hydrogen and the metal aluminium and we found that the metal aluminium coated on a Si substrate plays an important role in the reducing process.

A blue luminescence glass-ceramics of Eu2+ ions activated Li2O-BaO-B2O3

Abstract New blue luminescence glass-ceramic samples were prepared in air by annealing of the Eu 3+ -doped Li 2 O-BaO-B 2 O 3 glass. The as-made glass samples only showed the sharp emission peaks assigned to the transitions of 5 D 0 – 7 F J ( J =0, 1, 2, 3, 4) of Eu 3+ ions. The glass-ceramic samples gave a strong and broad emission band peaking at about 382 nm ascribed to the 5d-4f transition of Eu 2+ ions. The optical properties such as excitation and emission spectra, and the decay time of the Eu 2+ ions were investigated in the glasses or the glass-ceramics samples. The X-ray diffraction pattern showed that LiBaB 9 O 15 might be demonstrated to be the crystallites in the glass-ceramic, which contributed to the blue luminescence. SEM micrograph was investigated on the glass-ceramic samples obtained by crystallization of the glass matrix resulting in a mixture of poly-crystals.