Kiwan Jang

White light generation from Dy3+-doped ZnO-B2O3-P2O5 glasses

Dysprosium doped ZnO–B2O3–P2O5 (ZBP) glasses were prepared by a conventional melt quenching technique in order to study the luminescent properties and their utility for white light emitting diodes (LEDs). X-ray diffraction spectra revealed the amorphous nature of the glass sample. The present glasses were characterized by infrared and Raman spectra to evaluate the vibrational features of the samples. The emission and excitation spectra were reported for the ZBP glasses. Strong blue (484 nm) and yellow (574 nm) emission bands were observed upon various excitations. These two emissions correspond to the F49/2→H615/2 and F49/2→H613/2 transitions of Dy3+ ions, respectively. Combination of these blue and yellow bands gives white light to the naked eye. First time, it was found that ZnO–B2O3–P2O5 glasses efficiently emit white light under 400 and 454 nm excitations, which are nearly match with the emissions of commercial GaN blue LEDs and InGaN LED, respectively. CIE chromaticity coordinates also calculated for...

Crystal structure, electronic structure, and optical and photoluminescence properties of Eu(III) ion-doped Lu6Mo(W)O12.

Lu(6)WO(12) and Lu(6)MoO(12) doped with Eu(3+) ions have been prepared by using a citrate complexation route, followed by calcination at different temperatures. The morphology, structure, and optical and photoluminescence properties of the compounds were studied as a function of calcination temperature. Both compositions undergo transitions from a cubic to a hexagonal phase when the calcination temperature increases. All the compositions have strong absorption of near-UV light and show intense red luminescence under a near-UV excitation, which is related to the transfer of energy from the host lattices to dopant Eu(3+) ions. Density functional theory calculations have also been performed. The calculation reveals that hexagonal Lu(6)WO(12) and Lu(6)MoO(12) are indirect bandgap materials, and the near-UV excitations are due to the electronic transitions from the O-2p orbitals to W-5d and Mo-4d orbitals, respectively. The lattice parameters and bandgap energies of hexagonal Lu(6)WO(12) and Lu(6)MoO(12) were determined.

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.

Thermal, structural and optical properties of Eu3+-doped zinc-tellurite glasses

Europium doped zinc-tellurite glasses modified with LiF, Na2 O+L i 2O and Na2 O+L i2 O+N b 2O5 were prepared by the conventional melting procedure and their thermal, structural and optical properties were investigated. Differential thermal analysis curves in the temperature range 30–1200 ◦ Ca t a heating rate of 10 ◦ C min −1 were used to determine the thermal properties such as glass transition, crystallization and melting temperature. FT-IR spectra were used to analyse the glass structure. The spectroscopic properties including absorption and emission spectra and fluorescence lifetime of Eu 3+ ions were measured. A strong red fluorescence is observed from the 5 D0 level of Eu 3+ ions in these glasses. The relative luminescence intensity ratio (R )o f 5 D0→ 7 F2 to 5 D0→ 7 F1 transitions has been evaluated to estimate the local site symmetry around the Eu 3+ ions. The emission spectra of these glasses show a complete removal of degeneracy for the 5 D0→ 7 F1 transition of Eu 3+ ions. Based on the energy level data obtained from the absorption and emission measurements, free-ion energy level analysis has been carried out. Second rank crystal-field parameters have been calculated together with the crystal-field strength parameter by assuming the C2v symmetry for the Eu 3+ ions in these glasses. The crystal-field parameters are found to be higher in binary zinc-tellurite glasses. The trend of variation of crystal-field strength with glass composition is found to be more or less opposite to that of R in the present glasses. The effect of temperature on the luminescence from 5 D1 level is studied. The decay from the 5 D0 level is found to be exponential and the lifetime is shorter than those found in Eu 3+ -doped borate, phosphate and fluoride based glasses.

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.

Investigation of the structure and photoluminescence properties of Eu3+ ion-activated Y6WxMo(1 − x)O12

A series of Eu3+ ion-activated Y6WxMo(1 − x)O12 polycrystalline powders were synthesized using a solid-state reaction. The crystal structure, ultraviolet-visible and photoluminescence spectra of these compounds were characterized. The structural parameters, electronic structure and orbital population of Y6WO12 and Y6MoO12 were determined by means of density functional theory calculation. The calculated structural parameters agreed well with the experimental values. Both electronic structures and ultraviolet-visible spectra indicated that the band-gap of Y6WO12 is larger than that of Y6MoO12. The WO6 or MoO6 groups in the host lattices could be efficiently excited by near-UV or violet light, and then transferred the energy to the activator Eu3+ ions, resulting in red light dominated emission. It was shown that the ratio of W to Mo in the host lattice had an impact on the luminescence intensity, the purity of the emission light and the decay lifetime strongly. Compounds Y6WxMo(1 − x)O12:Eu could be red-phosphor candidates for WLED devices.

Host sensitized novel red phosphor CaZrSi2O7 : Eu3+ for near UV and blue LED-based white LEDs

A series of red phosphors Ca1?xZrSi2O7?:?Eux (x = 0.5,1,5,10,12?mol%) were prepared by a solid-state reaction technique at various temperatures and their structural and optical properties were investigated. The x-ray diffraction profiles showed that all peaks could be attributed to the monoclinic phase CaZrSi2O7 doped with Eu3+. SEM, FTIR, TG and DTA profiles have also been characterized to explore their structural properties. The luminescence properties of these resulting phosphors have been characterized by photoluminescence spectra. The host matrix itself has shown a strong blue emission which has its maximum intensity at 470?nm. The excitation spectra of CaZrSi2O7?:?Eu3+ revealed two excitation bands at 395 and 464?nm which correspond to the sharp 7F0?5L6 and 7F0?5D2 transitions of Eu3+ and matches well with the two popular emissions from n-UV/blue GaN-based LEDs. The prominent red emission was obtained at 615?nm by the excitation transitions 5L6, 5D2 of Eu3+ through the non-radiative energy transfer process from the host to the Eu3+ ion. The effects of charge compensation by monovalent ions on the luminescence behaviour of a red emitting phosphor CaZrSi2O7?:?Eu3+ were investigated. The high colour saturation and the low thermal quenching effect of these phosphors make it a potential red component for white light emitting diodes (w-LEDs).

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.

Influence of ligands on the photoluminescent properties of Eu3+ in europium β-diketonate/PMMA-doped systems

Abstract Three kinds of europium β-diketonates Eu(DBM) 3 , Eu(BA) 3 and Eu(TTA) 3 (DBM: Dibenzoylmethane; BA: 1-Benzoylacetone; TTA: Thenoyltrifluoroacetone) were doped in poly(methyl methacrylate) (PMMA) matrix. The doped systems were studied by using photoluminescent (PL) spectroscopy, emission decay experiments and X-ray diffractometry. Eu(III) ions in the doped Eu(DBM) 3 /PMMA systems have two distinct symmetric sites and the emission band changes greatly with the compositions. Eu(III) in the Eu(BA) 3 /PMMA systems gives only one symmetric site in the doped systems and the emission band changes slightly with the compositions. Although two distinct symmetric sites of Eu(III) can be distinguished in the doped systems of Eu(TTA) 3 /PMMA, the two sites have similar 5 D 0 lifetimes and the luminescent spectra almost do not change with the compositions. XRD reveals that crystallites were formed in the doped Eu(DBM) 3 /PMMA systems that have different crystalline structure from that of the chelate, and Eu(BA) 3 and Eu(TTA) 3 exist in amorphous state in the doped systems. The difference between the PL properties and structures of the doped systems for the three kinds of chelates should be attributed to different interactions between the chelate molecules and between the chelate and PMMA.

Wide-Band Excited Y6(WMo)0.5O12:Eu Red Phosphor for White Light Emitting Diode: Structure Evolution, Photoluminescence Properties, and Energy Transfer Mechanisms Involved

Y6(WMo)(0.5)O12 activated with Eu(3+) ions was investigated as a red-emitting conversion phosphor for white light emitting diodes (WLEDs). The phosphors were synthesized by calcining a citrate-complexation precursor at different temperatures. The photoluminescence properties of the phosphors and the energy transfer mechanisms involved were studied as a function of structure evolution. It was found that the host lattices were crystallized in a cubic or a hexagonal phase depending on the synthesis conditions. Although all the phosphors showed intensive red emission under an excitation of near-UV or blue light due to energy transfer from the host lattices to Eu(3+) ions, the photoluminescence spectra and temporal decay features were found to vary significantly with the structure and crystallinity of the host lattice. The mechanisms of the energy transfer from the host lattices to Eu(3+) ions and energy quenching among Eu(3+) ions were discussed on the basis of structure evolution of the host lattice. Phosphors calcined at 800 and 1300 °C were suggested to be promising candidates for blue and near-UV light excited WLEDs, respectively.