The effect of argon gas pressure on structural,morphological and photoluminescence properties of pulsed laser deposited KY<Subscript>3</Subscript>F<Subscript>10</Subscript>:Ho<Superscript>3+</Superscript> thin films

KY₃F₁₀:Ho³⁺ thin films were deposited by a pulsed laser deposition technique with Nd–YAG laser radiation (λ = 266 nm) on (100) silicon substrate. The XRD and FE-SEM results show improved crystalline structure for the film deposited at a pressure of 1 Torr. The AFM results show that the RMS roughness of the films increases with rise in argon gas pressure. The EDS elemental mapping shows Y-excess for all the films deposited under all pressures, and this is attributed to its higher mass and low volatility as compared to K and F. XPS analysis further confirmed Y-excess in the deposited films. Green PL emission at 540 nm was investigated at three main excitation wavelengths, namely 362, 416 and 454 nm. The PL emission peaks increase with rise in background argon gas pressure for all excitation wavelengths. The highest PL intensity occurred at excitation of 454 nm for all the thin films. In addition, faint red (near infrared) emission was observed at 750 nm for all the excitations. The green emission at 540 nm is ascribed to the ⁵F₄–⁵I₈ and ⁵S₂–⁵I₈ transitions, and the faint red emission at 750 nm is due to the ⁵F₄–⁵I₇ and ⁵S₂–⁵I₇ transitions of Ho³⁺.     

Synthesis and photoluminescence of CeO2:Eu phosphor powders

The crystalline structure and photoluminescence (PL) properties of europium-doped cerium dioxide synthesized by the solid-state reaction method were analyzed. CeO₂:Eu³⁺ phosphor powders exhibit the pure cubic fluorite phase up to 10 mol% doping concentration of Eu³⁺. With indirect excitation of CeO₂ host at 373 nm, the PL intensity quickly increases with increasing Eu³⁺ concentration, up to about 1 mol%, and then decreases indicating the concentration quenching. While with direct excitation (467 nm), much more stronger PL emissions, especially the electric dipole emission ⁵D₀-⁷F₂ at 612 nm, are observed and no concentration quenching occurs up to 10 mol% doping concentration of Eu³⁺. The nature of this behavior and the cause of the concentration quenching were discussed.     

Raman scattering and photoluminescence in sodium uranyl acetate polycrystals

A technique of probe photoluminescence and Raman spectroscopy has been developed. This technique makes it possible to detect small (10^?6 to 10^?8 g) amounts of uranyl compounds at short exposure times (1?10 s). The photoluminescence spectra of Na[UO₂CH₃(COO)₃] polycrystals recorded upon excitation by short-wavelength radiation of LEDs and lasers are found to contain equidistant bands with a shift of 854 cm^?1, which corresponds to the frequency of totally symmetric uranyl vibration also manifesting itself in Raman spectra.     

Low-temperature photoluminescence in CuIn<Subscript>5</Subscript>S<Subscript>8</Subscript> single crystals

Photoluminescence (PL) spectra of CuIn₅S₈ single crystals grown by Bridgman method have been studied in the wavelength region of 720–1020 nm and in the temperature range of 10–34 K. A broad PL band centred at 861 nm (1.44 eV) was observed at T = 10 K. Variations of emission band has been studied as a function of excitation laser intensity in the 0.5– 60.2 mW cm^?2 range. Radiative transitions from shallow donor level located at 17 meV below the bottom of the conduction band to the acceptor level located at 193 meV above the top of the valence band were suggested to be responsible for the observed PL band. An energy level diagram showing transitions in the band gap of the crystal has been presented.     

Sensitisation of erbium emission by silicon nanocrystals-doped SnO2

SnO₂ thin films undoped and doped with antimony (Sb), erbium (Er) and Si nanocrystals (Si-nc) have been grown on silicon (Si) substrate using sol-gel method. Room-temperature photoluminescence (PL) measurement of undoped SnO₂, under excitation at 280 nm, shows only one broad emission at 395 nm, which is related to oxygen vacancies. The PL of Er³⁺ ions was found to be enhanced after doping SnO₂ with Sb and Si-nc. The excitation process of Er is studied and discussed. The calculation of cross-section suggests a sensitisation of Er PL by Si-nc.     

Preparation and Photoluminescence of Sm <Superscript>3+</Superscript> Doped YAlO <Subscript>3</Subscript> Phosphor

YAlO₃: Sm³⁺ phosphor has been synthesized by the solid state reaction method with calcium flouride used as a flux. The resulting YAlO₃: Sm³⁺ phosphor was characterized by X-ray diffraction (XRD) technique, Fourier transmission infrared spectroscopy (FTIR), photoluminescence . . PL excitation spectrum was found at 254,332,380,400,407, 603 and 713 nm. Under excitation of UV(713 nm) YAlO₃: Sm³⁺ (0–3 %) broad band emission were observed from 400 to 790 nm with a maximum around 713 nm of YAlO₃ host lattice accompanied by weak emission of Sm³⁺ (⁴G_5/2 – ⁶H_5/2, ⁶H_7/2,⁶H_9/2) transitions. The results of the XRD show that obtained YAlO₃: Sm³⁺ phosphor has a orthorhombic structure. The study suggested that Sm³⁺ doped phosphors are potential luminescence material for laser diode pumping and inorganic scintillators.     

Photoluminescence of CaGa<Subscript>2</Subscript>S<Subscript>4</Subscript>:Pr Polycrystals

The photoluminescence (PL) and PL excitation spectra of CaGa₂S₄ polycrystals doped with praseodymium are studied in the regions of the activator absorption and the fundamental absorption of the host. It is found that the PL excitation spectrum consists of two regions: broadband absorption in the range of 200-380 nm corresponding to the fundamental absorption of the host and the narrow-band absorption of the dopant in the range of 430–515 nm. The luminescence spectra are different for different excitation wave-lengths, which occurs because Pr³⁺ ions substitute divalent cations occupying different crystallographic positions in the host crystal lattice.     

Photoconductive properties of some chemically deposited (Cd–Pb)s films

Films of (Cd–Pb)S have been prepared using chemical deposition in aqueous alkaline bath and their subsequent condensation on substrates. Important achievements in terms of electrical response, optical absorption and photoconductivity (PC) excitation spectra, SEM, XRD and photoluminescence (PL) studies are presented and discussed. From the photocurrent curves, the ratio I_PC (saturated photocurrent)/I_DC (dark current) was observed to be of the order of 10⁶ for the systems prepared with CdCl₂, and to be 10⁷ when doped with samarium nitrate. Values of trap depth E, lifetime and mobility are evaluated from the PC decay. Band-gaps are determined from the two spectra. Diffraction lines in XRD studies are associated to CdS and PbS, and according to SEM studies layered growth of the films takes place. PL of samarium doped (Cd–Pb)S films shows an emission peak in the green-yellow region under 365?nm excitation. The PL brightness decreases with temperature.     

Luminescence of LaBr3: Ce,Hf crystals under photon excitation in the ultraviolet,vacuum ultraviolet,and X-ray ranges

This study has been carried out using synchrotron radiation, time-resolved luminescence ultraviolet and vacuum ultraviolet spectroscopy, optical absorption spectroscopy, and thermal activation spectroscopy. It has been found that, in scintillation spectrometric crystals LaBr₃: Ce,Hf characterized by a low hygroscopicity, along with Ce³⁺ centers in regular lattice sites, there are Ce³⁺ centers located in the vicinity of the defects of the crystal structure. It has also been found that the studied crystals exhibit photoluminescence (PL) of new point defects responsible for a broad band at wavelengths of 500–600 nm in the PL spectra. The minimum energy of interband transitions in LaBr₃ is estimated as E _g ～ 6.2 eV. The effect of multiplication of electronic excitations has been observed in the range of PL excitation energies higher than 13 eV (more than 2E _g ). Thermal activation studies have revealed channels of electronic excitation energy transfer to Ce³⁺ impurity centers.     

Optical excitation and emission processes of Si-QD/SiO2 multilayer films with different SiO2 layer thicknesses

Si-rich oxide/SiO₂ multilayer films with different SiO₂ layer thicknesses have been deposited by the plasma enhanced chemical vapor deposition technique, and crystallized Si quantum dot (Si-QD)/SiO₂ multilayer films are obtained after annealing at 1100 ^°C. The photoluminescence (PL) intensity of the multilayer films increases significantly with increasing SiO₂ layer thickness, and the PL peak shifts from 1.25 eV to 1.34 eV. The PL excitation spectra indicate that the maximal PL excitation intensity is located at 4.1 eV, and an excitation–transfer mechanism exists in the excitation processes. The PL decay time for a certain wavelength is a constant when the SiO₂ thickness is larger than 2 nm, and a slow PL decay process is obtained when the SiO₂ layer is 1 nm. In addition, the PL peak shifts toward high energy with decreasing temperature only when the SiO₂ layer is thick enough. Detailed analyses show that the mechanism of PL changes from the quantum confinement effect to interface defects with decreasing SiO₂ layer thickness.     

Synthesis and characterization of fast-decaying bluish green phosphors of Tb3+-doped CaSi2O2N2 for 2D/3D plasma display panels

Oxynitride phosphor powders comprising of CaSi₂O₂N₂ doped with Tb³⁺ were successfully synthesized using a high-temperature solid-state reaction method. The experimentally determined photoluminescence (PL) properties of the produced phosphors meet the requirements of 2D/3D plasma display panels (PDPs). In particular, under the excitation of vacuum ultraviolet (VUV) synchrotron radiation and ultraviolet (UV) irradiation, emission peaks corresponding to the ⁵D₃→⁷F_J (J=6, 5, 4, 3) and ⁵D₄→⁷F_J (J=6, 5, 4, 3) transitions of Tb³⁺ ions were recorded. Monitoring the ⁵D₄→⁷F₅ emission of Tb³⁺ at 545 nm, the excitation bands were assigned to the host-related absorption as well as the 4f–5d (fd) and the 4f–4f (ff) transitions of Tb³⁺. The produced phosphors can be efficiently excited at 147 nm, and have an adequately short decay time (τ_1/10=1.14 ms).     

Synthesis and luminescent characteristics of one-dimensional europium doped Gd2O3 phosphors

One-dimensional (1D) Gd₂O₃:Eu³⁺ nano-rods and micro-rods were prepared using a facile sol-gel precipitation method, without a template and with a post-growth heat treatment in air. Based on scanning electron microscopy (SEM) and X-ray diffraction (XRD) data, hexagonal Gd(OH)₃:Eu³⁺ micro-rods, 60∼90 nm in diameter and 700 nm to 1 μm in length, were synthesized and then transformed by calcining (800°C, 2 hr) to cubic Gd₂O₃:Eu³⁺ with the same morphology and dimensions. Nano-rods of Eu³⁺ doped Gd(OH)₃ and calcined Gd₂O₃, 60∼90 nm diameter and 150∼300 nm length, were prepared by adding polyethylene glycol (PEG) as a capping agent during the sol-gel synthesis. Photoluminescence (PL) spectra exhibited the ⁵D₀–⁷F₂ transitions of Eu³⁺ at 612 and 627 nm from excitation at 280 nm. Photoluminescence excitation (PLE) data showed that a small fraction of PL from Eu³⁺ resulted from direct excitation, but most PL resulted from the oxygen to europium charge-transfer band (CTB) between 250 and 280 nm.     

Synthesis and Optical Properties of Novel Red-Emitting PbNb<Subscript>2</Subscript>O<Subscript>6</Subscript>: Eu<Superscript>3+</Superscript> Phosphors

Undoped and PbNb₂O_6:Eu³⁺ (1.0 ≤ x ≤ 6.0 mol%) phosphors were synthesized at 1100 °C for 3.5 h by the conventional solid state reaction method. Synthesized PbNb₂O₆:Eu³⁺ phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Photoluminescence (PL) analyses. The PL spectra showed series of excitation peaks between 350 and 430 nm due to the 4f–4f transitions of Eu³⁺. For 395.0 nm excitation, emission spectra of Eu³⁺ doped samples were observed at 591 nm (orange) and 614 nm (red) due to the ⁵D₀ → ⁷F₁ transitions and ⁵D₀ → ⁷F₂ transitions, respectively. PL analysis results also showed that the emission intensity increased by increasing Eu³⁺ ion content. No concentration quenching effect was observed. The CIE chromaticity color coordinates (x,y) of the PbNb₂O₆:Eu³⁺ phosphors were found to be in the red region of the chromaticity diagram.     

Study of VUV emission and γ-ray responses of Nd:BaF2 scintillaotor

Nd³⁺ 1%, 5% and 10% doped BaF₂ single crystals were grown by the micro-pulling down method. Photoluminescence properties, including excitation and emission spectra and luminescence decay were measured under synchrotron radiation excitation at the Superlumi station in HASYLAB at DESY (Hamburg, Germany). The Nd³⁺ related 5d-4f emission lines peaking around 180 nm, 230 nm, and 260 nm, identified as the 5d–⁴I_j, 5d–⁴F_j, and 5d–²G_j transitions, were observed under 140–168 nm excitation. In photoluminescence decay under the 160 nm excitation, the dominant component decay time is about 12, 2.5 and 1.2 ns for Nd³⁺ 1%, 5% and 10% concentration, respectively. The decay time shortening is explained by the concentration quenching effect. Transmittance of Nd1% sample is about 80% for wavelengths above 185 nm. Finally, gamma-ray responses, non-proportionality and energy resolution of Nd1% sample were compared with the undoped BaF₂ scintillator. The light yield of the Nd1%:BaF₂ is about 93% of that of undoped BaF₂. ^©2009 Elsevier Ltd. All rights reserved.     

Preparation and characterization of ZrO2:Sm amorphous thin films by solid state photochemical deposition method

Thin films of ZrO₂ loaded with 10, 30 and 50 mol% Sm were prepared by a photochemical method using thin films of metal acetylacetonate complexes as precursors. The photolysis of these films induces the fragmentation of the acetylacetonate ligand and the partial reduction of metal ion together with volatile organic compounds. When the metallic complex is exposed to air, the product of the reaction is metal oxide. The photoreactivity of these films was monitored by FT-IR spectroscopy, followed by a post-annealing treatment process. The obtained films were characterized by X-ray photoelectron spectroscopy and atomic force microscopy.Photoluminescense studies of the films employed 400 nm radiation for excitation of the Sm ions present. The emission spectra showed signals arising from the ⁴G_5/2→⁶H_J (J=3/2, 7/2, 9/2) transitions, where the ⁴G_5/2→⁶H_3/2 transition has the highest intensity. The concentration dependence of the PL intensity was also studied. A maximum PL intensity was observed with 10 mol% Sm content but then diminished with higher Sm concentrations.     

Correlation of photoluminescence of (Y, Ln)VO4:Eu (Ln=Gd and La) phosphors with their crystal structures

We have studied the photoluminescence (PL) of (Y, Ln)VO₄:Eu³⁺ (Ln=La and Gd) phosphors and the correlation of the PL of those phosphor with their crystal structure. It is found that (Y, Gd)VO₄:Eu³⁺ phosphors have the same crystal structure as YVO₄:Eu³⁺, which is tetragonal with a little different lattice parameters. In the case of (Y, La)VO₄:Eu³⁺ phosphors, however, the gradual change from tetragonal to monoclinic structure of host lattice was observed as the amount of La ion increased. To investigate the PL property of (Y, Ln)VO₄:Eu³⁺ (Ln=La and Gd) phosphors, vacuum ultraviolet (VUV) and ultraviolet (UV) excitation were used. The favorable crystal structure for the PL intensity of orthovanadate phosphor under 147 and 254 nm excitation was tetragonal containing Gd ion and under 365 nm excitation was monoclinic containing La ion which might have the lowest site symmetry for Eu³⁺ ion.     

Vibronic excitation spectrum of alkali aluminometaphosphate glasses containing uranium

The absorption, excitation and emission spectra of metaphosphate glasses MPO₃.Al(PO₃)₃ (M = Li, Na, K) doped with 1 or 2 w.% of uranium oxide have been measured at room temperature. The spectra were compared with those of solid uranyl nitrate and its water solution. The excitation band of glasses peaking at about 420 nm shows a great deal of structure like that of the solution. The diffuse structure would be due to the electron vibronic transitions in the uranium centre of a molecular form (probably uranyl (UO₂)²⁺).     

Electron beam induced green luminescence and degradation study of CaS:Ce nanocrystalline phosphors for FED applications

Green luminescence and degradation of Ce³⁺ doped CaS nanocrystalline phosphors were studied with a 2 keV, 10 μA electron beam in an O₂ environment. The nanophosphors were synthesized by the co-precipitation method. The samples were characterized using X-ray diffraction, Transmission electron microscopy, Scanning electron microscopy/electron dispersive X-ray spectroscopy and Photoluminescence (PL) spectroscopy. Cubic CaS with an average particle size of 42 ± 2 nm was obtained. PL emission was observed at 507 nm and a shoulder at 560 nm with an excitation wavelength of 460 nm. Auger electron spectroscopy and Cathodoluminescence (CL) were used to monitor the changes in the surface composition of the CaS:Ce³⁺ nanocrystalline phosphors during electron bombardment in an O₂ environment. The effect of different oxygen pressures ranging from 1 × 10⁻⁸ to 1 × 10⁻⁶ Torr on the CL intensity was also investigated. A CaSO₄ layer was observed on the surface after the electron beam degradation. The CL intensity was found to decrease up to 30% of its original intensity at 1 × 10⁻⁶ Torr oxygen pressure after an electron dose of 50 C/cm². The formation of oxygen defects during electron bombardment may also be responsible for the decrease in CL intensity.     

Photoluminescence properties of thenardite activated with Eu

Na₂SO₄:Eu phosphors were prepared by heating pure natural thenardite with EuF₃ at 900 °C for 20 min in air. The photoluminescence (PL) and excitation spectra of as-prepared and γ-ray-irradiated phosphors were observed at 300 K. The PL spectrum under 394 nm excitation consisted of strong narrow bands with peaks at 579, 592, 616, 652, 697 and 741 nm, assigned to the ⁵D₀→⁷F_J (J=0, 1, 2, …, 5) transitions, respectively, within Eu³⁺. The PL spectrum under 340 nm excitation consisted of a broad Eu²⁺ band with a peak at 435 nm. The excitation spectrum obtained by monitoring the violet luminescence consisted of a weak band with a peak at approximately 261 nm and a broad Eu²⁺ band with a peak at approximately 338 nm. The relative efficiency of the violet luminescence of the γ-ray-irradiated phosphor at the exposure of 46 kGy increased up to 3.0 times that of the unirradiated phosphor. The enhancement of violet luminescence by γ-ray irradiation was ascribed to the conversion of Eu³⁺ to Eu²⁺ in Na₂SO₄.     

SrAl4O7:Tm3+/Yb3+ nanocrystalline blue phosphor: structural, thermal and optical properties

Strontium aluminate (SrAl₄O₇) nanophosphor codoped with Tm³⁺–Yb³⁺ has been synthesized through the combustion route using urea as the reducing agent. Structural, thermal and optical characterizations have been carried out. Heat treatment of the samples shows a change in the crystallite phases and the relative luminescence intensities for the different bands. The nanocrystalline particles in the as-synthesized sample seem to arrange in rod like shapes of submicrometer length on annealing. A broad (350–550 nm) emission in the UV–green region is observed when 266 nm radiation is used for excitation. Intense upconversion (UC) emissions in blue, red and infrared are seen with excitation by 976 nm radiation. An emission at 364 nm not observed earlier and attributed to ¹D₂→³H₆ transition in Tm³⁺ is also seen. The blue emission from SrAl₄O₇:Tm³⁺/Yb³⁺ codoped nanophosphor (annealed at 1200°C) exhibits high color purity (89%) and is comparable to phosphors used commercially. The energy transfer mechanisms, responsible for these UC emissions, are proposed and discussed.