PL Emission Bands Research Articles

Synthesis and photoluminescence study of Dy3+ activated SrAl12O19 phosphor

Dy3+ doped SrAl12O19 phosphors, capable of radiating white light, were successfully synthesized via combustion method. Phase identification, morphological observations and elemental examination were done by employing X-ray diffraction, Field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The peaks in the X-ray diffraction patterns are found to be indexed well with the hexagonal phase (JCPDS card number 80-1195). Under 350 nm of excitation wavelength, the PL emission bands were peaking at 478 nm and 573 nm, which can be ascribed to the intra-4f transition of Dy3+. The emission data were analyzed for determining the CIE chromaticity coordinates and the correlated color temperature (CCT). A cool white light with chromaticity coordinates x = 0.3098 and y = 0.3538 and correlated color temperature of 6542 K was achieved for 3 mol% at 350 nm excitation. These results indicate that SrAl12O19:Dy3+ have practical applications in UV-pumped white light emitting diodes.

Photoluminescence properties of Er3+/Yb3+ doped ZrO2 coatings formed by plasma electrolytic oxidation

In the present work, down- and up-conversion photoluminescence properties of Er3+/Yb3+ doped ZrO2 coatings formed by plasma electrolytic oxidation of zirconium in electrolyte containing Er2O3 and Yb2O3 particles were investigated. Down-conversion PL analysis shows that emission spectra of ZrO2:Er3+/Yb3+ coatings excited with 280 nm radiation are composed of broad PL band related to ZrO2 host and bands assigned to f-f transitions of Er3+. The main PL emission bands of Er3+ at around 548 nm and 560 nm are related to 4S3/2→4I15/2 transition. PL excitation spectra monitored at 548 nm feature broad band in the region from 250 nm to 350 nm which is associated with the electron transfer transition from 2p orbital of O2− to 4f orbital of Er3+ and transitions of ZrO2. On the other hand, bands in PL excitation spectra ranging from 350 nm to 535 nm are related to 4f transitions of the Er3+ from the ground state 4I15/2 to higher energy levels. Down-conversion PL intensity decreases with increasing concentration of Yb3+ in coating due to energy transfer from Er3+ to Yb3+. ZrO2:Er3+/Yb3+ coatings show intense green (4S3/2→4I15/2) and red (4F9/2→4I15/2) up-conversion PL emission under the excitation with a 980 nm diode laser. With increasing Yb3+ concentration red up-conversion PL intensity increases more rapidly with respect to green emission, because red up-conversion PL intensity strongly depends on Yb3+ concentration, i.e. 4F9/2 state of Er3+ is directly excited by energy transfer from excited Yb3+.

Influence of Er3+ doping concentration and temperature on upconversion photoluminescence property of NaY(WO4)2 phosphor

NaY(WO4)2: Er3+ phosphors with various doping concentrations of [Er3+]/([Er3+]+[Y3+]) (0, 5, 7, 10, 12, 15%) were successfully synthesized by high-temperature solid-state reaction. X-ray diffraction (XRD) measurement demonstrated the presence of tetragonal-phase NaY(WO4)2 phosphors and Fourier transform infrared (FT-IR) spectra showed a strong υ3 stretching vibration mode of WO42−, indicating the good crystallization of the phosphors. Well-crystallized phosphors showed a fine morphology with particle sizes of 0.8–10 µm by scanning electron microscope (SEM). Under excitation of 980 nm laser, Er3+-doped phosphors exhibited strong green emissions centered at 527 and 549 nm in addition to a 665 nm emission band in the red region, which were assigned to the 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively. When the doping concentration was 10%, the intensities of green and red emissions reached their maximum values, stronger than that in 5% Er3+ doped one by 13 times. The double-logarithm plot of the upconversion (UC) emission intensity to the excitation power for different Er3+ doping concentrations depicted that at least two infrared photons were involved for every emitted green and red photon. UC emission intensity changing with temperature displayed different trends for the phosphors with different Er3+ concentrations. The enhancement for green emission band centered on 549 nm could reach 50 times at 30 K in sample with 5% Er3+ concentration. Under excitation by 355 nm laser, all the phosphors showed a strong PL emission band at 430 nm, while green luminescence band locating from 540 to 570 nm was only observed in 7, 10, and 12% Er3+-doped phosphors, which was ascribed to 4S3/2 → 4I15/2 transition.

Interfacial ferromagnetism in reduced graphene oxide–ZnO nanocomposites

Reduced Graphene Oxide (rGO) and rGO–ZnO nanocomposites have been successfully prepared by hydrothermal and solvothermal method, respectively. Powder XRD and Raman spectroscopy studies confirmed the formation of nanocomposites. The nanostructures of samples were imaged and found that ZnO nanoparticles covered over rGO sheets. The reduction of various oxygen containing functional groups attached on the few layered graphitic planes and the presence of oxygen vacancies in nanocomposites were confirmed by XPS. The relative contribution of PL emission bands in composites arises due to the existence of intrinsic defects. The M–H curve of rGO sheets and rGO–ZnO nanocomposites exhibit ferromagnetic behavior. The decrease of magnetization in composites owing to increases the rGO ratio leads to decrease the oxygen vacancies in the surface of ZnO nanopaticles.

Determination of GaAs zinc blende/wurtzite band offsets utilizing GaAs nanowires with an axial GaAsSb insert

By applying a correlated micro-photoluminescence spectroscopy and transmission electron microscopy (TEM) approach, we have utilized molecular beam epitaxy grown self-catalysed GaAs nanowires (NWs) with an axial GaAsSb insert to determine the band offsets at the crystal phase heterojunction between zinc blende (ZB) and wurtzite (WZ) GaAs. Two distinct PL emission bands originating from the ZB GaAsSb insert were identified. The lower energy PL emission allowed an independent verification of the maximum Sb molar fraction to be ∼30%, in agreement with quantitative high-angle annular dark field scanning TEM performed on the same single NW. The higher energy PL emission revealed a low temperature ZB/WZ band offset of 120 meV at the interface between the two GaAs crystal phases occurring at the upper boundary of the insert. Separate conduction and valence band offsets develop at a higher temperature due to the different temperature dependence of the ZB and WZ GaAs band gaps, but both offset values show a relatively little variation in the range of 10–150 K.

Rietveld refinement, micro-structural, optical and thermal parameters of zirconium titanate composites

Pure titania and zirconium titanate composites have been synthesized using sol-gel technique and annealed at 650, 875 and 1100°C for 4h. Acetylacetone was used to control the rate of hydrolysis of precursors. The Rietveld refinement, micro-structural, optical and thermal parameters of prepared composites was investigated. Effect of annealing and concentration of Zr and Ti in composites on their crystal structure, morphology, PL emission wavelength and band gap have been studied. X-ray diffraction and Rietveld analysis exhibit that all prepared samples of composites have orthorhombic single phase of zirconium titanate with space group pbcn. The lower values of profile parameters such as Rp, Rwp, RB, RF, χ2 indicated that the calculated diffraction pattern is in fair agreement with observed pattern. The increase in zirconia concentration decreases the degree of crystallization of ZrTiO4. The photoluminescence spectra show the blue shifting of emission peak at 420nm as the zirconia concentration increases. The optical band gap of zirconium titanate composites also blue shifted (3.24–3.64eV) with decrease in crystallite size of composites.

Radio-photoluminescence in non-doped K2CO3 ceramics

In this letter, we report a discovery of a new radio-photoluminescence (RPL) material. The RPL appeared in vacuum-sintered non-doped K2CO3 ceramics as an evolution of PL emission band peaking at 440nm. The RPL signal was confirmed to be sensitive to X-rays and stable at room temperature. The RPL response was observed as low as 1mGy although the sample was not optimized. We strongly believe that this material should be a promising candidate as RPL dosimeter materials.

High pressure induced phase transformation through continuous topology evolution in zinc hydroxyfluoride synthesized via a hydrothermal strategy

Orthorhombic ZnOHF is synthesized via a hydrothermal strategy. Powder X-ray diffraction studies confirm that the prepared samples have a diaspore-type structure. According to the EDS analysis, the O/F ratio in equimolar proportion indicates the nearly perfect stoichiometry. The morphological features observed via SEM and TEM techniques reveal that the product is composed of micro/nanometer-scaled prism-like structures. The band gap estimated from UV–vis absorption measurements is 3.15 eV. The PL emission band is located at 470 nm. The compression behaviors of the as-prepared ZnOHF samples are investigated by using in situ high pressure angle dispersive synchrotron radiation X-ray diffraction techniques. The compression behaviors are characteristic of continuous topology evolution. The pressure-induced shearing reduces the symmetry of ZnOHF from the initial space group Pnma to its subgroup Pna21 in the pressure range of 14.2–19.8 GPa. The hints of a further phase transformation to the CdOHF-type structure at 30.7 GPa are also observed.

Effect of an electron beam irradiation on optical and luminescence properties of LiBaAlF6 single crystals

Paper reports the effect of a 10 keV, 110 keV and 10 MeV electron beam irradiation on optical and luminescence properties of LiBaAlF6 (LBAF) single crystals at 10, 90, and 293 K. Five absorption bands at 2.0, 3.2, 4.3, 4.9 and 5.5 eV were revealed in irradiated crystals in the energy range of 1.2–9.5 eV. Several PL emission bands (1.7–1.8, 2.2 and 2.5–3.5 eV) related to defects were found in the luminescence spectra at room temperature, while only one luminescence band at E = 2.2 eV appears at T = 90 K in LBAF crystals after a 10 MeV electron bombardment. The PL excitation spectra and time-response for these emission bands were studied at 10, 90, and 293 K. Thermoluminescence (TL) of irradiated crystals was studied in the temperature range of 90–740 K. New TL glow peaks at 166, 530 and 670 K were revealed and their parameters were determined. Temperature dependence of relative photoluminescence yield recorded monitoring emission at the 1.87 and 2.23 eV in the temperature range from 130 to 450 K, were fitted using five quenching processes related to TL glow peaks revealed in our research. Significant similarity in the manifestation of radiation-induced defects for LBAF and previously studied LiBaF3 single crystals is noted. The effect of an electron beam irradiation on optical and luminescence properties of LBAF single crystals and possible origin of the radiation defects were discussed.

Photoluminescent colloidal Cu@C-NPs suspensions synthesized by LASL

In this work we report the synthesis of photoluminescent carbon-coated copper nanoparticles (Cu@C-NPs) based colloidal suspensions, using the laser ablation of solids in liquids technique (LASL). LASL experiments were carried out by ablating a Cu solid target immersed in acetone as the liquid medium with ns-laser pulses (1064nm) of a Nd-YAG laser. In all experiments the per pulse laser fluence and the repetition rate frequency were kept constant and the ablation time was varied. The as obtained Cu@C-NPs suspensions were optically characterized with absorption and photoluminescence spectroscopies. Raman spectroscopy was used to give evidence of the carbon shell deposited around the Cu NPs. TEM results showed that 10nm spheroids Cu@C-NPs were obtained. The as obtained Cu@C-NPs suspensions displayed out a PL emission band similar to that for carbon nanoparticles suspensions obtained by the same technique. We have found that the blue-green PL emission band intensity is mainly dependent on the ablation and aging time of the samples. The Cu@C-NPs-based colloidal suspensions can be proposed as multifunctional due to its absorbance and emission properties.

Optical and reliability properties studies of green YAG phosphors by Ga substitution

In this paper, green Y2.94(Al1−xGax)5O12:0.06Ce phosphors were prepared by conventional solid-state reaction. The crystal structures, the influence of Ga concentration on the photoluminescence, thermal stability and reliability properties of the phosphors were studied. The PL emission bands of Y2.94(Al1−xGax)5O12:0.06Ce showed blue shift from 545 nm to 525 nm with increasing Ga content (x value) under excited at 460 nm. The thermal stability of Y2.94(Al1−xGax)5O12:0.06Ce phosphor is hindered by adding Ga. As the temperature increases from 300 to 500 K, the PL intensity of Y2.94(Al0.8Ga0.2)5O12:0.06Ce and Y2.94(Al0.65Ga0.35)5O12: 0.06Ce phosphor decreases by 11.11 and 16.57 %, respectively. Reliability test results show that the relative PL intensity of Y2.94(Al1−xGax)5O12:0.06Ce phosphor decrease to from 99.76 to 95.37 % with x value increased from 0.15 to 0.35 after the ambient condition of 85 °C/RH 85 % for the exposure time of 168 h. And the relative PL intensity of Y2.94(Al1−xGax)5O12:0.06Ce phosphor decrease to from 99.53 to 91.78 % after soaking into boiled water for 4 h. It can be summarized that the addition of Ga deteriorates the thermal stability as well as the reliability of the phosphors slightly.

Photoluminescence of monoclinic Li3AlF6 crystals under vacuum ultraviolet and soft X-ray excitations

Using Bridgman technique we have grown monoclinic β-LiAF crystals suitable for optical studies, performed XRD-identification and Rietveld refinement of the crystal structure and carried out a photoluminescence study upon vacuum ultraviolet (VUV) and extreme ultraviolet (XUV)-excitations, using the low-temperature (T=7.2K) time-resolved VUV-spectroscopy technique. The intrinsic PL emission band at 340–350nm has been identified as due to radiative recombination of self-trapped excitons. The electronic structure parameters were determined: bandgap Eg≈12.5eV, energy threshold for creation of unrelaxed excitons 11.8eV<En<12.5eV. The PL emission bands at 320–325 and 450nm were attributed to luminescence caused by lattice defects. We have discovered an efficient excitation of PL emission bands in the energy range of interband transitions (Eex>13.5eV), as well as in the energy range of core transitions at 130eV. We have revealed UV–VUV PL emission bands at 170 and 208nm due to defects. A reasonable assumptions about the origin of the UV–VUV bands were discussed.

Luminescence properties of Dy3+ doped zinc–aluminum–sodium–phosphate (ZANP) glasses for white light applications

The structural and optical properties of trivalent dysprosium (Dy3+)-doped zinc– aluminum–sodium–phosphate (ZANP) glasses have been investigated using XRD, FTIR, absorption, emission spectra and decay curve. The XRD profiles and SEM images confirm the glassy nature of the investigated glass samples. FTIR spectra reveal the presence of PO4 units along with OH− groups in the glasses. The absorption spectra of Dy3+ showed eight absorption bands with hypersensitive at 1272nm (6H15/2→6F11/2) and three PL emission bands at 485nm (4F9/2→6H15/2), 576nm, (4F9/2→6H13/2) and 665nm (4F9/2→6F11/2). The luminescence intensity ratio of 4F9/2→6H13/2 to 4F9/2→6H15/2 transitions of Dy3+ in ZANP glasses gives feasibility of extracting white light. The experimental branching ratios and stimulated emission cross-sections are higher for 4F9/2→6H13/2 transition. The lifetime of the decay is obtained by taking the first e-folding times of the decay curves and is found to decrease with increase of Dy3+ ions concentration. The decay curves are found to be perfectly single exponential for samples upto1.5mol% Dy3+ ion concentrations. The non-exponential curve is obtained at 2.0mol% of Dy3+ ion concentration, which indicates the energy transfer between the donor and acceptor.

Structural, optical and electrical characterization of nanostructured porous silicon: Effect of current density

In this work, an attempt has been made to fabricate porous silicon (PS) from p-type crystalline silicon (c-Si) wafers by using the electrochemical etching process at six different current densities (40, 60, 75, 100, 125 and 150mA/cm2) with constant time (30min). The influence of varying current density on morphological, structural, optical and electrical properties of PS samples were analyzed by using SEM, AFM, XRD, FT-IR, PL and electrical (I–V) techniques, respectively. Microstructural images clearly showed that the average pore diameter and thickness increase with increase current densities up to 100mA/cm2 and decrease for 125mA/cm2. It could be related to breaking of pore walls and exposing to the next layer of c-Si. Further increase the current density about 150mA/cm2, the average pore diameter increase as in the case of first layer (40–100mA/cm2) of c-Si wafer. The result is reflected in PL emission band (at 708nm) and the intensity of the emission band shifted towards red region. The X-ray diffraction pattern confirm the formation of porous silicon as appeared as a broad peak at 2θ=69.3° belongs to (400) reflection. The FTIR study supports the X-ray diffraction analysis that shows the vibrational bands of S–H2 and Si–O–Si at 2109cm−1, 915cm−1 and 615cm−1 and 1107cm−1, respectively. The I–V characteristic of PS exhibited rectifying behavior with different values of ideality factor (η) and barrier height (ϕb). It is concluded from the experimental results that the formed pores developed up to 100mA/cm2 in the top layer of c-Si and the formed pores exposed to the next layer of c-Si when increase the high electrochemical etching process (above 100mA/cm2).

Two Structure Types Based on Si6O15 Rings: Synthesis and Structural and Spectroscopic Characterisation of Cs1.86K1.14DySi6O15 and Cs1.6K1.4SmSi6O15

AbstractThe silicate Cs1.86K1.14DySi6O15 represents a mixed tetrahedral‐octahedral framework structure type based on roughly circular Si6O15 rings and isolated DyO6 octahedra. The silicate Cs1.6K1.4SmSi6O15 has a layered atomic arrangement built from corrugated Si6O15 layers containing four‐, six‐ and eight‐membered rings. The layers are connected by isolated SmO6 octahedra to form a mixed tetrahedral‐octahedral framework. This structure shows a close structural relationship to β‐K3NdSi6O15 and a less close one to dehydrated elpidite (Na2ZrSi6O15). In both structures, Cs/K atoms occupy large voids. The silicates were obtained through high‐temperature flux syntheses. Their crystal structures have been determined from single‐crystal X‐ray diffraction data. Cs1.86K1.14DySi6O15 crystallises in R32 (no. 155) with a = 13.896(2), c = 35.623(7) Å and V = 5957.2(17) Å3, whereas Cs1.6K1.4SmSi6O15 crystallises in Cmca (no. 64) with a = 14.474(3), b = 14.718(3), c = 15.231(3) Å and V = 3244.7(11) Å3. The Dy3+ and Sm3+ cations present in the silicates cause PL emission bands in the visible yellow‐to‐orange spectral range.

Thickness dependence of structural, optical and luminescence properties of BaTiO3 thin films prepared by RF magnetron sputtering

BaTiO3 thin films were deposited onto quartz substrates by RF magnetron sputtering. X-ray diffraction pattern showed the formation of BT thin films with a tetragonal structure with orientations along (101) plane. Average crystallite size increased from 12.52 to 14.87 nm as the film thickness increased from 207 to 554 nm. With the increase in film thickness, the structural disorder decreases and the crystalline quality of the films gradually improved. The film exhibited good adherence to the substrate and are crack free. X-ray photoelectron spectroscopy revealed the presence of barium, titanium and oxygen in BT film. An average transmittance of >80 % was observed for all the films. This high transmittance BT films in the visible region is suitable for various electro-optic applications. The transmittance spectra showed high UV-shielding properties. Optical band gap was found to decrease from 4.55 to 3.70 eV with increase of film thickness, whereas the refractive index was found to increase. The refractive index of the BT films can be tuned between 2.11 and 2.21 at 550 nm. The real and imaginary dielectric constants with increase in film thickness were investigated. The low dissipation factor of BT thin films makes it a promising material for frequency agile applications. The emission spectra of BT thin films consist of near band edge excitonic UV emission and defect related emission in the visible range. The PL emission bands in UV and visible region of BT thin films make them suitable for electro-optic devices and light emitters.

Nd2O3: novel synthesis and characterization

The present work was focused on producing sustainable Nd2O3 nanoparticles for inhibiting human breast cancer cells. Novel synthesis route was described. Raman, PL, XRD, FTIR, XPS and TEM characterization was explored. Observed Raman Fg and Ag + Eg combination modes confirmed Nd2O3. PL emission bands around ∼352–392 nm (UV), ∼429–472 nm (blue), ∼580 nm (green) and ∼650 nm (red) further confirmed Nd2O3. Highest incubation period clearly exhibits (100) oriented strong XRD characteristic Nd2O3 peak. 413 and 630 cm−1 peaks represent IR characteristic metal–oxygen (Nd–O) vibrations. Nd3d peak shifted to higher binding energy upon increasing incubation period substantiate the presence of bigger particles due to rich Nd structure. 7 days incubation revealed agglomerated Nd2O3 particles (200 nm). 1 day incubated 500 (µg/ml) Nd2O3 dosage could be used as an effective biocompatibility material.

Template-free synthesis of α-GaOOH hyperbranched nanoarchitectures via crystal splitting and their optical properties

In this paper, a facile, template-free, one-step solvothermal method to synthesize size- and shape-controllable α-GaOOH with hierarchical nanoarchitectures has been developed. Hyperbranched α-GaOOH nanocrystals with a sheaf-like morphology has been prepared via the alcoholysis process with GaCl3 and methanol as the reactants in the presence of benzene as solvent at 160 °C within an autoclave. For the formation of α-GaOOH hierarchical nanoarchitectures, the crystal splitting growth mechanism plays the dominant role, which has been evidenced by the characterization of the time-dependent morphologies of the prepared samples. The UV-vis absorption spectra recorded at room temperature reveal that the obtained nanostructured α-GaOOH is a direct band gap semiconductor and the band gap Eg is estimated to be about 5.24 eV. Furthermore, a broad PL emission band can be clearly observed in the 425 to 575 nm spectrum range for the synthesized hyperbranched sheaf-like α-GaOOH nanoarchitectures.

Erbium photoluminescence response related to nanoscale heterogeneities in sol-gel silicates

Sol-gel glassy films of the SiO2-TiO2-PO2.5-ErO2.5 system containing nanocrystallites of ErPO4, were obtained through suitable heat treatments. Variations in the shape and intensity of the Er3+ photoluminescent signal around 1500 nm were linked to the nature of the host environment of the active ions; the specific features of the photoluminescent emission spectrum of the erbium 4I13/2 metastable level were interpreted in terms of structural changes in the glassy films. The photoluminescent spectrum was found to be sensitive to the order (crystalline) or disorder (amorphous) of the Er3+ ions neighbour within the glassy matrix. An amorphous environment led to a broadening of Er3+ PL emission band while a crystalline one was responsible for a drastic photoluminescent bandwidth narrowing. The presence of nanoscale heterogeneities caused a drastic photoluminescence intensity decrease. Changes in the shape of the decay curve of fluorescence lifetime were found also structurally dependent on volumetric defects, occurrence of phase separation and Er3+-Er3+ clustering effects as well.

Optical properties of lithium magnesium borate glasses doped with Dy3+ and Sm3+ ions

Several studies showed the interesting properties of trivalent lanthanide ions when doped in various types of glasses. Optical and physical properties of lithium magnesium borate glasses doped with Dy3+ then with Sm3+ ions were determined by measuring their absorption and luminescence spectra in the visible region. The absorption spectra of Dy3+ showed eight absorption bands with hypersensitive transition at 1265nm (6H15/2→6F11/2-6H9/2) and three PL emission bands at 588nm (4F9/2→6H15/2), 660nm (4F9/2→6H13/2) and 775nm (4F9/2→6H11/2). Regarding the Sm3+, nine absorption bands were observed with hypersensitive transition at 1237nm (6H5/2–6F7/2); the PL spectrum showed four prominent peaks at 4G5/2→6H5/2 (yellow color), 4G5/2→6H7/2 (bright orange color), 4G5/2→6H9/2 (orange reddish color) and 4G5/2→6H11/2 (red color), respectively. Finally, a series of physical parameters such as the oscillator strengths, refractive index, ions concentration, Polaron radius and other parameters were calculated for each dopant.