Yellow Emission Peak Research Articles

Synthesis and luminescence properties of Eu3+ co-doped NaBi(MoO4)2:Dy3+ phosphors for white light-emitting diodes

Dy3+-doped and Dy3+/Eu3+ co-doped NaBi(MoO4)2 phosphors were successfully synthesized using a high temperature solid-state method. The crystal structure and phase purity of these as-prepared samples were characterized by X-ray diffraction. Under 453 nm excitation, NaBi(MoO4)2:Dy3+ phosphors exhibited the characteristic weak blue emission peak at 488 nm and strong yellow emission peak at 577 nm, which originate from the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions, respectively. Therefore, a white light could be composed of a blue light from chip and yellow emission of NaBi(MoO4)2:Dy3+ phosphor. Additionally, color-tunable emissions were observed in the spectra of NaBi(MoO4)2:Dy3+, Eu3+ phosphors due to efficient energy transfer from Dy3+ to Eu3+ ions. By varying co-doping concentrations of Dy3+ and Eu3+ ions, the emission color of NaBi(MoO4)2:Dy3+, Eu3+ could be varied for high quality blue-excited white light-emitting diodes.

Luminescence properties of dysprosium doped YVO4 phosphor

Trivalent dysprosium (Dy3+) activated nanocrystalline yttrium vanadate (YVO4) phosphor was synthesized via co-precipitation method. The prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), optical absorption and photoluminescence (PL) techniques. The XRD patterns reveal the tetragonal crystalline phase. SEM images reveal that Dy doped YVO4 nanocrystals are agglomerated. EDAX confirms the formation of YVO4:Dy. FTIR spectrum shows two strong absorption bands at 459 and 761 cm−1. Optical absorption spectrum showed the surface defects in the as-prepared samples. The PL emission spectrum shows two characteristic emission bands at 485 and 575 nm. The strong yellow emission peak at 575 nm is assigned to 4F9/2 → 6H13/2 hyper sensitive transition of Dy3+ ions. Study of CIE chromaticity diagram indicates the suitability of the phosphor for the development of yellow-green LEDs.

High temperature synthesis of yellow-emitting Y2BaAl4SiO12:Ce3+ phosphors for WLED applications

Yellow-emitting Y2BaAl4SiO12:Ce3+ (YBAS:Ce3+) phosphors were synthesized by a sol-gel method followed by annealing at high temperature. The phase purity of the YBAS:Ce3+ phosphors was confirmed by X-ray diffraction analysis. The emission characteristics of YBAS:Ce3+ phosphors were investigated by measuring their photoluminescence excitation and emission spectra. These phosphors can be efficiently excited with blue light that induced an intense yellow emission peak centered at 530 nm. White light-emitting diodes (WLEDs) were fabricated using the synthesized YBAS:6Ce3+ phosphors. The CIE chromaticity coordinates of YBAS:6Ce3+ and the fabricated WLEDs were located at the yellow (0.391, 0.563) and cool white-light (0.265, 0.326) regions, respectively.

E. tirucalli plant latex mediated green combustion synthesis of ZnO nanoparticles: Structure, photoluminescence and photo-catalytic activities

Abstract ZnO nanoparticles were synthesized using esterases contained E. tirucalli plant latex as a fuel. The structural, morphological and spectroscopic studies of the as-synthesized ZnO nanoparticles were analyzed using powder X-ray Diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), UV–Visible absorption and photoluminescence (PL) spectroscopy. The structural parameters were refined by the Rietveld refinement method using PXRD data and confirmed that the prepared compound is pure hexagonal wurtzite structure with space group P63mc (No. 186). The average crystallite size was estimated by Scherrer's and W H plots and found to be in the range 17–23 and 20–26 nm respectively. The band gap of ZnO nanoparticles was estimated using Wood–Tauc relation and found to be in the range of 3.10–3.25 eV. PL studies revealed that a broad yellow emission peak appeared at 570 nm upon 380 nm excitation peaks. Photocatalytic degradation of Methylene blue (MB) dye was studied under UV irradiations. 5.5 ml of 5% esterases contained E. tirucalli plant latex used for the synthesis of ZnO shows 96% of degradation (5 × 10−5 M MB at pH 12). The prepared ZnO nanoparticles find application in optical and photo-catalytic degradations.

Preparation and luminescent properties of new YAG:Ce3+ phosphor in glass (PIG) for white LED applications

A yellow-emitting phosphor-in-glass (PIG) material was synthesized by dispersing commercial YAG:Ce3+ phosphor powder in homemade host glass prepared by melting-quenching method. The phase composition, microstructure and photoluminescence properties of PIG were investigated by means of XRD, SEM, fluorescence spectrophotometer and optoelectronic testing system. The results showed that the YAG:Ce3+ phosphor particles were uniformly distributed and well preserved in glass matrix without any decomposition reaction. The bulk PIG can be efficiently exited by 460 nm to emit a broad yellow emission peak (530 nm) attributed to 5d → 4f transition of Ce3+ ion. The optimal luminous property of PIG can be achieved when YAG:Ce3+ phosphor concentration, melting temperature and thickness are 8 wt%, 950 °C and 1.5 mm, respectively. Under driving current of 540 mA, the luminous efficiency of the white LED device packaged by the as-prepared PIG and blue LED chip is 98 lm/W, and its color coordinate, color temperature and color rendering index are (0.300, 0.339), 7125 K and 71, respectively. This finding shows potential applications in white LEDs for the as-prepared PIG material.

Li1.11−yTa0.89−3yTi0.11+4yO3 M-phase solid solutions: structural, dielectric and optical characterization

In this study, the structural, dielectric and photoluminescence analysis of M-phase Li1.11−yTa0.89−3yTi0.11+4yO3 (y = 0.00, 0.02, 0.07, 0.12, 0.17) solid solutions in the Li2O–Ta2O5–TiO2 ternary system prepared by conventional solid state method has been carried out. X-ray diffraction patterns revealed the formation of M-phase solid solutions with hexagonal symmetry. Superstructure formation was observed for composition y ≥ 0.07. The closely packed and plate-like grains were formed with high density (relative density > 92%) as a result of moderate sintering at 1150 °C. The average particle size 22.63 nm was obtained using Transmission electron microscopy. Dielectric permittivity decreased from 41 to 32 and temperature co-efficient of resonant frequency changed from − 106 to 43 ppm/°C with variation in y = 0.00 to 0.17 at 1 MHz frequency. The maximum value of photo-luminous intensity (287.21) was obtained for the composition Li1.11Ta0.89Ti0.11O3 that exhibits the yellow photo-luminous emission peak at 580.2 nm.

Effect of interface voids on electroluminescence colors for ZnO microdisk/p-GaN heterojunction light-emitting diodes

This study investigates the influence of voids on the electroluminescence (EL) emission color of ZnO microdisk/p-GaN heterojunction light-emitting diodes (LEDs). For this study, position-controlled microdisk arrays were fabricated on patterned p-GaN via wet chemical epitaxy of ZnO, and specifically, the use of trisodium citrate dihydrate (TCD) yielded high-density voids at the bottom of the microdisk. Greenish yellow or whitish blue EL was emitted from the microdisk LEDs formed with or without TCD, respectively, at reverse-bias voltages. Such different EL colors were found to be responsible for the relative EL intensity ratio between indigo and yellow emission peaks, which were originated from radiative recombination at p-GaN and ZnO, respectively. The relative EL intensity between dichromatic emissions is discussed in terms of (i) junction edge effect provoked by interfacial voids and (ii) electron tunneling probability depending on the depletion layer geometry.

Yellow MgV2O6·2H2O nanophosphor synthesized by a water-assisted solid-state reaction (WASSR) method at low temperature below 80 °C

Magnesium metavanadate dihydrate (MgV2O6·2H2O) was synthesized as a nanophosphor by a water-assisted solid-state reaction (WASSR) method, and its crystal structure and luminescence properties were investigated in detail. MgV2O6·2H2O has an orthorhombic structure with space group Pnma. In the crystal structure, the MgO6 octahedra and VO4 tetrahedra formed a layered structure in the direction of the b axis, and the VO4 tetrahedra formed a chain structure along the a axis. The nanophosphor showed broad and strong optical absorption in the near-ultraviolet region and exhibited a broad yellow emission peak at 563 nm.

Sol-gel-nitridation preparation and photoluminescence properties of Dy3+-doped M2Si5N8 (M=Ca, Sr, Ba) phosphors for white light emitting diodes

M2Si5N8:Dy3+(M=Ca, Sr, Ba) nitride phosphors with different Dy3+ ion concentrations were prepared via a novel sol-gel-nitridation method involving an annealing step at 1300 or 1400°C. The X-ray diffraction patterns indicate that the structure of these phosphors is in good agreement with the standard M2Si5N8 crystal structure. The photoluminescence spectra recorded for the prepared phosphors exhibited an intense white emission consisting of a blue emission peak (485nm) and a yellow emission peak (582nm), which are attributed to the characteristic 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of the Dy3+ ions, respectively. When using a different alkaline earth metal, the structure of the resulting M2Si5N8 phosphors changed and the luminescence was also affected. The chromaticity coordinates of the prepared Sr2Si5N8:Dy3+, Ca2Si5N8:Dy3+, Ba2Si5N8:Dy3+ phosphors with blue and yellow emission peaks were (x=0.391, y=0.397), (x=0.448, y=0.433) and, (x=0.42, y=0.414), respectively, which are all close to the standard white light coordinates (0.33, 0.33). The lifetime values of the obtained Ca2Si5N8:Dy3+, Sr2Si5N8:Dy3+ and Ba2Si5N8:Dy3+ phosphors were determined to be 0.028, 0.0167 and 0.0113ms, respectively.

Studies regarding ZnS:Mn nanopowders prepared from single source molecular precursor using microwave-assisted decomposition

Nanocrystalline undoped and manganese doped zinc sulphide (ZnS) powders were prepared by microwave—assisted solvothermal decomposition of zinc-manganese diethyldithiocarbamate as single-source molecular precursor. The precursors are being obtained in aqueous solution, from sodium diethyldithiocarbamate and zinc-manganese acetate mixtures containing variable amounts of manganese. Complementary investigations such as: thermal analysis, X-ray diffraction, SEM and BET were used to characterize both the precursors and phosphors. After the solvothermal treatment, the specific surface area of the powders increases from 2.04m2/g to 154.5m2/g. Phosphor samples consist of small particles (∼12nm) which present a high tendency to form spherical agglomerations. Photoluminescence spectra show a dominant yellow emission peak at 568nm accompanied by several weaker peaks. In this paper, we discuss about the manganese incorporation effect in ZnS lattice concerning the morpho-structural and luminescent characteristics of the samples.

Synthesis and luminescence properties of novel white emitting phosphor KMgLa(PO4)2:Dy3+

A series of white emitting phosphor of KMgLa (PO4)2:Dy3+ were synthesized via high temperature solid-state method, and the luminescence properties were systematically investigated. Under the 349nm ultraviolet excitation, KMgLa(PO4)2:Dy3+ shows the 481nm (blue) and 575nm (yellow) emission peaks, which are assigned to the 4F9/2–6H15/2 and 4F9/2–6H13/2 transitions of Dy3+. The emission intensities of KMgLa(PO4)2:Dy3+ are influenced by the Dy3+ concentration, and the concentration quenching effect is observed, and the corresponding mechanism is the dipole–dipole (d–d) interaction, and the critical distance is calculated to be 1.136nm. The CIE chromaticity coordinates of KMgLa(PO4)2:Dy3+ are close to that of standard white light. According to the emission intensity with different temperatures, the sample should have the good thermal stability. The results indicate that KMgLa(PO4)2:Dy3+ may be a potential application to white LEDs.

NaGdF4:Dy3+ nanofibers and nanobelts: facile construction technique, structure and bifunctionality of luminescence and enhanced paramagnetic performances.

Luminescent-magnetic bifunctional NaGdF4:Dy3+ nanofibers and nanobelts have been successfully fabricated by a combination of electrospinning followed by subsequent calcination with fluorination technology for the first time. The structure, morphologies, and luminescence and magnetic properties of the synthesized materials have been investigated by a variety of techniques. X-ray diffraction (XRD) analysis shows that as-prepared NaGdF4:Dy3+ nanostructures are pure hexagonal structures. Scanning electron microscopy (SEM) observations indicate that directly electrospinning-made PVP/[NaNO3 + Gd(NO3)3 + Dy(NO3)3] composite nanofibers and nanobelts have smooth surfaces, good dispersion and uniform size, and surfaces of NaGdF4:Dy3+ nanofibers and nanobelts become rough after calcination and fluorination processes. The mean diameters of PVP/[NaNO3 + Gd(NO3)3 + Dy(NO3)3] composite nanofibers and NaGdF4:0.5%Dy3+ nanofibers are, respectively, 402.20 ± 2.39 nm and 246.06 ± 5.84 nm at the confidence level of 95%. The mean widths and thicknesses of PVP/[NaNO3 + Gd(NO3)3 + Dy(NO3)3] composite nanobelts and NaGdF4:0.5%Dy3+ nanobelts are 4.16 ± 0.17 μm and 279 nm, and 0.83 ± 0.01 μm and 130 nm, respectively. Under the excitation of 274 nm ultraviolet light, NaGdF4:Dy3+ nanofibers and nanobelts show the predominant blue and yellow emission peaks at 478 and 570 nm corresponding to the 4F9/2 → 6HJ/2 (J = 15, 13) energy level transitions of Dy3+ ions, respectively. NaGdF4:0.5%Dy3+ nanofibers have higher photoluminescence intensity than their nanobelt counterpart. In addition, all the NaGdF4:Dy3+ nanofibers and nanobelts display superparamagnetic properties. The NaGdF4:0.5%Dy3+ nanobelts show the highest magnetization, and NaGdF4:0.5%Dy3+ nanofibers have slightly higher magnetization values than NaGdF4 nanofibers. NaGdF4:Dy3+ nanofibers and nanobelts simultaneously possess excellent luminescence and enhanced superparamagnetic properties, which make them ideally suitable for application in many fields such as solid-state lasers, lighting and displays, and magnetic resonance imaging. The design conception and construction strategy developed in this work may provide some new guidance for the synthesis of other rare earth fluoride nanostructures with various morphologies.

Investigation on the physical properties of Zn0.94Cu0.06O coated film

Abstract We report the properties of Zn 0.94 Cu 0.06 O sintered film that was prepared by screen printing technique and followed by sintering temperature at 500 °C. The sample was characterized by XRD, SEM, PL and two probe techniques. The XRD pattern of the film shows polycrystalline with wurtzite structure along the preferred orientation (1 0 1). SEM image shows porous nature with granular shape. Photoluminescence spectroscopy of the Zn 0.94 Cu 0.06 O film showed a strong emission peak at 391 nm near the band edge along with a weak green–yellow emission peak spanning the range of 450 to 600 nm. The DC conductivity measurement shows decrease in resistivity with rise in temperature having activation of energy 0.63 eV.

Self-assembled growth of tandem nanostructures based on TiO2 mesoporous/ZnO nanowire arrays and their optoelectronic and photoluminescence properties

Growth of ZnO nanowires within TiO2 mesoporous structures is carried out by hydrothermal method. Structural, optical and thermal characterizations have been carried out by SEM, XRD, EDAX, DTG, TG, PL and UV–Vis spectroscopy. XRD characterization shows that the all diffraction peaks of the tandem nanostructures films can be well indexed to a mixture of hexagonal wurtzite ZnO and anatase TiO2 structures. The UV–Visible absorbance spectrum indicates that the tandem nanostructures based on TiO2 mesoporous/ZnO nanowire arrays have 3.13 eV band gap energy while pure ZnO nanowire and bare TiO2 mesoporous show 3.37 and 3.22 eV band gap energy, respectively. The PL spectra of tandem nanostructures show that the UV, violet and yellow emission peaks appeared at 3.1, 2.6 and 2.3 eV, respectively. It has been shown that from the PL spectra, the enhanced ultraviolet emission of TiO2/ZnO tandem structures is related to the fluorescence resonance energy transfer between TiO2 mesoporous and ZnO nanowires. Thermogravimetric analysis from room temperature to 800 °C has been performed to identify the thermal stability and the amount of tandem TiO2/ZnO structures.

Synthesis Of Novel Al-doped SnO2 Nanobelts With Enhanced Ammonia Sensing Characteristics

Pure and Al-doped single-crystalline 1-D SnO2 based nanostructures were synthesized via a catalyst free simple chemical vapour transport and condensation process in Ar/O2 atmosphere. The crystalline structure, morphology and defect states of pure and Al- doped SnO2 nanostructures have been investigated in detail. Incorporation of Al in the interstitial voids of tetragonal SnO2 lattice is proved by investigating through various analytical techniques. Al doping in SnO2 significantly increases its defect concentration as demonstrated by photoluminescence spectra. The PL spectra for pure and Al-loaded SnO2 samples shows a less intense excitonic peak at ~384 nm in the UV region apart from the broad and intense yellow emission peak centred at around ~596 nm and a shallow peak at ~672 nm, respectively. For the development of stable and economically viable sensor modules for ammonia vapour detection, sensitivity at three different concentration of NH3 vapours (25ppm, 50 ppm and 100 ppm) were investigated by varying the operating temperature (250-400 °C). The minimum sensitivity for Al-doped SnO2 nanobelts was found to be 0.47 (at 25 ppm and 250 °C) and the maximum as 1.85 (at 100 ppm and 350 °C), which is 2-3 times higher than that for pure SnO2 nanowire assembles. Our results are found to be reproducible after cross examination by repeated observations. The response time (35-110 s), and recovery time (50-120 s) of our Al-doped SnO2 nanostructured sensors, for different concentrations of NH3 vapours, are equivalent or less if compared to those of available metal-oxide sensors in market. Copyright © 2015 VBRI press.

A study of the nano-structured aggregated tin oxides (SnO2/SnO) and their structural and photoluminescence properties by a hydrothermal method

Aggregated tin oxide (SnO2/SnO) nanostructures were produced in the presence of double tin salts (SnCl4·5H2O, SnCl2·2H2O), metal hydroxyl precursors (caustic soda and ammonia), poly(oxy)ethylene glycol-400 and water as a solvent, by a hydrothermal method. The crystal structure, functional groups, morphology, and photoluminescence properties of the SnO2/SnO nanostructures are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Energy dispersive X-ray (EDX), scanning electron microscopy (SEM) and Photoluminescence (PL) analysis. The XRD and SEM studies indicated the formation of a mixed phase of SnO2/SnO with a nanocrystalline nature. The FTIR and EDX analyses also confirmed the formation of the Sn–O bond. The PL emission spectrum of the SnO2/SnO nanostructures was observed in the visible region (blue, green, yellow and red emission peaks), due to the oxygen vacancies or other defects, and it could be used for luminescent device applications.

Swift heavy ion induced structural, optical and luminescence modification in NaSrBO3:Dy3+ phosphor

The effect of 120 MeVAg9+ ion irradiation on the structural, optical and luminescence properties of NaSr1-xBO3:xDy3+ (x = 0.5–2.5 mol%) phosphor synthesized by the conventional solid state reaction route is reported. The samples were irradiated with Ag9+ swift heavy ions (SHIs) using fluences of 1 × 1012, 5 × 1012 and 1 × 1013 ions cm−2. The unirradiated as well as irradiated samples were characterized by powder X-ray diffraction (PXRD), diffuse reflectance (DR) and photoluminescence techniques. PXRD confirms no change in the phase after irradiation except that loss of crystallinity had been observed which may be due to the fragmentation caused by the SHI. A blue shift in the absorption band of the DR was observed, resulting in an increase in the band gap from 5.61 eV to 5.77 eV, after ion irradiation. An increase in photoluminescence intensity (excited at 385 nm) was observed with increased ion fluences. The ratio of the blue to yellow emission peaks (I483/I577) was calculated and found to be varying with ion fluences suggesting that the white light can be achieved by tailoring this yellow to blue ratio. The Commission Internationale de l’Eclairage coordinates were calculated and found to move toward the white region after irradiation.

Electroluminescence of ZnO nanorods/ZnMgO films/p-SiC structure heterojunction LED

Through a facile low-temperature hydrothermal process, ZnO nanorod arrays were grown on ZnMgO films/p-SiC to form a heterojunction LED. ZnMgO films were grown on p-SiC by a simple sol–gel method. In this heterojunction structure, ZnMgO films works as the seeds film for the growth of ZnO nanorods. In particular, ZnMgO films can work as barrier layer between n-ZnO nanorods and p-SiC, which controls the movement of holes and electrons. Thus, with this introduced ZnMgO films, the electroluminescence (EL) from ZnO can be observed in ZnO/SiC heterojunction. Under a forward bias larger than 18V, the emission band in electroluminescence (EL) spectrum is considered as a combination of a peak centered at 388nm and a yellow band emission peak around 450nm. As the injection current increased, the intensity of ultraviolet emission was also increased. At last, the function of ZnMgO films in the heterojunction structure was discussed.

The excellent spontaneous ultraviolet emission of GaN nanostructures grown on silicon substrates by thermal vapor deposition

In this study, GaN nanostructures were grown on p-Si (111) substrate by thermal chemical vapor deposition (TCVD). Ga vapor directly reacted with NH3 solution in N2 carrier gas flow of 2L/min at different temperatures (950–1050°C). The influence of NH3 solution and growth temperature on the morphology, structure, optical and photoresponse properties of GaN nanostructures was investigated. Scanning electron microscopy images showed that the densities of the NWs varied with increasing temperature. The use of NH3 solution and increased growth temperature improved the crystalline quality of GaN nanostructures. The photoluminescence (PL) spectra of nanostructures displayed a near band-edge (NBE) emission at around 363–367nm. Higher growth temperature (1050°C) resulted in a strong NBE emission with no yellow emission peak. With +5V applied bias, the NWs metal–semiconductor–metal UV photodetector exhibited a high photocurrent of 1.6×10−3A. The photocurrent to dark current contrast ratio was 120.

Investigation of the effect of annealing on the photoluminescence properties of ZnO nanoparticles, synthesized at low temperature

ZnO nanoparticles were synthesized by a simple chemical precipitation method at 0°C and annealed in air at temperatures of 200, 400 and 600°C. Effect of annealing temperature on the optical properties were characterized by the UV–Vis and photoluminescence (PL) spectroscopy. The PL spectra of as prepared ZnO nanoparticles exhibits a narrow UV and a broad yellow emission peaks which are related to defect levels in the band gap. With the annealing temperature increasing, the intensity of yellow emission is strongly decreased, whereas the green emission is revealed. In addition, it was found that, there is a slight red shift in the UV absorption peak and a blue shift in the visible emission peak when the annealing temperature increases.