Blue Emission Peak Research Articles

Synthesis and luminescence properties of RE3+ (re = eu3+, Dy3+) activated CaSr2(PO4)2 phosphors for lighting and dosimetric applications

A series of RE3+ (RE = Eu3+, Dy3+) activated CaSr2(PO4)2 phosphors were successfully synthesized by the Solid-State Diffusion method at high temperature. X-ray diffraction (XRD) pattern and Fourier transform infrared (FT-IR) spectra explained the structural properties and crystalline nature of the prepared sample. The Scanning Electron Microscopy (SEM) study represents particle size and morphological behavior of the prepared sample. The luminescence properties of the prepared phosphor were investigated by Photoluminescence (PL) and Thermoluminescence (TL) techniques. The PL properties of Eu3+ activated CaSr2(PO4)2 phosphors monitored under near-ultraviolet excitation at 395 nm, exhibited two strong, orange and red emission peaks at 593 nm and 615 nm respectively corresponding to the characteristic 5D0→7F1 and 5D0→7F2 transitions of Eu3+ ions. Further, Dy3+ activated CaSr2(PO4)2 phosphors monitored under 350 nm excitation wavelength, exhibited two strong, blue, and yellow emission peaks at 481 nm and 572 nm respectively, corresponding to the characteristic 4F9/2→6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ion. The CIE chromaticity diagram shows high color purity and excellent chromaticity coordinates and it also shows the presence of emission bands in the visible spectrum. The TL properties of (RE = Eu3+, Dy3+) activated CaSr2(PO4)2 phosphors were investigated after irradiating the samples with 75 MeV Oxygen ion beam and Gamma rays. CaSr2(PO4)2:Eu samples show TL response linearity in the fluence range 5 × 1010 ions/cm2 to 1 × 1011 ions/cm2 whereas CaSr2(PO4)2:Dy samples show linearity in the range 5 × 1010 ions/cm2 to 5 × 1011 ions/cm2 when irradiated with 75 MeV O6+ ion beam. Further γ-ray irradiated CaSr2(PO4)2 samples show TL response linearity for dose range 1.75 kGy to 21.06 kGy when activated by Eu and 0.116 kGy to 2.32 kGy when activated by Dy. So, CaSr2(PO4)2 activated by RE3+ (RE = Eu3+, Dy3+) phosphor is a promising candidate for lighting and dosimetric applications.

Rise in UV and blue emission and reduction of surface roughness due to the presence of Ag and Al in monocrystalline ZnO films grown by sol-gel spin coating

ABSTRACT Highly transparent thin films of aluminium doped ZnO along with specific silver co-doping are deposited by sol-gel spin coating, which show preferred single orientation along (100) plane. Presence of Al dopant reduces, whereas co-doping with Ag improves crystallinity. Films show sharp absorption in near UV region and band gap observes minor shifts. UV and blue emission peaks are seen in the photoluminescence spectra. UV and blue emission peaks, respectively, demonstrate a fairly large i.e. 43% and 77% rise in the normalised intensity. Presence of Ag causes rise in UV peak because of enhanced excitonic recombination probability. Rise of blue emission intensity is ascribed to creation of Ag-Al interstitials. Surface roughness increases to 210.0 nm with Al increment into ZnO and drops drastically to 81.1 nm by Ag co-doping. Boundaries of nanostructures club together with rise in Al amount and thereafter Ag co-doping is seen to reduce the particle size.

Structural and luminescence properties of thermally stable cool-white light emitting NaCaPO4:Dy3+ phosphor

The photoluminescence (PL) properties of NaCaPO4:Dy3+ phosphor synthesized by sol-gel method forms the main focus of this report. The structural, morphological and luminescence properties of the NaCaPO4:Dy3+ phosphors were examined using X-ray diffraction, scanning electron microscopy and PL. The structure of the phosphor with the optimum Dy3+-concentration was refined using the Rietveld method. The PL spectra under 350 nm excitation revealed three peaks in the blue, yellow and red region. Stark splitting was observed for the blue emission peak. The thermal quenching behavior of the PL emission of the phosphor was analyzed to determine its thermal stability.

Carbon Quantum Dots as Fluorescence Turn-Off-On Probe for Detecting Fe3+ and Ascorbic Acid.

This work describes a "turn-off-on" fluorescence probe based on carbon quantum dots for sensing Fe3+ and ascorbic acid. The carbon quantum dots are prepared by hydrothermal method using a biocarbon source of black sesame. When excited at 355 nm, the carbon quantum dots show a strong bright blue emission peak centered at 438 nm. Obviously, the decrease of the fluorescence intensity of carbon quantum dots can be seen upon addition of Fe3+. Interestingly, the fluorescence quenching can be regained after the addition of ascorbic acid. The mechanism is that the added Fe3+ was destroyed by reductive ascorbic acid because of the redox reaction between ascorbic acid and Fe3+, making the fluorescence of the system recovered. The obtained curves are linear for Fe3+ and ascorbic acid over the range 50-1500 μM and 32.2-987.6 μM, respectively. The detection limits for Fe3+ and ascorbic acid are 2.78 μM and 0.0344 μM, respectively. Thus the carbon quantum dots can be used as a dual-function fluorescent sensor to achieve sensitive detection of Fe3+ and ascorbic acid.

Synthesis and luminescence properties of La(P1-yVy)O4: X at.% Tm3+as a blue emitting with high color purity phosphors

A blue light emitting phosphors of La(P1-yVy)O4:x at.%Tm3+ (y = 1.0, 0.9, 0.7, 0.5, 0.3, 0.1, 0.0) and different dopant concentration of Tm3+ (x = 1, 2, 3, 4, 5) have been synthesized via co-precipitation method. Detailed characterizations of the synthesized phosphors were performed by the powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy and photoluminescence (PL) emission and excitation spectroscopy. Typically Tm3+ ions have a blue emission peak around 455 nm, which is caused by the 1D4→3H6 transition energy level. By combining VO43- and PO43- groups, the color purity and photoluminescence (PL) intensity of the phosphors are improved, and the La(P0.1 V0.9)O4 composition was identified to show the optimal VO43- to PO43- ratio. Then, using the different concentration of Tm3+ as the active ions of the La(P0.1 V0.9)O4 matrix, and 2 at.% is found to be the quenching concentration, with the quenching mechanism is exhibited as dipole-dipole interaction.

Effect of cobalt doping on optical, magnetic and photocatalytic properties of ZnO nanoparticles

Cobalt doped ZnO nanoparticles (Zn1-xCoxO(0.00≤x≤0.1)) was synthesized by a two-step coprecipitation method using oxalic acid and ammonium hydroxide. The effect of Co doping on the crystallite structure, optical, magnetic and photocatalytic properties of ZnO was investigated. The X-ray powder diffraction (XRD) patterns confirmed that all Zn1-xCoxO samples exhibited hexagonal wurtzite structure. Further, the lattice parameters revealed an increasing trend in doped samples which indicated the incorporation of Co ions into the ZnO lattice. The X-ray photoelectron spectroscopic (XPS) survey suggested that Co ion incorporated into the ZnO lattice with a Co2+ oxidization state. The scanning electron micrograph (SEM) showed that the average size decreased with increasing doping concentration. Photoluminescence (PL) showed blue emission peak at 475 nm, green emission peak at 545 nm and yellow emission peak at 580 nm, respectively. UV–vis spectral illustrated the substitution of Co2+ in ZnO leaded to band gap narrowing. Vibrating sample magnetometer (VSM) demonstrated doped samples exhibited ferromagnetism behavior at room temperature. The Zn0.96Co0.04O sample showed enhancement in the photocatalytic degradation efficiency of methylene blue as compared to the pure ZnO. However, increasing doping concentrations of Co leaded to a decrease of photocatalytic efficiency.

The effect of annealing time on zinc selenide thin films deposited by photo-assisted chemical bath deposition

Zinc selenide (ZnSe) thin films were deposited on non-conducting glass substrates at 80 °C for 2.0 h in an alkaline medium using photo-assisted chemical bath deposition (PCBD). The films were annealed in air at 300 °C for different time intervals ranging from 0 to 4.0 h. The annealing time had a significant effect on the structure, morphology and optical properties of the deposited films. The glancing incidence X-ray diffraction (GIXRD) analysis confirmed polycrystalline films with a hexagonal wurtzite structure. The estimated crystallite size decreased with increasing annealing time. The as-deposited sample showed secondary peaks in the GIXRD and Raman spectroscopy due to unreacted selenium, which disappeared after annealing. Changes in surface morphology with increasing annealing time were observed using scanning electron microscopy. The energy dispersive X-ray spectrometer results showed an increase in zinc with a decrease in selenium for longer annealing times. The atomic force microscopy showed that the estimated films surface roughness decreased during annealing. Blue shifts in the absorption spectra and an increase in the energy bandgaps were observed with an increase in annealing time, together with an increase in optical transmittance. Photoluminescence spectroscopy revealed blue, green and red emission peaks, which were all attributed to the intrinsic defects within the ZnSe. The estimated decay lifetime showed that the average decay lifetime of the films increased with annealing time. Annealing for 3.0 h was found to be the optimum based on the response of the investigated properties.

Performance Evaluation of Single-Junction Indoor Photovoltaic Devices for Different Absorber Bandgaps Under Spectrally Varying White Light-Emitting Diodes

In this article, we present a detailed theoretical study to predict performance characteristics of single-junction indoor photovoltaic (PV) devices operated under white light emitting diodes (LEDs) having different spectral characteristics. Efficiency limits of both ideal and practical PV converters have been evaluated considering illumination by commercially available white LEDs. The obtained results have been generalized for white LED sources having a wide range of correlated color temperatures (CCTs) and fraction of blue in their corresponding spectrum. Depending on bandgap of the absorber material, both positive and negative correlations are observed between photon conversion efficiency of PV devices and CCT values of the white LED sources. For material bandgaps of ∼1.5 eV or lower, higher photon conversion efficiencies are obtained for warm glow white LEDs. On the contrary, white LEDs characterized to emit cool light are found to be more conducive for PV devices having absorber layer bandgaps of ∼2 eV or higher. The observed characteristics have been explained in terms of linewidth of the main emission peak and relative intensity of blue emission peak of the irradiating white LED spectrum. Based on the analysis of photon yield, three distinct bandgap ranges of the PV absorber material have also been identified, each of which represents different dependence of PV device performances on the white LED spectral characteristics. These results in effect provide the necessary guidelines for designing homojunction, heterojunction, or tandem PV devices suitable for operation under different practical white LED sources.

A novel near white light emitting phosphor KSrYSi2O7:Dy3+: Synthesis, characterization and luminescence properties

Novel KSrYSi2O7 phosphors doped with Dy3+were synthesized by combustion method. Varying the Dy3+ concentration confirmed a new lattice structure that has not been synthesized and reported before. The luminescence characteristics, thermal steadiness and quantum competence of the synthesized phosphor were studied in detail. The emission curves of the said material displayed an intense golden emission peak at 576 nm and a blue emission peak at 487 nm. The Commission Internationale del'Eclairage (CIE) parameters such as color coordinate and color associated temperature were computed by spectral energy circulation functions and the McCamy's empirical formula. The observed results revealed the appropriateness of the synthesized phosphor as a novel material for white light emitting applications.

Structural features, low-temperature luminescence properties of Li-doped SnO2 nanobelts and their transitional temperature

Li-doped SnO2 nanobelts have been fabricated by thermal evaporation based on vapor-solid (VS) growth mechanism. The three feature-peaks of Raman scattering spectra at 475 cm −1 (Eg), 634 cm −1 (A1g), and 776 cm −1 (B2g) at room temperature indicate that the samples still keep the rutile structure. One vibration mode at 591 cm−1 is observed from the Li-doped SnO2 nanobelts due to a slight distortion of SnO2. XPS spectra indicate that lithium is incorporated mainly in substitutional sites in the rutile structure of SnO2. The low-temperature (less than 90 K) photoluminescence properties show that there is an intensive broadband blue light emission centered at 480 nm (BL, 2.583 eV). When the temperature is larger than 90 K, the blue light emission peak is quenched and one yellow light emission centered at 580 nm (YL, 2.138 eV) is dominated. The analyses of Gaussian-fitted from 10 to 90 K reveal that the three peaks show different temperature dependences with increasing temperature. The characteristic temperature of quenching is the 90 K served as a transitional temperature. Activation energy of Ea about 40 meV is obtained from the integrated intensity of the YL band using the Arrhenius formula.

Effect of temperature and etching under light irradiation on the band edge emission of β-mercaptoethanol-capped CdS colloidal nanocrystals

In this work, cadmium sulfide nanocrystals capped with β-mercaptoethanol: CdS–βME (NCs) formed at wurtzite structure were prepared by colloidal chemical method for structural and optical properties' investigation. The temperature dependence of the photoluminescence (PL) intensity and its quantum yield (QY), the PL pic position and FWHM and the PL lifetime were systematically studied over a broad temperature range of 10–300 K. PL enhancement, photoetching and photostability of CdS–βME NCs were investigated under light irradiation. XRD and TEM patterns showed that CdS–βME NCs have an hexagonal phase with wurtzite structure. A very narrow excitonic blue emission peak with relatively high intensity was detected, which is similar to the better results obtained via organic synthesis. The FWHM ($$\sim$$ 20 nm) is controlled by an inhomogeneous broadening due to the particle size/morphology distributions of the NCs. Dynamic studies reveal shorter lifetimes indicating weak contribution of the surface-related emission with the removal of surface defects. The photoetching process of CdS–βME NCs resulted in a high QY of up to 3.8% with an obvious blueshift in band emission. On the basis of these studies, it is established that the surface of CdS–βME is rich with Cd2+ ions, leading to the formation of a CdO layer as shell, which provides a better passivation by removing surface hole traps and confines the charge carriers with illumination by Hg lamp radiation. In conclusion, owing to their excellent dispersibility in water and high luminescence, the CdS–βME NCs that have been developed here can be a promising candidate for biolabelling and imaging applications.

Synthesis and luminescence properties of Yb3+, Tm3+ and Ho3+ co-doped SrGd2(WO4)2(MoO4)2 nano-crystal

Novel up-conversion luminescent SrGd2(WO4)2(MoO4)2: Yb3+/Tm3+/Ho3+ nano-crystals were synthesized by hydrothermal method. The composition ratio of rare earth had been investigated. It indicated that when CYb3+ = 10 mol% and CYb3+/CTm3+/CHo3+ = 10:1.5:2, the emission intensities were the highest. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and up-conversion luminescence spectra were used to characterize SrGd2(WO4)2(MoO4)2: Yb3+/Tm3+/Ho3+ nano-crystals and they showed that the sample had high degree of crystallinity, the sample was tetragonal system, and the grain size of the sample was about 56 nm. Three emission peaks, including blue emission peak, green emission peak and red emission peak were observed at 477, 543 and 651 nm corresponding to 1G4 → 3H6 and 1G4 → 3F4 transitions of Tm3+, 5F4 → 5I8 and 5F5 → 5I8 transitions of Ho3+ respectively. All the emission peaks were observed by excitation of 980 nm semiconductor laser. The relationship between up-conversion intensity and excitation power revealed that blue emission at 477 nm was a three-photon absorption process, green emission at 543 nm and red emission at 651 nm was a two-photon absorption process. The quantum yields of the sample were near 3.2%.

Sb3+ Doping-Induced Triplet Self-Trapped Excitons Emission in Lead-Free Cs2SnCl6 Nanocrystals.

Doped halide perovskite nanocrystals (NCs) have opened new opportunities for the emerging optical and optoelectronic applications. Here, we describe a hot-injection synthesis of all-inorganic lead-free Cs2SnCl6 and Sb3+ doped Cs2SnCl6 NCs. Cs2SnCl6 NCs present a blue emission peak at 438 nm, whereas a new broad-band emission peak appears at 615 nm for the Sb3+ doped NCs. Comparative structural and spectral characterizations of Sb3+ doped Cs2SnCl6 NCs with micrometer-sized undoped and Sb3+ doped crystals show that the formation of broad-band orange emission is originted from triplet self-trapped excitons, attributed to the 3Pn-1S0 transitions (n = 0, 1, 2). Our results in Sb3+ doped Cs2SnCl6 materials provide insights into the machanisms of doping-induced emission centers, and it extends the existing knowledge of optical properties of doped halide NCs for further studies.

Effect of PO43−/VO43− proportion on structure and photoluminescence properties of Gd(PyV1−y)O4: X at.% Tm3+ phosphors

A series of Gd(PyV1−y)O4: x at.% Tm3+ (x = 1, 2, 3, 4 and 5; y = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1) phosphors were prepared by chemical co-precipitation method. The phosphors were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, photoluminescence excitation and emission spectroscopy. XRPD result suggests that when the concentration ratio of VO43− to PO43− exceeds 3∕7, the crystal structure of phosphors changes from monoclinic structure to tetragonal structure. Tm3+ ion has a typical blue emission peak around 477 nm, which is caused by the transition of 1D4→3H6 energy level. By mixing PO43− and VO43− groups, the photoluminescence intensity and color purity of the phosphors are improved, and the optimal PO43− to VO43− concentration ratio is identified to be 1∕9. Different concentrations of Tm3+ were then used as activating ions of Gd(P0.1V0.9)O4 matrix, and the quenching concentration is found to be 2 at.%, with the quenching mechanism being revealed to be dipole-dipole interaction.

Structural, optical, and luminescence properties of Cu2+-doped Ca-Li hydroxyapatite nanopowders prepared by mechanochemical synthesis

Novel luminescent phosphor materials have potential applications in lighting, display devices, and optical communication. In this study, novel Cu2+-doped calcium-lithium hydroxyapatite (CLHA) nanopowders were successfully fabricated by a simple mechanochemical technique. The synthesized samples were characterized by several microscopic and spectroscopic techniques. The hexagonal phase of the prepared sample was confirmed by x-ray diffraction results, and the average crystallite sizes were evaluated. Fourier transform infrared spectra demonstrated the formation of numerous vibrational modes ascribed to phosphate molecules and other hydroxyl groups. The morphologies of the Cu2+-doped CLHA nanopowders were investigated by scanning electron microscopy and transmission electron microscopy analyses. Optical absorption and electron paramagnetic resonance data indicated that the distortion of Cu2+ in the host lattice corresponds to the tetragonal site symmetry. Photoluminescence (PL) spectra of the Cu2+-doped CLHA nanopowders revealed strong blue and weak green emission peaks. From the PL emission spectra, the chromaticity CIE parameters were evaluated, and the results indicated that the prepared phosphor materials may be useful for lighting and display devices.

Red-orange photoluminescence emission of sol-gel dip-coated prepared ZnO and ZnO:Al nano-crystalline films

Zinc oxide films doped with 0–5 % wt. Aluminum (AZO) were prepared by sol-gel method and coated on glass substrate via dip-coating process. The sol was obtained with 0.5 M ethanolic solution of zinc acetate deposited into glass substrate with 200 mm/min withdrawing speed for 3 times. The deposited films were transformed into nanocrystalline undoped or Aluminum-doped ZnO after heat treatment at 400 ̊C for 2 h. Processing conditions and the effects of Al doping on crystallinity, morphology, and optical properties of ZnO films were characterized by X-ray diffraction (XRD), FESEM analysis, UV-VIS and photoluminescence spectroscopy. XRD analysis confirmed that all nano structured thin films have a hexagonal wurtzite structure. Results showed that Al doping has considerable effect on particle size, absorbance, transmittance and photoluminescence emission of samples. Depending on the Al concentration film transparency significantly increased, the highest transparency greater than 80% for 3 wt % AZO prepared films has been acquired. Accordingly the calculated optical band gap energy was varying from 3.2 to 3.7 eV related to Al doping level. The photoluminescence studies of undoped ZnO and AZO films have revealed very interesting features. Correspondingly photoluminescence spectra indicated that elaborated undoped ZnO and AZO films could emit luminescence emission over the entire visible region included violet emission peak at 413 nm, blue emission peak at 487 nm, green emission peak at 531 nm and orange-red emission peak at 630 nm that later is not very common in ZnO which is mainly attributed to Oi-related transitions.

Catalyst-free growth of ZnO nanowires: structural, optical, vibrational and field emission properties

High density of ZnO nanowires is grown over zinc foil by a catalyst-free thermal evaporation process. Electron microscopy studies confirmed that the as-grown nanowires are hexagonal wurtzite structure. The nanowires diameter was ~ 50 nm with typical length of the order of μm. Photoluminescence (PL) spectrum of the wires consist of a strong blue emission peak at 2.54 eV accompanied by other peaks of relatively lower intensities. The Raman spectra of the ZnO nanowires exhibit compressive stress due to the local heating effects during the synthesis. The field emission measurement indicated that ZnO nanowires have a turn-on field of 13.5 V/μm at current density of 0.001 μA/cm2.

Homogeneous ZnO nanowire arrays p-n junction for blue light-emitting diode applications.

ZnO is a promising short-wavelength light-emitting materials for its wide bandgap (3.37 eV) and large exciton binding energy (∼60 meV), however, practical p-type doped ZnO is the main challenge in this field. Here, Blue light-emitting diodes (LEDs) based on the homogeneous junctions of Sb doped ZnO nanowire arrays grown on Ga doped ZnO single crystal substrate are fabricated. Element analysis, FET and Hall-effect measurements demonstrate that the Sb atom has been successfully doped into ZnO nanowires to from p-type conductivity. On the benefit of high quality of nano-size homojunction, the fabricated LED shows low turn-on voltage turn-on voltage as low as 3.4 V and strong blue emission peak located at 425 nm at room temperature, which originate from interfacial recombination of ZnO nanowire p-n homojunctions. The present blue LED based on ZnO material may have potential applications in short-wavelength optoelectronic devices.

Physical properties of rare earth metal (Gd3+) doped SnO2 thin films prepared by simplified spray pyrolysis technique using nebulizer

Pristine and rare earth (i.e) gadolinium doped SnO2 thin films have been coated on micro-glass substrates with different Gd doping concentration at constant temperature 450 °C by simplified spray pyrolysis technique using nebulizer unit. The variation of doping concentration from 0 to 6 wt.% in the steps of 2 wt.%. Structural, optical, electrical, morphological and photoluminescence properties had been examined as a function of gadolinium doping level. The X-ray diffraction study exposed that all the prepared pristine and Gd doped SnO2 thin films are (110) preferred orientation with tetragonal crystal structure. The observed transmittance of Gd:SnO2 thin film varies between 91–80% in the visible regions. The estimated optical band gap value was initially decreased from 3.79 to 3.74 eV and then it was slightly increased as 3.77 eV with respect to the increase of Gd doping concentrations. Homogeneous surface morphology with polyhedrons like grains without cracks for all the prepared samples was illustrated by SEM studies. EDS spectra confirms that the existence of Sn, O and Gd elements in the 4% Gd doped SnO2 thin film surface. PL results indicates that three emission bands such as ultra violet, blue and green emission peaks at the wavelength of 360, 493 and 519 nm respectively, for all the prepared Gd:SnO2 films. Minimum resistivity (ρ) 7.14 × 10−4 Ω-cm with activation energy (Ea) 0.05 eV, maximum carrier concentration (n) 2.36 × 1020 cm−3 and figure of merit (ϕ) 52.96 × 10−3 (Ω/sq)−1 were obtained for 4% Gd doped SnO2 thin film using Hall effect measurements.

Effect of doping charge compensator Li+ on structure and luminescent properties of ZnWO4: Eu3+, Dy3+ phosphor

The white-light emitting phosphors ZnWO4:Eu3+,Dy3+ with Li+ as charge compensator were prepared by a hydrothermal method followed with calcination process. And the effects of Li+ doping amount on the structure and luminescent properties of samples were investigated. The results indicate that the introduction of Li+ has little effect on the crystal structure of samples. The particles of the phosphor are approximately spherical in shape, and the size is about 70–100 nm. The main excitation peak of samples is at 297 nm, ascribed to the W6+-O2− charge transfer state (CTS) transition. The emission spectra are composed of blue-green emission band of WO42−, yellow and blue emission peaks of Dy3+, and red emission peaks of Eu3+. With the increase of Li+ doping amount, the emission intensity of Dy3+ firstly increases and then decreases, but the emission intensity of WO42− decreases gradually, and that of Eu3+ remains almost unchanged. When the doping amount of Li+ is 2.5%, the yellow emission intensity of Dy3+ (576 nm) reaches the highest, which is 1.26 times of the uncompensated sample. The emitting color of phosphors can be tuned from the blue-white light through white light to the yellowish-white zone by the increase of Li+ doping amount.