Strong Visible Emission Research Articles

Short-Wave Infrared Upconverting Nanoparticles.

Optical technologies enable real-time, noninvasive analysis of complex systems but are limited to discrete regions of the optical spectrum. While wavelengths in the short-wave infrared (SWIR) window (typically, 1700-3000 nm) should enable deep subsurface penetration and reduced photodamage, there are few luminescent probes that can be excited in this region. Here, we report the discovery of lanthanide-based upconverting nanoparticles (UCNPs) that efficiently convert 1740 or 1950 nm excitation to wavelengths compatible with conventional silicon detectors. Screening of Ln3+ ion combinations by differential rate equation modeling identifies Ho3+/Tm3+ or Tm3+ dopants with strong visible or NIR-I emission following SWIR excitation. Experimental upconverted photoluminescence excitation (U-PLE) spectra find that 10% Tm3+-doped NaYF4 core/shell UCNPs have the strongest 800 nm emission from SWIR wavelengths, while UCNPs with an added 2% or 10% Ho3+ show the strongest red emission when excited at 1740 or 1950 nm. Mechanistic modeling shows that addition of a low percentage of Ho3+ to Tm3+-doped UCNPs shifts their emission from 800 to 652 nm by acting as a hub of efficient SWIR energy acceptance and redistribution up to visible emission manifolds. Parallel experimental and computational analysis shows rate equation models are able to predict compositions for specific wavelengths of both excitation and emission. These SWIR-responsive probes open a new IR bioimaging window, and are responsive at wavelengths important for vision technologies.

Synthesis, optical absorption, luminescence, chromaticity, and catalytic properties of undoped CuO and Gd-doped CuO nanostructures for LED devices and waste water treatment applications

The first objective of this present investigation is the co-precipitation synthesized of undoped and various concentrations of Gd-doping in the CuO material as a photocatalyst and methylene blue dye under passing solar light radiation, followed by obtaining their photocatalytic degradation efficiency of 88–96%. Using photoluminescence (PL) data of synthesized undoped and 1%, 3%, and 5 wt% Gd-doped CuO to make a chromaticity diagram for identifying the colour coordinates to scrutinize the applications of light-emitting devices. To trace the diffraction peaks, related crystal system, and vibrational bond of undoped and Gd-doped CuO materials by XRD and FT-IR studies. The morphological structure has been varied in each Gd-dopant concentration when compared to undoped CuO nanostructures through SEM studies. The aforementioned material has a narrow band gap and strong visible emission, as identified by UV–visible and PL spectra.

Highly sensitive optical thermometer based on Li+-doped erbium ytterbium silicate films

This work provides a new material, Li+-doped erbium ytterbium silicate, with reliable and high temperature sensing sensitivity for optical thermometers. The Li+-doped erbium ytterbium silicate films were prepared by RF magnetron sputtering. The film shows strong green visible emission, which is related to the radiation transitions from thermally coupled energy levels 2H11/2, 4S3/2 to 4I15/2. Lithium doping reduces the field symmetry around erbium and improves the radiation transition efficiency, and Yb doping improves the pump light absorption. Lithium or ytterbium is advantageous to enhance up-conversion luminescence and temperature sensing sensitivity of erbium ions. Therefore, the temperature dependence of green up-conversion luminescence in the range of 80–460 K of the Li+-doped erbium ytterbium silicate films have been found to be a promising optical thermometer material with a high relative sensitivity of 16.9 % K−1, which is higher than the optimum value of other Er3+ materials. In addition, we have provided a preliminary temperature measurement scheme based on the Li+-doped erbium ytterbium silicate film.

Structural and luminescent performance and optical thermometry of Pr3+ doped SrWO4 down-conversion phosphors

A series of Pr3+ doped SrWO4 phosphors were synthesized using solid-state reaction routes. The phase composition, photoluminescence and temperature sensitivities of as-prepared materials were investigated. Rietveld refinement of measured XRD data was applied to analyze the lattice parameters. The optical transition was elaborated using UV–visible diffuse reflectance spectra and photoluminescence spectra. The photoluminescence measurements confirmed the strong visible light emission from the developed phosphors under both UV excitation at 250 nm and blue excitation at 450 nm. Notably, the maximum emission intensity was observed at a Pr3+ doping concentration of 2 mol%. Furthermore, the fluorescence intensity ratio (FIR) technique was employed, focusing on the emissions originating from the 3P0 and 1D2 state of Pr3+ within the temperature range of 298–598 K. Two FIR groups were adopted in this case, which can verify each other to achieve self-calibration. Typically, SrWO4:0.02Pr3+ exhibited remarkable performance as a temperature sensor, displaying an absolute sensitivity (Sa) of 3.11%K−1 and a relative sensitivity (Sr) of 0.81%K−1. As a result, the significant temperature-dependent PL and remarkable down-conversion luminescence make the SrWO4:Pr3+ material a promising candidate for optical thermometers and UV to visible converters of solar cell applications.

Structural and photoluminescence properties of Sm3+ ions doped strontium yttrium tungstate phosphors for reddish-orange photonic device applications

In the present research work, Sm3+ ions doped Strontium Yttrium Tungstate (Sr9Y2W4O24) phosphors entitled to emit reddish-orange light have been synthesized using the conventional solid-state reaction method and analyzed their structure and phase using X-ray diffraction (XRD) patterns. The diffraction peaks of the Sr9Y2W4O24 phosphor matches very well with the standard JCPDS pattern with card no. 49-0568. The morphological behaviour of the as-synthesized phosphor has been studied using scanning electron microscopy (SEM). Different vibrational bands present in the titled phosphor have been examined using Fourier Transform Infrared (FT-IR) spectroscopy. The optical band gap values of the as-synthesized phosphors have been measured using diffuse reflectance spectra (DRS). The photoluminescence (PL) spectral features recorded for Sm3+ ions activated Sr9Y2W4O24 phosphor under 405 nm excitation reveal strong visible reddish-orange emission at 604 nm pertaining to the 4G5/2 → 6H7/2 transition of Sm3+ ions. Also the PL spectra show concentration quenching at 2 mol% of Sm3+ ions doped in to them. From the recorded PL spectra, the CIE chromaticity coordinates estimated for Sr9Y2W4O24:2.0mol% of Sm3+ phosphor are falling in deep visible reddish orange region. The PL decay spectral profiles recorded at 604 nm emission under 405 nm excitation are showing double exponential behavior and the experimental lifetimes are found to be decreasing with increase in Sm3+ ions concentration in the assynthesized phosphors. The temperature-dependent PL (TD-PL) measurements demonstrate relatively better thermal stability for the as-synthesized phosphor. All the investigations carried out finally allows us to contemplate the suitability of Sm3+ ions doped Sr9Y2W4O24 phosphor for reddish-orange photonic device applications.

Branched MgO Nanowires Synthesized by Thermal Evaporation Method in Air at Atmospheric Pressure

MgO nanowires with a branched structure were fabricated using a thermal evaporation method in air at atmospheric pressure. The branched MgO nanowire was made up of two parts: a primary central nanowire trunk and lots of secondary nanowire branches. The branched MgO nanowires had a 4-fold symmetrical structure. The secondary nanowire branches grew perpendicular on the four side facets of the central nanowire trunks with square cross-sections. The nanowire branches also grew in a single row and were vertically well aligned in the same direction with each other. The scanning electron microscopy images of the branched nanowires grown at 1000<sup>o</sup>C showed that the diameter of branches gradually decreased along the growth direction and no catalyst particle was found at the tips of the branches, indicating that the branches were grown by a vapor-solid process. For the branched nanowires grown at 1150<sup>o</sup>C, spherical particles which were shown to be catalysts were observed at the tips of the branches. The chemical analysis by energy dispersive spectroscopy showed that the spherical particles were composed of Mg and O elements. These results suggest that the branches’ growth resulted from a self-catalyzed vapor-liquid-solid process. The structural characterization by X-ray diffraction confirmed that the branched MgO nanowires had a cubic lattice structure. The room temperature cathodoluminescence spectra of the branched MgO nanowires exhibited a very strong visible emission which was associated with oxygen vacancies.

Effect of Carrier Gas Flow Rates on the Structural and Optical Properties of ZnO Films Deposited Using an Aerosol Deposition Technique

Aerosol deposition (AD) is a simple, dry raw-powder deposition process in which the targeted film is formed by direct bombardment of accelerated starting powder onto the substrate surface at room temperature. Despite the increased interest in AD film formation, no work has been completed to systematically investigate the formation of dense zinc oxide (ZnO) films using the AD method and their optical properties. Therefore, this study was carried out to investigate the effect of AD gas flow rate on the formation of AD films and the optical properties of aerosol-deposited ZnO films. ZnO films with nanosized (<40 nm) crystallites were successfully deposited on FTO substrates at room temperature. A dense and uniform layer of aerosol-deposited ZnO films with a roughened surface was obtained without subsequent heat treatment. With the increase in the AD gas flow rate, the crystal size and the AD film’s thickness were reduced. The Raman spectroscopy verified that the thin film was of a ZnO wurtzite structure. The room temperature photoluminescence of the ZnO thin film produced strong visible emissions. The findings of this work demonstrated that AD can be an alternative technique for the rapid deposition of dense and thick ZnO films for optoelectronic applications.

A single-phase white-emitting La(BO3,PO4):Dy3+ phosphor with high thermostability

Developing single-phase white-emitting phosphor has increasingly become an effective strategy to solve the emerging challenges of multiple phosphors-converted white light-emitting diodes such as unavoidable reabsorption, high production cost, and low thermostability. In this work, a single-phase white-emitting La(BO3,PO4):Dy3+ phosphor was synthesized. The photoluminescence performance characterizes the two strong visible emissions of Dy3+: blue (470–500 nm, 4F9/2 → 6H15/2) and yellow lights (570–600 nm, 4F9/2 → 6H13/2). The content quenching of Dy3+ presents at x = 0.03 mol, which is controlled by the dipole–dipole interaction. The optimized product La0.97Dy0.03(BO3,PO4) has a high thermostability. It has also the comparable color coordinates with the ideal white light due to the proper yellow-blue intensity ratio. The above studies confirm that the Dy3+-activated La(BO3,PO4) phosphor could be a prospective white-emitting candidate in lighting application.

Green synthesis of multifunctional ZnO/chitosan nanocomposite film using wild Mentha pulegium extract for packaging applications

Following the global corona virus pandemic and environmental contamination caused by chemical plastic packaging, awareness of the need for environmentally friendly biofilms and antibacterial coatings is increasing. In this study, a biodegradable hybrid film, comprising of green-synthesized zinc oxide nanoparticles (ZnO NPs) with a chitosan (CS) matrix, was fabricated using a simple casting procedure. The ZnO NPs were synthesized using wild Mentha pulegium extract, and the synthesized NPs and films were characterized using different approaches. The structural, morphological, mechanical, antibacterial, and optical properties, as well as the hydrophilicity, of the prepared samples were investigated using various techniques. Gas chromatography-mass spectrometry measurements revealed the presence of phenolic compounds in the M. pulegium extract. In addition, a strong coordination connection between Zn2+ and the chitosan matrix was confirmed, which resulted in a good dispersion of ZnO in the chitosan film. The surface of the composite films was transparent, smooth, and uniform, and the flexible bio-based hybrid films exhibited significant antibacterial and antioxidant characteristics, strong visible emission in the 480 nm region, and UV-blocking properties. The ZnO/CS films displayed a potential to extend the shelf life of fruits by up to eight days when stored at 23°C, and also acted as an acceptable barrier against oxygen and water. The biodegradable ZnO/CS film is expected to keep fruit fresher than general chemical plastic films and be used for the packaging of active ingredients.

Synthesis and Photoluminescence characterization of ZnAl12O19 : Sm3+ Phosphor for W-LED

The combustion process was used to create an effective ZnAl12O19:Sm3+ phosphor with reddish emission. Using scanning electron microscopy, the structural and morphological characteristics of the phosphor have been studied. Samarium ions are found in trivalent oxidation states, as demonstrated by the photoluminescence spectrum. The as-prepared phosphor exhibits strong visible red emission at 615 nm under 405 nm excitation. It has been discovered that a concentration of 1.5 mol% Sm3+ ions produce the strongest visible red emission. The synthesized phosphors 615 nm (x = 0.680, y = 0.319) and 661 nm (x = 0.730, y = 0.269) CIE colour chromaticity coordinates are located in the red area of the chromaticity diagram. All of these findings support the suitability of Sm3+-doped ZnAl12O19 phosphor for lighting and display applications.

LUMINESCENCE PROPERTIES OF NaMg4(PO4)3: Mn2+ CERAMIC POWDERS

Various concentration of manganese metal ions (x = 0.01, 0.02, 0.03, 0.04, 0.05 mol%) doped Sodium Magnesium Phosphate (SMP) NaMg4(PO4)3 compounds were made through combustion-reaction method. The powder X-ray diffraction (XRD) pattern confirms that Mn2+ ions were incorporated into the NaMg4(PO4)3 host lattice forming a complete solid solution. Elemental analysis and surface morphology were examined from the EDX spectrum and corresponding element mapping by scanning electron microscopy. The Photoluminescence spectra of Mn-doped SMP samples exhibited a strong visible emission peak at the wavelength of 617 nm, which indicated that spinforbidden transition takes place from 4T1g (G) to 6A1g (S) with inversion symmetry. The photoluminescence profiles exhibited the quenching in emission intensity above 0.03 mol% of Mn(NO3)2 due to the availability of more octahedral Mn2+ ions. These outputs show that Mn2+ activated NaMg4(PO4)3 material can fulfill application in redemitting phosphor-based LEDs devices.

Low-Temperature Chemical Vapor Deposition Growth of MoS2 Nanodots and Their Raman and Photoluminescence Profiles

We report on the growth of an ordered array of MoS2 nanodots (lateral sizes in the range of ∼100–250 nm) by a thermal chemical vapor deposition (CVD) method directly onto SiO2 substrates at a relatively low substrate temperature (510–560°C). The temperature-dependent growth and evolution of MoS2 nanodots and the local environment of sulfur-induced structural defects and impurities were systematically investigated by field emission scanning electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. At the substrate temperature of 560°C, we observed mostly few-layer MoS2, and at 510°C, multilayer MoS2 growth, as confirmed from the Raman line shape analysis. With reduced substrate temperature, the density of MoS2 nanodots decreases, and layer thickness increases. Raman studies show characteristic Raman modes of the crystalline MoS2 layer, along with two new Raman modes centered at ∼346 and ∼361 cm−1, which are associated with MoO2 and MoO3 phases, respectively. Room temperature photoluminescence (PL) studies revealed strong visible PL from MoS2 layers, which is strongly blue-shifted from the bulk MoS2 flakes. The strong visible emission centered at ∼ 658 nm signifies a free excitonic transition in the direct gap of single-layer MoS2. Position-dependent PL profiles show excellent uniformity of the MoS2 layers for samples grown at 540 and 560°C. These results are significant for the low-temperature CVD growth of a few-layer MoS2 dots with direct bandgap photoluminescence on a flexible substrate.

Hot-carrier radiative recombination through phonon confinement in silicon nanocrystals embedded in colloidal xerogel matrix

Colloidal suspension of free standing silicon/silicon oxide core/shell nanoparticles has been synthesized using a mechanochemical top-down approach. Quasi-mono-dispersed core size distribution of synthesized nanoparticles has been confirmed using different structural, morphological, and optoelectronic characterizations. Raman, continuous wave photoluminescence and time-resolved photoluminescence studies have been performed on synthesized colloidal nanoparticles in ethanol medium. Asymmetric broadening of the Raman peak (red shifted with respect to that of bulk silicon) has been observed. Intensities and positions of photoluminescence emission peaks are prominently dependent on excitation photon energy. Moreover, the photoluminescence decay time varies from sub-nanoseconds to tens of nanoseconds. The decay time also exhibits a strong dependence on the excitation wavelength, while the emission wavelength is kept unaltered. The abovementioned observations indicate the slow relaxation of photo-excited carriers in silicon quantum dots. This particular phenomenon takes place due to phonon mode discretization, which is further responsible for the radiative recombination of hot-carriers and consequent strong visible emission. The enhancement of hot-carrier lifetime in colloidal silicon quantum dots is the key requirement for the active material of the hot-carrier solar cell. Runny texture of the synthesized material inhibits practical device implementation; therefore, the synthesized nanoparticles have been embedded in the silica xerogel matrix. The impression of phonon mode confinement, in silicon quantum dots embedded in a hard matrix, has been observed, resulting in increased hot-carrier lifetime. The enhanced hot-carrier lifetime can lead to the realization of a silicon-based active material for the hot-carrier solar cell.

Effect of polyethylene glycol capping on structural, optical and thermal properties of ZnS:Ni2+ nanoparticles

To study the effect of polyethylene glycol capping on structural, optical and thermal properties, ZnS:Ni2+ nanoparticles have been prepared by chemical precipitation method. It is demonstrated that by varying the concentration of PEG the particle size can be varied within ∼3.58 to 12 nm. To analyze the samples of nanostructures, the samples are subjected to X-ray diffraction, Field emission scanning electron microscopy and High resolution transmission electron microscopy characterization techniques. The spectral bands between 673 and 494 cm−1 are related to Zn-S stretching vibrations which was confirmed by Fourier transform infrared spectral studies. It is found that the uncapped sample emits strong UV light, whereas the capped samples exhibit strong and broad visible emission. An enhancement of fluorescence intensity has been obtained, in a capped sample with the minimum particle size and thus with more defect centers, in comparison to that of uncapped one.

Synthesis and optimization of photoluminescence properties in potential reddish orange emitting niobate phosphor for photonic device applications.

A series of samarium ions (Sm3+ ) activated barium sodium niobate (Ba2 NaNb5 O15 ) samples have been successfully synthesized via employing a solid-state reaction technique. Single phase, crystalline tetragonal Ba2 NaNb5 O15 were formed and the crystallite size of the prepared sample varied with doping of Sm3+ ions. The scanning electron microscopy (SEM) images of Ba2 NaNb5 O15 :Sm3+ illustrate that the particles possess a non-uniform spherical structure with some agglomeration. The prepared Ba2 NaNb5 O15 :Sm3+ phosphors were efficiently excited with near-ultraviolet (n-UV) (406 nm) and emit strong visible emission peaks in the range 550-725 nm. The phenomenon of concentration quenching was detected after x = 0.10 mol of Sm3+ ions concentration for Ba2 NaNb5 O15 , which arises due to non-radiative energy transfer through dipole-dipole interaction among activator ions. Colour coordinates (0.586, 0.412) for the optimized phosphor lies in the visible reddish orange region. A bi-exponential decay behaviour was observed for the photoluminescence decay curve of the optimized phosphor sample with an average decay time in milliseconds. The temperature dependent emission intensity confirms that the Ba2-x NaNb5 O15 :xSm3+ (x = 0.10 mol) phosphor exhibits adequate thermal stability having high value of activation energy (ΔE = 0.201 eV). The comprehensive study and analysis of the as-prepared samples suggest that the intense reddish orange emitting thermally stable Ba2 NaNb5 O15 :Sm3+ phosphor can act as a potential luminescent material in phosphor coated lighting, solar cells and other photonic devices.

Improved morphology and excitonic emission of 2D MoS2 by incorporating mechanical grinding in the liquid phase exfoliation synthesis process

Abstract MoS2 nanosheets are synthesized by incorporating a manual grinding of the bulk powder prior to the sonication in the standard liquid phase exfoliation process. The light emission properties of MoS2 is thereby found to be significantly improved. Transmission electron microscopy shows continuous ultrathin MoS2 nanosheets of larger dimensions in the grinding-assisted synthesis. Raman spectroscopy measurements show that MoS2 is exfoliated down to 3–4 layers by an inclusion of the grinding. UV–visible and photoluminescence spectroscopy were used to analyze the changes in the optical properties. Grinding helps to reduce the influence of the degradation of the NMP solvent on the emission characteristics of the exfoliated material. The strong visible photoluminescence emission due to sonochemical degradation of NMP is suppressed and the excitonic emission due to the A and B excitons relative to NMP emission is significantly enhanced. The results suggest an easy and reliable approach to enhance the optical emission of two-dimensional MoS2 appreciably.

In-air self-reduction synthesis and luminescence properties from Mg21 Ca4 Na4 (PO4 )18 :Eu2+ -Eu3+ excited using ultraviolet light.

A series of Mg21 Ca4 Na4 (PO4 )18 :Eu2+ -Eu3+ phosphors was successfully synthesized using a high-temperature solid-state method in an air atmosphere. The phase structures and luminescence properties of the samples were studied in detail. The phosphors exhibited strong visible light emission under different wavelengths of ultraviolet light excitation. By harmonizing the doping concentration of Eu3+ to adjust the relative luminescence intensity of Eu2+ and Eu3+ , a colourful emission of phosphors could be achieved. In addition, the colour coordinates of the International Commission on lighting indicated that Mg21 Ca4 Na4 (PO)18 :Eu2+ -Eu3+ could be considered as a potential blue, orange and red phosphor for white light-emitting diode applications.

4H-SiC p-n Junction-Based Near IR Photon Source

We propose a Near Infra Red photon emitting 4H-SiC compact vertical pn diode. The “as fabricated” diode exhibits a strong visible emission at 500 nm associated with the intrinsic and/or processing induced D1 centers in the semiconductor. Thanks to opportune He <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ion irradiation, we are able to obtain color centers in the junction region responsible for photon emission around 900 nm while simultaneously quenching unwanted visible emission. Electro-optical investigation was conducted by Electro-Luminescence measurements in the 300 nm -1100 nm range and by Emission Microscopy, both with pumping a current between of 0.1 and 2 mA. The proportionality of the emission intensity to the pumping current opens the interesting perspective of engineering the concentration of defects with the aim of obtaining single defects and thus single photon source devices. This is of considerable interest in low-power proximity sensors for consumer, industrial, automotive and telecommunications applications.

Liquid crystalline behavior and photoluminescence of lanthanide decanoate nanoparticles synthesized by microwave radiation.

Luminescent lanthanide decanoate nanoparticles (LnC10 NPs; Ln = Pr, Nd, Sm, Eu, Gd, Er) with spherical morphology (<100 nm) have been synthesized via a facile microwave (MWV) method using Ln(NO3)3·xH2O, ethanol/water, and decanoic acid. These hybrid nanomaterials adopt a lamellar structure consisting of inorganic Ln3+ layers separated by a decanoate anion bilayer and exhibit liquid crystalline (LC) phases during melting. The particle size, crystalline structure, and LC behavior were characterized using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and powder X-ray diffraction (ambient and heated). Thermal analysis indicated the formation of Smectic A LC phases by LnC10 nanoparticles, with the smaller lanthanides (Ln = Sm, Gd, Er) displaying additional solid intermediate and Smectic C phases. The formation of LC phases by the smaller Ln3+ suggests that these nanoscale materials have vastly different thermal properties than their bulk counterparts, which do not exhibit LC behavior. Photoluminescence spectroscopy revealed the LnC10 NPs to be highly optically active, producing strong visible emissions that corresponded to expected electronic transitions by the various Ln3+ ions. Under long-wave UV irradiation (λ = 365 nm), bright visible luminescence was observed for colloidal suspensions of Nd, Sm, Eu, Gd, and ErC10 NPs. To the best of the authors' knowledge, this is the first reported synthesis of nanoscale metal alkanoates, the first report of liquid crystalline behavior by any decanoate of lanthanides smaller than Nd, and the first observation of strong visible luminescence by non-vitrified lanthanide alkanoates.

Emission properties of textured gallium nitride with high density of stacking faults

In this study we related structural properties of GaN grown on ceramic substrate and studied with transmission electron microscopy with the results of photo-and cathodoluminescence investigations. We found that stacking faults in the basal plane were responsible for both strong room temperature visible emission and exciton-related ultraviolet luminescence at cryogenic temperature.