Composite Phosphor Research Articles

Synthesis and characterization of near UV excitable Y2O2S:Eu3+ entrapped ZnO for white light emitting diode applications

Near UV excitable, white light emitting Y2O2S:Eu3+ entrapped ZnO has been prepared by sol-gel combustion method from zinc acetate, urea and Y2O2S:Eu red phosphor. In order to study the generation of white light, red phosphor has been entrapped in ZnO in various weight ratios (90:10, 50:50, 70:30). At the excitation of near UV light at 375 ​nm, this phosphor entrapped ZnO composite shows an white light emission, and it also comprises bluish green and red light emission in the wide range of wavelength starting from 420 to 650 ​nm, originated from the ZnO and Y2O2S:Eu3+, respectively. A highest photo-luminescent intensity with white light could be obtained for Y2O2S:Eu3+ and ZnO in the weight ratio of 70:30.The obtained light shows a warm white light with a CRI of 75 and color co-ordinates of (x ​= ​0.44, y ​= ​0.35). This phosphor composite could be useful for white light emitting diode applications.

Gamma‐Ray Irradiation Assisted Polyacrylamide Gel Synthesis of Scheelite Type BaWO4 Phosphors and Its Colorimetric, Optical and Photoluminescence Properties

AbstractA gamma‐ray irradiation assisted polyacrylamide gel method is used to synthesize the scheelite‐type barium tungstate (BaWO4) phosphors with space group I41/a(88). Various instruments were employed to characterize and reveal the phase purity, microcosmic characteristics, chemical composition, surface micromorphology, colorimetric, optical and photoluminescence properties of BaWO4 phosphors. The phase structure and functional group analysis showed that the formation temperature of pure BaWO4 phosphor was 100 °C lower than calcium tungstate (CaWO4) and strontium tungstate (SrWO4). The characterization of particle growth showed that BaWO4 was easy to grow along (112) and (200) crystal planes. The optical band gap (Eg) value of BaWO4 first increases and then decreases with the increasing of sintering temperature. The sintering temperature causes the BaWO4 xerogel to produce a variety of colors from black to white. The photoluminescence spectra showed that two obvious emission peaks at 380 and 415 nm are observed when the excitation wavelength is 334 nm. The former is ascribed to the T1(2)→A1(1) transition and the latter could be attributed to the defect energy levels in the BaWO4 phosphors. The intensity of emission peak at 380 nm decreases with the increasing sintering temperature. The photoluminescence mechanism of scheelite‐type BaWO4 phosphor was explored on the basis of energy band theory and experimental results.

Combustion-relevant aerosol phosphor thermometry imaging using Ce,Pr:LuAG, Ce:GdPO4, and Ce:CSSO

Aerosol phosphor thermometry (APT) is a promising temperature-imaging diagnostic that is currently being developed for combustion applications. To date, gas-phase APT measurements have been limited to temperatures below 1000 K due to thermal quenching and poor sensitivity at high temperatures. In this work, three phosphor compositions are investigated for application at flame relevant temperatures: Ce,Pr:LuAG, Ce:GdPO4, and Ce:CSSO. The phosphors were characterized in a temperature-controlled furnace, and measurements of gas temperature were performed in a seeded air jet after mixing with the products of an atmospheric methane-air flame. Furnace and flame measurements demonstrate that two of the phosphors are capable of temperature imaging at over 1000 K, with an upper temperature limit of at least 1400 K. Temperature precision estimates indicate 20-K or better single-shot precision from 500 to 1300 K for a seeding density corresponding to an added heat capacity of less than 1% of that of air at 1200 K at a spatial resolution of 1.12 line pairs per millimeter. This work represents the highest reported temperature measurements made using any APT technique for gas temperature measurements, and represents the highest measured quenching temperature of any phosphor exhibiting fast allowed emission for APT. These results extend the capabilities of APT for single-shot gas-phase temperature imaging up to at least 1400 K. This new capability will allow APT to be applied in combustion environments to study problems such as low-temperature ignition in engines.

Synthesis and up-conversion properties of Er3+ doped ZnTiO3-Zn2TiO4 composite phosphor

The conventional solid state reaction method was used to prepare Er3+ activated ZnTiO3-Zn2TiO4 composite phosphor. The structure, particle morphology, absorption, and photoluminescent properties were analyzed using x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis-NIR absorption spectrometer, and photoluminescence (PL) spectroscopy, respectively. The XRD confirmed the crystallization of mixed hexagonal ZnTiO3 and cubic spinel Zn2TiO4 phases. The SEM data showed that the prepared phosphor was made up of faceted hexagons. Furthermore, the phosphor was excited in the near-infrared (NIR) region using a laser diode with a wavelength of 980 nm, and the corresponding up-conversion emission lines were observed in the visible range at 543, 553, and 650–670 nm, associated with the 2H11/2 → 4I15/2, 4S1/2 → 4I15/2, and 4F9/2 → 4I15/2 transitions of Er3+ ions, respectively. The interaction mechanisms involved in the up-conversion process of ZnTiO3-Zn2TiO4:Er3+ phosphor are discussed with the help of an energy-level schematic diagram, and the number of the photons involved in the up-conversion luminescence process was estimated.

Optimization and photoluminescence behaviour of terbium doped YBO3 phosphors

Terbium doped yttrium borate phosphors have been prepared through solid state mixing method at 1200 °C. The concentration of Tb3+ ions has been varied in order to optimize the effective generation of green emission in Tb3+-doped yttrium borate phosphors. X-ray diffraction analysis suggested that the phase pure YBO3 was observed in all samples, and FESEM analysis confirmed that the particles were polyhedral and dumb-bell in shape. A detail photoluminescence behaviour of Tb3+-doped phosphors have been carried out under different excitation wavelengths. The PL behaviour suggested that the characteristic peaks due to Tb3+-ions appeared along with decrease in the broad peak intensity of the host with increase in the excitation wavelength. The optimum concentration of Tb3+ ions was found 5 and/or 10 mol % based on the PL behaviour. CIE coordinates suggested that the 5 mol % Tb3+-doped YBO3 sample has better chromaticity than that of other Tb3+-doped YBO3 phosphor compositions.

Effect of Bambara Nut Flour Addition on Proximate, Mineral Composition and Sensory Quality of Millet Based Madidi: A Nigerian Solid Gel Food

Madidi was produced from different formulations of pearl millet ogi and bambara nut flours. Five madidi products were produced at the laboratory scale using 100:0 (control), 95:5, 90:10, 85:15 and 80:20 millet to bambara groundnut flours, respectively. Bambara ground nut were cleaned, sorted (to remove foreign materials), soaked in cold water for 2 hours, dried and toasted for 30 minutes by using oven. The five formulated products were subjected to proximate, minerals and sensory analysis. The results showed that the protein contents increased with increased addition of bambara groundnut flour. The protein contents ranged from 1.79 to 3.51% on dry weight basis. The fat contents ranged from 0.26 to 1.22%. Carbohydrate content decreased from 22.00 to 13.21% as the proportion of bambara flour increased. Magnesium and phosphorous increased significantly (p=0.05), however potassium and iron were not significant affected (p=0.05). The 100% millet (0.17 mg/100 g) was significantly high in magnesium (p=0.05) followed by 95% millet and 5% bambara nut (0.09 mg/100 g). The phosphorous composition increased with increase in bambara nut (0.17– 0.22 mg/100 g). The average scores of parameters for all the products are relatively high. Product 85:15 millet to bambara flour was most acceptable. It is concluded that an acceptable madidi can be produced from millet and bambara nut at 15% substitution level.

Effects of the origins and stabilization of biosolids and biowastes on their phosphorous composition and extractability

Phosphorous dissolution and ensuing chemical redistribution of P in organic amendments (OA) were studied by applying a modified Hedley selective fractionation to eight water-extracted and unextracted OAs. Nine 7-day, repeated extractions were applied using a 60:1 water:dry OA (v:w) ratio at pH 8. Eight OAs were tested including five biosolids, broiler litter, dairy manure compost and municipal solid waste compost. The average PWEP9 (percent water-extractable P following nine water-extraction cycles) for the OAs was 65 ± 9% and all of the fractions, with almost no exceptions, contributed to that figure. Organic P was depleted by mineralization (in non-stabilized sludges and broiler litter) or dissolution (stabilized composts) or both (in lime-treated biosolids) and that depletion was completed within 1–2 extraction cycles. Only the organic P of the MSWC remained undepleted. Strong linear correlations were observed between the WEP9 values of the OAs (0.8–21 g P kg−1) and several more easily determined properties, including total P content (r2 = 0.84), organic N content (r2 = 0.82), the sum of Hedley’s more easily dissolved SRP (soluble reactive P) and OP (r2 = 0.95), and the total P and SRP extracted by 16 h of shaking with the bicarbonate reagent (r2 ≥ 0.90). These findings indicate that if greater P availability is desired, the stabilization of biosolids and biowastes should be minimized. These insights into the relationships between OA characteristics and P solubility may benefit the use of OAs in agricultural systems and aid assessments of the environmental significance of their use.

Blue-laser-diode-based high CRI lighting and high-speed visible light communication using narrowband green-/red-emitting composite phosphor film.

We experimentally demonstrate high-speed visible light communication (VLC) and high-quality solid-state lighting (SSL) using polymethyl-methacrylate-doped phosphor film based on cesium lead bromide quantum dot (CsPbBr3-QD) and potassium fluorosilicate K2SiF6:Mn4+, which is excited by a blue gallium nitride laser diode. A 1.6 Gbps data rate is achieved by employing a non-return-to-zero on-off keying modulation scheme. The measured bit error rate of 2.7×10-3 adheres to the standard threshold (3.8×10-3) of forward error correction. Moreover, the generated white-light source has a high color rendering index of 93.8 and a correlated color temperature of 4435 K, and it exhibits a Commission Internationale de l'Eclairage (CIE) 1931 chromaticity coordinate at (0.3556, 0.3520), which is close to the ideal CIE value of white light (0.3333, 0.3333). This work opens up exciting possibilities for future high-speed indoor VLC and high-quality SSL.

A novel redshift mechanism of Ce3+ emission in ZrO2-Ce: YAG composite phosphor ceramics

In this work, ZrO2-Ce: YAG composite phosphor ceramic for the application of high brightness w-LEDs was fabricated for the first time. A novel redshift mechanism of Ce3+ emission is discovered in the composite ceramics that the oxygen vacancy introduced into YAG lattice by the high-temperature reduction of Zr4+ can cause a remarkable non-radiative transition of excited electrons and produce a large redshift from 540 nm to 570 ∼ 610 nm. This kind of redshift has provided a new approach to the supplement of the red component in Ce3+ emission spectra beyond the regular ways of larger rare-earth ions doping or M2+-N4+ double substitution.

Enhancing optical properties of Lu3Al5O12:Ce3+ by cost-effective silica-based photonic crystals

Light-induced interactions between a commercially available green phosphor; Lu3Al5O12:Ce3+ (LuAG:Ce3+); and silica photonic crystals (PC) have been investigated in terms of absorption, excitation- and emission-based properties, respectively. The composites were prepared by embedding the phosphorus and other additives homogeneously in a polymethyl methacrylate (PMMA) matrix in form of thin films. When entrapped in the polymer, the additive-free LuAG:Ce3+ exhibited two efficient absorption bands centered at 346 and 450 nm, respectively. A broadband emission at 538 nm and a Stoke’s Shift of 88 nm were observed when excited by blue light; at 450 nm. When the Ce-free and Ce-doped photonic crystals were utilized along with the LuAG:Ce3+, the emission intensities of the composites were enhanced at 19- and 18-fold with respect to the PC-free forms. Additionally, average decay times of the individual phosphor and silica-modified phosphor composites were measured as 64, 550, 772, and 830 µs, respectively.

Low temperature combustion synthesis and photoluminescence mechanism of ZnO/ZnAl2O4 composite phosphors

ZnO, ZnAl2O4 and ZnO/ZnAl2O4 composite phosphors were prepared by one - or two-step low temperature combustion synthesis method. The ZnO, ZnAl2O4 and ZnO/ZnAl2O4 composite phosphors were obtained by auto-ignited combustion of a carbamide–nitrate precursor gel which is produced by a simple thermally induced redox reaction. The crystalline phase attributes, functional groups, surface morphology, optical and photoluminescence properties of the ZnO, ZnAl2O4 and ZnO/ZnAl2O4 composite phosphors were characterized by X-ray diffraction analysis, fourier transform infrared spectroscopy, scanning electron microscopy, UV–vis spectrophotometer and fluorescence spectrophotometer. The results showed that ZnO/ZnAl2O4 composite phosphors with the type II energy band arrangement were synthesized by two-step low temperature combustion synthesis method. The introduction of zinc oxide into zinc aluminate system improved the crystallinity of zinc oxide and enhanced the optical and photoluminescent properties of the single phase of materials. Based on the energy band theory, the photoluminescence mechanism of ZnO/ZnAl2O4 composite phosphors was proposed.

Moisture resistance, luminescence enhancement, energy transfer and tunable color of novel core-shell structure BaGeF6:Mn4+ phosphor

Recently, Mn4+-doped narrow band red-emitting fluoride phosphors with exceptional luminescence properties have been widely studied for improving the performance of white light-emitting diodes (WLEDs). However, the poor water stability and single luminescent color limit their wider application. Herein, the design idea of new core-shell structure is proposed to improve the properties of BaGeF6:Mn4+ red phosphors by coating poly propylene glycol (PPG) and NaGdF4:Dy3+ nanoparticles. The phase purity, morphology and elemental composition are confirmed via X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The luminescence properties of all phosphors are researched in detail with excitation spectra, emission spectra and fluorescence lifetime curves. PPG coating layer can not only modify the surface defects of the BaGeF6:Mn4+ phosphor to enhance the luminous intensity, but also successfully improve the water resistance of the phosphor. Therefore, BaGeF6:Mn4+@PPG phosphor as red component is more effective for packaging warm WLED. In addition, PPG is considered as the adsorption media layer to connect BaGeF6:Mn4+ phosphors and NaGdF4:Dy3+ nanoparticles. The as-synthesized BaGeF6:Mn4+@PPG-NaGdF4:Dy3+ composite phosphors can emit blue, yellow and red light simultaneously under the excitation of ultraviolet light. The energy transfer processes from Gd3+ to Dy3+ and from Dy3+ to Mn4+ are systematically discussed. By changing the doping concentration of Mn4+ and excitation wavelengths, the photochromic properties of the composite phosphor are successfully realized and the warm white light emission is obtained under the excitation of ultraviolet light. These findings demonstrate that the BaGeF6:Mn4+@PPG-NaGdF4:Dy3+ composite phosphors have more value for practical application.

Effect of Sr on the luminescence properties of Eu3+ activated xZnO-(1-x) SrO-Al2O3 phosphors

Europium-doped xZnO-SrO-Al2O3 (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) phosphors were synthesized by the traditional Solid-State Reaction (SSR) method. The structure of the phosphors prepared was analysed with the x-ray diffraction technique. The xZnO-(1-x) SrO-Al2O3:Eu3+ (0.1 mol%) (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) exhibits varying PL intensity and is maximum for 0.8ZnO-0.2SrO-Al2O3: Eu3+ (0.4 mol%) and hence treated as the most prominent phosphor among these combinations. In the photoluminescence spectrum of the phosphors prepared, a sequence of emission bands were visible at various wavelengths viz., 576, 586, 602, 620, 656 and 702 nm as a result of the transitions of Eu3+ ions [5D0 - 7Fj where (j = 0–4)] and an excitation spectrum at 620 nm. An efficient orange-red phosphor thus developed capable of yielding a quantum efficiency of about 12%. Studies revealed that the commercially available red phosphors having an efficiency of only 9.6% (λex = 394 nm) & 4.2% (λex = 395 nm). Hence the current sample could be an ideal alternative for an efficient phosphor near UV LEDs. The mechanoluminescence of the 0.8ZnO-0.2SrO-Al2O3: Eu3+ (0.4 mol%) phosphor was also measured. The phosphor composition was analysed using XPS. The present paper also reports the thermoluminescence and OSL properties of Europium doped Zinc Strontium Aluminate phosphor at different gamma-ray dosages. Peak shape method was employed to evaluate kinetic parameters like activation energy, frequency factor and symmetry factor.

Eu(III)-doped barium tellurooxyphosphate phosphor with orange-red emission

$${\hbox {Eu}}^{3+}$$ photoluminescence (PL) is studied in the tellurooxyphosphate, $${\hbox {Ba}}_{2}\hbox {TeO} ({\hbox {PO}}_{4})_{2}$$, host. A series of phosphor compositions with varying concentrations of $${\hbox {Eu}}^{3+}$$ dopant in $${\hbox {Ba}}_{2}\hbox {TeO} ({\hbox {PO}}_{4})_{2}$$ are synthesized by high temperature solid-state reaction and the PL spectra are recorded. Under 395 nm wavelength excitation, the emission spectrum shows a single peak corresponding to the non-degenerate transition, $${}^{5} {\hbox {D}}_{0}\rightarrow {}^{7}{\hbox {F}}_{0}$$ indicating that $${\hbox {Eu}}^{3+}$$ preferentially occupies a single crystallographic site. The peak due to the degenerate hypersensitive $${}^{5} {\hbox {D}}_{0} \rightarrow {}^{7}{\hbox {F}}_{2}$$ electric dipole transition of $${\hbox {Eu}}^{3+}$$ in the emission spectrum indicates that the site occupied by $${\hbox {Eu}}^{3+}$$ in the tellurooxyphosphate host lattice is non-centrosymmetric. The CIE coordinate values are $$x = 0.61$$ and $$y = 0.34$$ and are found to be close to the values of the reference phosphor $${\hbox {Y}}_{2} {\hbox {O}}_{3}{:}{\hbox {Eu}}^{3+}$$.

Flexible thin film ceramics for high temperature thermal sensing applications

Yttria Stabilized Zirconia ceramics have been widely used as protective boundary for high temperature environments and flame shields, intrinsic barrier to moisture, and are often considered for extreme environments. This class of materials has the ability to withstand temperatures up to 3000 °C, far exceeding the maximum temperature of operation for most other materials including polymers. Previously, the design of high performing functional materials involving ceramics was limited due to the bulkiness and lack of flexibility of ceramics. However, with the advent of ultra-thin flexible ceramics, it is possible to create thin layered structures that were not previously possible. In this study the authors investigate the potential of 40 μm thin flexible ceramic strips as flame shields for silica aerogels and polydimethylsiloxane phosphor composites. Results show that thermographic phosphors can be excited across multiple layers of YSZ strips, and, their emission characteristics can be accurately detected across multiple layers. Both decay characteristics and amplitude ratio methods were investigated. The YSZ strips provided thermal protection to both aerogels and elastomers. Embedded thermographic phosphor-based temperature measurements were feasible to a depth of at least 120 μm.

Comparative study of the luminescence properties of Ca2+xLa8-x(SiO4)6-x(PO4)xO2:Eu3+ (x = 0, 2) red phosphors

A series of Ca2La8(SiO4)6O2:Eu3+ (CLSO:Eu3+) and Ca4La6(SiO4)4(PO4)2O2:Eu3+ (CLSPO:Eu3+) oxyapatite phosphors have been prepared via traditional solid-state reaction process. The phase composition of phosphors was analyzed by X-ray powder diffraction (XRD), and the morphology was evaluated by scanning electron microscopy (SEM). The characteristic photoluminescence properties were evaluated by analysis of photoluminescence excitation (PLE) and emission (PL) spectra. In addition, the luminescence decay times and emission-temperature relationship were also characterized. The results indicated that the phosphors could be efficiently excited by the near ultraviolet (NUV) light and blue light, and they exhibited red light emission. Meanwhile, the average particle sizes of CLSO and CLSPO hosts are about 2∼8 μm. Moreover, the low symmetry C3 or Cs sites appropriate for Eu3+ in the CLSO and CLSPO hosts are benefit to 5D0 → 7F2 electric dipole transition, which leads to greater R/O values of CLSO:yEu3+ than those of CLSPO:yEu3+. All the obtained results suggested that the prepared phosphors have a potential for application in white light emitting diodes (WLEDs).

Red emission from a novel rare earth free oxide-based CaO–0.5Al2O3–0.5Nb2O5:Mn4+ phosphor with high water-resistance property

A 657 nm red emission from a novel rare earth free oxide-based CaO–0.5Al2O3–0.5Nb2O5:xMn4+ (0.001 ≤ x ≤ 0.008) phosphors with high water-resistance property were prepared by solid-state reaction method. The composition and structure of the as-prepared phosphors was studied. Under relative ultraviolet (331/365 nm) and blue (465 nm) light excitation, the as-prepared phosphor presents a 657 nm red emission that assigned to the 2Eg → 4A2g transition of Mn4+ ions. The red light source in CaO–0.5Al2O3–0.5Nb2O5:Mn4+ system was discussed, and the water resistance property of the phosphor was also investigated. The as-prepared phosphor presents more proper red emission position than those of similar oxide-based Mn4+-activated phosphors and shows excellent water-resistance property compared with commercial used K2SiF6:Mn4+ phosphor. With the further optimization of its photo-luminescent properties, the as-prepared CaO–0.5Al2O3–0.5Nb2O5:Mn4+ phosphors may find its potential application in the field of white LEDs.

Enhanced near-infrared persistent luminescence in MgGa2O4:Cr3+ through codoping

Near-infrared emitting persistent luminescent materials have potential applications in night-vision surveillance and medical imaging. Rational designing of the phosphor composition is of great importance for achieving sufficiently strong and long-lasting persistent luminescence. Herein, a series of MgGa2O4:Cr3+ phosphors with variable concentrations of Cr3+ were prepared via solid state reaction. MgGa2O4:Cr3+ exhibits strong emission in the range from 650 to 800 nm and three excitation bands centered at 275, 420 and 576 nm. With appropriate selection of codopant M (M = Al3+, Si4+, Ge4+ or Sn4+), the MgGa2O4:Cr3+, M phosphor presents remarkably enhanced persistent luminescence. Moreover, the trap distributions were tuned and the number of traps was greatly increased via codoping. In particular, MgGa2O4:Cr3+, Si4+ shows more than 7 h of persistent near-infrared light emission before the intensity drops to 5 × 10−4 mWsr−1m−2. Codoping with appropriate ions provides a good example in optimization and development of persistent luminescent phosphors for potential bioimaging applications.

Efficient full-color emitting carbon-dot-based composite phosphors by chemical dispersion.

Realizing full-color emission plays a key role in exploring the luminescence mechanisms of carbon dots (CDots) and promoting the applications of CDots in light-emitting diodes (LEDs). Herein, a synthesis strategy for full-color emitting CDots was developed through the solvothermal reaction of citric acid and urea with a constant mass ratio but varying reactant concentrations in solvent. With the reactant concentrations increasing, a dual regulation mechanism including an enhanced nucleation growth process and subsequently increased C[double bond, length as m-dash]O/C[double bond, length as m-dash]N-related surface states should be responsible for the photoluminescence (PL) shift of CDots from blue to red. Relying on the hydrolyzation and condensation processes of 3-aminopropyltrimethoxysilane, a simple and universal method was developed by chemically dispersing the CDots into a cross-linked silica network on the surface of SiO2 nanoparticles to produce efficient full-color emitting SiO2/CDot composite phosphors with considerable PL quantum yields in the range of 30-60%. It was proved that the full-color emitting SiO2/CDot composite phosphors could be flexibly applied in packaging white LEDs, releasing pure white light at the Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.33) with a color rendering index (CRI) of 80.4 and a high color-rendering white light coming entirely from CDots with the CIE coordinates of (0.34, 0.36) and a CRI of 97.4, indicating promising application of the full-color emitting SiO2/CDot composite phosphors in the LED field.

Highly efficient and stable CsPbBr3 perovskite quantum dots by encapsulation in dual-shell hollow silica spheres for WLEDs

A highly stable and efficient CsPbBr3@SiO2 composite phosphor is achieved by protecting the CsPbBr3 QDs from direct exposure to the atmosphere by encapsulating CsPbBr3 into dual-shell hollow silica nanospheres.