Al Phosphor Research Articles

Interface induced photoluminescence enhancement from heterojunction BaMoO4/HEAs phosphors: Experiment, theory and anti-counterfeiting application

The BaMoO4/FeCoNiCrMo (BMO/HEA(Mo)), BMO/FeCoNiCrTi (HEA(Ti)) and BMO/FeCoNiCrTiAl (HEA(Al)) phosphors were synthesized by an integrated technology. The structural characterization showed that except the main lattice phase, only the characteristic peak of high-entropy alloys (HEAs) appeared in BMO/HEAs phosphors and the existence of lattice distortion for [MoO4]2- in BMO. The microstructure analysis confirmed that there is a special interface contact between BMO and HEAs, which makes the metal in HEAs easy to have a certain connection with BMO, which causes the lattice distortion of [MoO4]2- to intensify, thus accelerating the recombination rate of charge carriers in BMO/HEAs phosphors. The BMO/HEAs phosphors have a strong emission peak at 445 nm under the excitation wavelength of 285 nm. Theoretical calculations and experiments confirmed that the luminescence of BMO/HEAs phosphor is caused by the lattice distortion of [MoO4]2-, the interface defect of BMO/HEAs and the recombination of charge carriers. The Mo in HEA(Mo) can accelerate the recombination rate of charge carriers between BMO and HEAs, thus enhancing the luminescence performance of BMO/HEA(Mo) phosphor and exhibit dynamic fluorescence anti-counterfeiting applications. However, the Ti in HEA(Ti) and Al in HEA(Al) can easily separate the charge carriers between BMO and HEAs, thus reducing the luminescence of BMO/HEA(Ti) and BMO/HEA(Al) phosphors.

Blue-excited red emission of CeO2:Eu3+, Al3+ cubic phosphor: Influence of Al3+ ion doping and Judd-Ofelt theory

In this work, a series of CeO2: 0.1 Eu3+, xAl3+ (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 mol %) red phosphors could be efficiently excited with blue-light was successfully prepared by solid-state reaction. The X-ray diffraction confirmed the formation of a single-phase CeO2 cubic with high crystallinity. Under blue light (466 nm) excitation, the CeO2: Eu, Al phosphors showed dominant red emission of Eu3+ ions associated with 5D0 – 7F2 transition, which matched well with the commercial blue light InGaN chip. Significantly, the red emission intensity of sample co-doped with 0.3% mol Al3+ was enhanced by 8-times compared to the un-doped one. This result was caused by the presence of Al3+ ions forming oxygen vacancies and disturbing the symmetry of the host, leading to effectively enhanced red emission of the system. The enhanced red emission mechanism of the CeO2:Eu3+, Al3+ phosphors was further explained by Judd-Ofelt (J-O) theory analysis and radiative properties, including branching ratios (βr), transition probability (A), radiative lifetime (τcal), and stimulated emission cross-section (σe) of the phosphor were determined. The CeO2:0.1Eu3+, 0.3Al3+ phosphor shows intense red emission, a long lifetime (0.735 ms), and high quantum efficiency (49.46%), making it a suitable candidate as a red component for preparing low-cost WLEDs.

Effect of synthesis route on the photoluminescence properties of SrTiO3:Pr,Al phosphor: Nanoparticles and microcubes

Sr0.998Pr0.002Ti0.998Al0.002O3 phosphors were prepared by hydrothermal (HT) and polymeric precursor (PP) methods. PP sample exhibits broadening of X-ray diffraction peaks due to the higher surface region of nanoparticles compared to HT sample. X-ray absorption spectroscopy results depicted defects associated with the formation of TiO5 octahedra for HT sample, which is ascribed to the rapid crystallization process in HT synthesis of the mesocrystals with cube-like shape. A quenching of 4f → 4f emissions in Pr3+ ions and a broad spectrum are observed for HT sample, which are attributed to structural disorder in the forming and modifying lattice due to charge compensation between Sr-O11 and Sr-O12 (or TiO5 and TiO6) clusters and intermediate levels in band gap states.

SrTiO3:Pr,Al phosphor mesocrystals: The role of Al-doping in short-range and electronic structure and its influence on photoluminescence properties

Phosphor materials with narrow emission bands and high quantum efficiency have received a good amount of attention, suggesting the possibility of several applications in the field of optoelectronic devices. SrTiO3:Pr is an example of a material with these characteristics. In this study, mesocrystal samples of Sr0.998Pr0.002Ti1−yAlyO3 (SrTiO3:Pr,Al) were prepared via a hydrothermal route, and the morphology presented a microcube shape and pristine structure with Pm3m space group without any spurious phases for all Al concentrations. Measurements of X-ray absorption spectroscopy (XAS) at Ti K-, LII,III-, and O K-edges, calculated projected density of states, and Raman spectroscopy revealed that the hydrothermal method and Al incorporation cause a local symmetry breaking, deviating from the cubic structure, Ti off-center displacement, tilting of TiO6 octahedra, and O vacancies. As the Al content increases, the intensity of some emissions in the photoluminescence spectra also increases up to 3 at%. The disorder produced by Al concentration leads to a lower symmetry around Pr3+ sites, resulting in an increase in the probabilities of transitions for Pr3+ ions due to the mixing of the opposite parity in 4 f configurational levels. On the other hand, higher Al concentrations cause a decrease in the intensity of Pr emissions, which is related to their quenching because of O vacancies. Additionally, intrinsic defects due to the hydrothermal route and Al incorporation generate a broad emission in the photoluminescence spectra. This broad emission is associated with intermediary electronic levels in the band gap caused by these intrinsic defects.

Experimental and theoretical studies of red emission enhancing mechanism in Al-doped CaMoO4:Eu phosphor

In this work, a complete picture of the relationship between the structural and optical properties of Al-doped CaMoO4:Eu phosphor was investigated empirically and theoretically. A series of Al-doped CaMoO4:Eu phosphors were synthesized by solid-state reaction. X-ray diffraction analysis and Rietveld refinement confirmed the formation of a single-phase tetragonal CaMoO4. Under the excitation wavelength of 395 nm, the phosphors exhibited typical red emission bands of Eu3+ as a function of Al3+ doping contents and reached a maximum value at 0.1 mol % Al3+. In addition, the CaMoO4:0.05Eu, 0.1Al phosphor showed chromaticity coordinates (0.6406, 0.3370), which is close to the pure red color as standardized by the National Television System Committee. Significantly, the red emission intensity of Al-doped CaMoO4: 0.05Eu phosphor was 5-times higher than that of the undoped one. This enhancement was explained by Judd-Ofelt (JO) analysis, from which intensity parameters (Ωλ, λ = 2, 4) and radiative properties including branching ratios (βr), transition probability (A), radiative lifetime (τcal), and stimulated emission cross-section (σe) of the phosphor were derived. Judd-Ofelt analysis confirmed that Al3+ promotes the covalent character in the Eu–O bond and the asymmetry in the CaMoO4 crystalline structure. The CaMoO4: 0.05Eu, 0.1Al phosphor generates strong red emission and possesses high values of branching ratio (81.80%), emission cross-section (102.3×10−22 cm2) and quantum efficiency (48.44%) and is potential for low-cost WLED applications.

Far-red-emitting LaSrRO4:Mn4+ (R = Al and Ga) phosphor: Synthesis and optical properties

LaSrRO4:Mn4+ (R = Al and Ga) are prepared by the high-temperature solid-phase method in air. Their luminescence properties, crystal structure, concentration dependent spectra, time-resolved spectra, fluorescence lifetime, and luminous mechanism are systematically researched, respectively. Mn4+ ion is the luminescence center of LaSrRO4:Mn4+ (R = Al and Ga). The excitation spectra of LaSrRO4:Mn4+ (R = Al and Ga) under monitored at 715 nm lie in the range 210 – 650 nm with two main excitation peaks at ∼360 nm and 520 nm. With the excitation at 360 and 520 nm, LaSrRO4:Mn4+ (R = Al and Ga) emit far-red light and have the emission spectra covering the region from 650 to 800 nm due to the 2Eg → 4A2g transition of Mn4+ ions. The ideal Mn4+ concentration in LaSrAlO4:Mn4+ and LaSrGaO4:Mn4+ are ∼ 0.4 mol% and 0.6 mol%, respectively. The spectral properties of samples verify the crystal field s via the Tanabe-Sugano energy level diagram of Mn4+ ion. LaSrRO4:Mn4+ (R = Al and Ga) have the emission spectra match with the absorption spectra of the plant photosensitive pigments red light and far-red light, which infers their promising application in plant growth light-emitting diode (LED) lamp

Regulating photoluminescence behavior by neighboring-cation-size in Sr8CaX(PO4)7: Eu2+ (X = Al and Ga) phosphors for high color rendering solid-state lighting source

The photoluminescence behavior in a multiple cation lattice host for obtaining desired spectral emission is an important scientific question to develop next-generation high quality lighting sources. However, how to manipulate the distribution of rare-earth activators over various cation sites is still a technical challenge. Herein, for the first time, trivalent ions Al3+ and Ga3+ were introduced to β-Ca3(PO4)2-kind host for preparing the new isostructural Sr8CaAl(PO4)7 (SCAP) and Sr8CaGa(PO4)7 (SCGP) hosts and controlling the incorporation of activators Eu2+ in the M(4) sites. Their structural evolution, morphology, diffuse reflection spectrum, electron structure and luminescent properties were systemically investigated. The emission of Eu2+ ions distributed over the nine-coordinated Sr(1, 3, 5)O9, eight-coordinated Sr(2)O8 and special coordinated Sr(4)O6 sites was located in the green (507 nm), yellow (555 nm) and red (610 nm) regions, respectively. Further, a smaller cation radius (Al3+) allowed higher number of activators (Eu2+) to be accessed to the neighboring M(4) lattice site for obtaining more intense red emission, which would enable these kinds of phosphors-converted white light emitting diodes to show quite high color-rendering indexes (Ra = 94.4). This neighboring-cation-size strategy mentioned here can become a novel approach to PL spectral modulation through controlling the distribution of Eu2+ activators over various lattice sites for excellent solid state lighting.

Luminescence enhancement of La4Ti9O24:Eu3+ red-emitting phosphors via cation-substitution of M (Ga, Nb, Ta, Zr, Al) ions

Eu3+- and M (Ga3+, Nb5+, Ta5+, Zr3+, Al3+)-co-doped La4Ti9O24 phosphors were prepared by the solid-state reaction method. The structural phase formation, luminescence properties, and possible LED-lighting application were investigated. The undoped La4Ti9O24 shows an indirect transition with a band-energy of 2.88 ​eV La4Ti9O24 has a broad intrinsic emission band (350–700 ​nm) peaked at 530 ​nm (2.34 ​eV) at 300K. Eu3+-doped La4Ti9O24 presents red luminescence from 5D0→7FJ (J ​= ​0, 1, 2, 3, 4) transitions, which was obviously enhanced with the cation-substitution of M (Ga3+, Nb5+, Ta5+, Zr3+, Al3+) on Ti4+ sites in the lattices. The typical thermal quenching of La3.72Eu0.28Ti8.55M0.45O24 (M ​= ​Al) phosphor is ΔE ​= ​0.342 ​eV. Importantly, the optical excitation of the samples fit well with the commercial LED-chip because of its efficient absorption in near-UV region (395 ​nm) and blue (465 ​nm) wavelength region. The red-LED device packaging with the optimal phosphor was achieved, which has a luminous efficiency of 42 lm/W with a working current of 200 ​mA and a testing voltage of 3.2 ​V. The experiments suggest that the phosphor could be potential for solid-state LED-lighting and display.

Design and Discovery of Nitride Phosphors with Unique Properties

Inorganic luminescent materials, acting as color converters, play key roles in solid state lighting. Among a large quantity of phosphors, nitride phosphors have attracted great attentions as they show promising photoluminescence properties (i.e., high conversion efficiency of blue light, thermally robust, and abundant emission color). With advances in solid state lighting techologies, phosphors with desired properties are reuiqred, which is thus necessary to search for appriporate phosphors. In this presentation, we will introduce two nitride phosphors, Sr2AlSi2O6N:Eu2+ and La2.9Si6-x Al x N11-x/3:Ce3+. Sr2AlSi2O6N:Eu2+ was predicted by using high-throughput calculations, and synthesized in a gas-pressure sintering furnace at 1400oC. The crystal structure of Sr2AlSi2O6N (space group: P4̅21m) was derived from Ba2ZnGe2S6O (ICSD no. 14174) via a multispecies substitution of Ba2+ with Sr2+, Zn2+ with Al3+, Ge4+ with Si4+,S2− with O2−, and O2− with N3−. This phosphor showed a super-broad emissin band spaning from 400 to 850 nm and a full-width at half maximum (fwhm) of 230 nm, under 330 nm excitation. The super-broad emission was ascribed to the structural disorder of Si/Al and O/N. Combined with a UV LED, Sr2AlSi2O6N:Eu2+ enabled to produce a white LED with superior color quality (Ra = 97, R9 = 91). La2.9Si6-x Al x N11-x/3:Ce3+ (LSN:Ce,Al) was designed by applying the interstitial site engineering strategy, i.e., partially substituting Si by Al. The introduction of Al in the lattice created a new site for Ce3+, leading to an additional red emission (λ em = 600-665 nm). The origin of this red emission was assigned from the first-principles calculation to the Ce3+ ion occupying the [Si8N8] void in the c~1/2 layer, of which the calculated transition energies matching with experiment within 0.1 eV. Such an interstitial Ce3+ site was created as a charge compensator for the aliovalent substitution of Si4+ by Al3+ ions. The red-enhanced LSN:Ce,Al phosphor showed great potentials for improving the optical quality (i.e., color temperature and color rendition) of laser-driven white light.

Comparison and study of the preparation methods for phosphor layer in nuclear battery

This work investigated the preparation and optimization of phosphor layer for radioluminescent nuclear battery, and analyzed the property change of the phosphor after irradiation. ZnS:(Cu, Al) with grain size of 5 μm was selected as the phosphor material, and AlGaInP semiconductor was used as the photovoltaic unit. Monte Carlo modeling was used to simulate energy deposition, absorbed dose, penetration of β particles in the phosphor. The optimized coupling scheme of radioisotope sources and phosphor layer was obtained based on comparison particle penetration depth and the output power of radioluminescent nuclear battery. The phosphor layer with 60Co γ-radiation enhanced the luminescence property up to 50% at the radiation dose of 871 kGy, which is considered as an optimized method of phosphor layer preparation. The radiation of 10 MeV electron was conducted to study the degradation based on the microscopic lattice characteristics, morphological changes, optical and electrical properties. Phosphors have excellent radiation resistance. The output power of nuclear batteries has only declined by 43% even when electron radiation dose reaches 8.56 MGy. The prospect for utilizing ZnS:(Cu, Al) phosphor as radiant energy conversion materials in nuclear battery was also discussed. Results provided an effective guideline for predict the service conditions of radioluminescent nuclear battery.

気相合成法ZnS:Ag, Al蛍光体における深欠陥密度の低減化

気相合成法ZnS:Ag, Al蛍光体における深欠陥密度の低減化

Opto-impedance spectroscopy and equivalent circuit analyses of AC powder electroluminescent devices.

High energy photons can affect the dielectric response of AC powder electroluminescent devices (ACPELDs). In this paper, electroluminescent (EL), phosphor and dielectric films are photo-excited at peak wavelengths of 399 nm, 520 nm and 625 nm to identify the dielectric relaxation processes occurring in ACPELDs. The 399 nm illumination changes the frequency-dependent dielectric responses of both EL and phosphor films due to the photo-induced excitation of ZnS:Cu,Al phosphor particles. A higher illumination intensity increases the dipolar polarization in the resin matrix and enhances the Maxwell-Wagner-Sillars (MWS) effect at the particle/resin interfaces. Equivalent circuits relating to the relaxation processes present in the EL and phosphor films are derived. From the analyses of the circuit component values, a charge generation and accumulation process is proposed to explain these opto-impedance behaviors.

Optimization of processing parameters for designing an efficient AC driven powder electroluminescent device

This paper reports various critical processing parameters for the development of efficient ZnS doped with Cu, Al phosphors optimized to exhibit AC electroluminescence. Different firing atmospheres and temperatures were used for the synthesis of electroluminescent phosphor materials. As synthesized ZnS: Cu, Al phosphor powders were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Photoluminescence (PL) and Electroluminescence (EL) spectroscopy studies. Average crystallite size calculated from XRD lies in a range of 44–49µm and average grain size as revealed by SEM lies in the range 3–5µm. The results showed that the phosphor powders have hexagonal phase and exhibit near band edge luminescence in the blue region. This is one of very few reports that depict the observation of EL from hexagonal ZnS:Cu,Al phosphor system. Polycrystalline powders emit PL in a broad band with a maximum at 2.53–2.74eV above the valence band. The PL spectrum of the ZnS:Cu,Al phosphor showed emission peaks at 453nm, 467nm, 485nm and 490nm that could be attributed to the generation of deep level energy traps. The prototype of an alternating current driven thick (40±2µm) film EL device has been fabricated and the threshold voltage was observed to be around 95–120V at a frequency of 1kHz. The critical processing parameters for designing an efficient EL device have been highlighted and discussed thoroughly in the current paper.

Synthesis and luminescence properties of novel red phosphors LiRGe2O6:Mn4+ (R = Al or Ga)

LiRGe2O6:xMn4+ (R = Al or Ga) (0 ≤ x ≤ 1.0 mol%) phosphors are synthesized by solid-state reaction method in air, and their crystal structures, luminescence properties, and fluorescence lifetimes are investigated. Their photoluminescence (PL) bands peaking at ∼ 670 nm owing to the 2E → 4A2 transition of Mn4+ ion cover the region from 620 to 750 nm (λex = 289 nm), and photoluminescence excitation (PLE) bands (λem ≈ 670 nm) are observed in the range of 200–550 nm. With excitation 289 nm, PL intensity of LiAlGe2O6:0.6%Mn4+ phosphor is far stronger than that of LiGaGe2O6:0.6%Mn4+ phosphor owing to the influence of crystal field. The optimal Mn4+ ions concentration is ∼0.6 mol%. The fluorescence lifetime and quantum efficiency of LiAlGe2O6:0.6%Mn4+ and LiGaGe2O6:0.6%Mn4+ phosphors are ∼1.55 ms, 68.5 μs, 32%, and 15%, respectively. Luminous mechanism, the temperature quenching mechanism, and the influence of crystal field to luminous properties are analyzed and discussed, respectively. The experiment results are helpful to develop other novel Mn4+-doped phosphors.

Plasmachemical modification effect on luminescence of AIIBVI phosphors

We investigated the effect of processing conditions in low-temperature plasma on luminescent characteristics of AIIBVI phosphors. As a result of treatment, the luminescence spectra of all tested phosphors shifted to longer wavelengths, which was caused by change of quantities of luminescent centers due to the redistribution (diffusion) of the activator in the crystal lattice. In the case of ZnS:Cu,Cl and ZnS:Cu,Al phosphors brightness increased as a result of treatment. Therefore when phosphors were plasma coated with protective MgO encapsulation both brightness and stability were improved at the same time.

Effect of plasmochemical modification on electro-optical and surface properties of zinc sulfide electroluminescent phosphors

Method for improving the brightness of photo- and electroluminescence from ZnS:Cu and ZnS:Cu, Al phosphors by their treatment in a low-temperature gas-discharge plasma was developed. The relationship between the luminescence brightness and spectra and surface properties of the phosphors was studied. The mechanism of processes that occur on the surface and in the bulk of phosphor particles during their bombardment with plasma ions was determined.

Luminescence properties of stoichiometric EuM2S4 (M = Ga, Al) conversion phosphors for white LED applications

AbstractEuM2S4 (M = Ga, Al) phosphors were synthesized using the solid‐state reaction method. The structure and photoluminescence (PL) properties of the phosphors were investigated in detail. XRD pattern results indicated that the two phosphors are isostructures to the orthorhombic structure. The PL spectra showed that the EuGa2S4 and EuAl2S4 phosphors can be excited efficiently by UV–visible light from 350 to 480 nm and that they emit intense green and bluish‐green light, with emission bands peaking at 545 and 506 nm, respectively. The fluorescence lifetimes of Eu2+ were calculated to be 0.076 and 0.064 µs for EuGa2S4 and EuAl2S4, respectively. The thermal quenching temperature was 412 K for EuGa2S4. A green LED was fabricated by the combination of a near‐UV InGaN chip and the prepared EuGa2S4 phosphor. The EuGa2S4 phosphor exhibits much better green color purity than EuAl2S4. As a result, EuGa2S4 might be a promising green phosphor candidate for solid‐state lighting LED technology.

Effects of annealing on 320 nm cathodoluminescence from hexagonal boron nitride powders

AbstractThe effect of annealing in various atmospheres (N2, H2, NH3 O2 and vacuum) on the 320 nm emission bands of hexagonal boron nitride (h‐BN) powders has been investigated by cathodoluminescence (CL). The CL intensity was decreased by annealing in the N2, H2and NH3 atmospheres at 1200 °C, with H2and NH3 having more effect than N2. On the other hand, the annealing in the O2 atmosphere increased the CL intensity remarkably at annealing temperatures higher than 800 °C. These results suggest that the oxygen located near the particle surface is related to the enhancement of the 320 nm bands in h‐BN. The highest CL intensity, which was obtained at an annealing temperature of 900 °C, reached to about one third of that measured for ZnS:Cu,Al phosphor under the same measurement conditions. The investigation of the powder annealed at higher temperatures in a vacuum indicated that the luminescent centers responsible for these emission bands are thermally stable up to about 1300 °C (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Vacuum Ultraviolet Photoluminescence Properties of (Y,Gd)VO4:Eu,Al Phosphors Synthesized by Ultrasonic Spray Pyrolysis

not Available.

Solid-state image converters on the basis of the GaAs/ZnS structures

Emission-voltage characteristics and frequency dependences of the luminescence intensity of electroluminescent capacitors on the basis of the ZnS:(Cu,Al) phosphor are studied. The effect of X-ray radiation (17 keV) on the high-resistivity GaAs layers obtained by three methods is studied. The possibility to develop the detectors of the ionizing radiation with optical reading of information with the use of the GaAs/ZnS structures is shown using a mathematical simulation. It is noted that the most promising material for the development of the solid-state image converters is GaAs:Cr obtained by diffusion of Cr from the deposited layer.