Decrease In Luminescence Intensity Research Articles

Structural and luminescent behaviour of Dy(III) activated Gd3Al5O12 nanophosphors for white-LEDs applications

Single-phased cool white light emissive Gd3-xAl5O12:xDy3+ (x = 0.01–0.07) nanophosphors have been prepared via gel-combustion method. Diffraction data and Rietveld results have affirmed the development of a single cubic phase of all the prepared samples with space group Ia-3d (230). Furthermore, the crystallite size was calculated through Debye-Scherrer's formula and the Williamson-Hall method. In the EDX spectrum, the nonappearance of peaks analogous to the foreign elements affirms the pure synthesis of the considered phosphors. TEM observation reveals agglomerated porous crystalline material with non-uniform shapes and varying particle size in 20–80 nm range. Fourier Transform Infrared (FTIR) spectroscopy has been applied for the examination of chemical bonding with other vibrational characteristics. The luminescence study confirms the intense blue and yellow emission of synthesized phosphors at 482 nm and 576 nm respectively owing to 4F9/2→6HJ (J = 15/2, 13/2) transitions. Moreover, the detailed evaluation of the concentration quenching process established that dipole-quadruple interaction is answerable for the decrease in luminescence intensity after optimum dopant ion concentration. The chromatic analyses recommend that emission from the optimized nanophosphors lies in the region of cool white light. The outcomes of the present investigation propose that Gd3Al5O12:Dy3+ phosphors might be a potential candidate for white-LEDs applications.

Rare-Earth-Doped Barium Molybdate Up-Conversion Phosphor with Potential Application in Optical Temperature Sensing.

A BaMoO4:[Er3+]/[Yb3+] up-conversion (UC) phosphor was synthesized by co-precipitation and calcination of the precursor at 800 °C. The main peak (112) for the synthesized phosphor was strongly detected in the XRD pattern and had a tetragonal structure. The doping of rare-earth ions affected the crystal lattice by shifting the main peak, decreasing the lattice constant, and shifting the position of the Raman signal. The synthesized upconverted phosphor exhibited strong green signals at 530 and 553 nm and weak red signals at 657 nm when excited at 980 nm. The green light emission intensity of the UC phosphor increased as the pump power of the laser increased due to the two-photon effect. The synthesized upconverted phosphor was prepared as a pellet and flexible composite. Thermal quenching led to a decrease in luminescence intensity as the temperature increased, which means that the phosphor can be applied to optical temperature sensing.

Pre-diagnosis of Failure Spots in Orange AlInGaP Light-Emitting Diodes Soaked in Liquid Nitrogen Using Machine Vision and Multiple Optical, Electrical, and Material Characterizations

In this study, Pre-diagnosis of degraded aluminum indium gallium phosphide (AlInGaP) light-emitting diodes (LEDs) that were soaked in liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) was performed. To visualize the early deterioration of LED emission, a combination of material, electrical, optical, and computer-aided machine-vision analysis of LED failure spots on the surface was examined. Results indicate that several small failure spots, which can be identified by the MATLAB processed emission images and surface roughness variation, can be found. Furthermore, LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> soaking induced some local damages inside the device that penetrate the multiple-quantum well. The decrease of current and luminescence intensity also reflects the gradual degradation of the device after being soaked in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . This integrated analysis and Pre-diagnosis of the degraded device provided early screening of LED failure spots and real-time inspection during operations.

Structural and optical analysis of YAl3(BO3)4: Pr3+ phosphors for lighting applications

A series of Pr3+ activated YAl3(BO3)4 phosphors were fabricated by solid-state reaction technique and they were characterized via phase, morphology and photoluminescence studies. Powder X-ray diffraction peaks were suitably matched to JCPDS No. 72–1978. The presence of various vibrational bonds was identified using Fourier transform infrared spectroscopy. High resolution scanning electron microscopic investigations show that the phosphor particles were distributed uniformly and presented a rod-like shape. The photoluminescence results show that the studied phosphors were easily excited by visible wavelength to produce intense-yellow to pale-yellow tunable emission. The decrease in luminescence intensity and lifetime was assigned to dipole-dipole interaction energy-transfer among excited Pr3+ ions. Observed results show that the 0.05 mol% of Pr3+ activated phosphor produce intense-yellow luminescence at 480 nm excitation.

Surface Coverage- and Excitation Laser Wavelength-Dependent Luminescence Properties of U(VI) Species Adsorbed on Amorphous SiO2

Time-resolved luminescence spectroscopy is usefully used to identify U(VI) surface species adsorbed on SiO2. However, the cause of the inconsistent luminescence lifetimes and spectral shapes reported previously remains undetermined. In this study, the U(VI) surface coverage (Γ) and excitation laser wavelength (λex) were examined as the predominant factors governing the luminescence properties of U(VI) surface species. At neutral pH, the luminescence lifetimes of U(VI) surface species increased with decreasing Γ. In the low-Γ region, where a relatively large number of adjacent surface sites are involved in the formation of multidentate surface complexes, the displacement of more number of coordinated water molecules in the equatorial plane of U(VI) results in a longer lifetime. The pH-dependent luminescence lifetimes of U(VI) surface species at the same U(VI) to SiO2 concentration ratio in the pH range of 4.5–7.5 also explain the effect of the surface binding sites on the luminescence lifetime. The time-resolved luminescence properties of the U(VI) surface species were also investigated at different excitation wavelengths. Continued irradiation of the SiO2 surface with a UV laser beam at λex = 266 nm considerably reduced the luminescence intensities of the U(VI) surface species. The higher the laser pulse energy, the greater the decrease in luminescence intensity. Laser-induced thermal desorption (LITD) of U(VI) surface species is suggested to be the origin of the decrease in luminescence intensity. LITD effects were not observed at λex = 355 and 422 nm, even at high laser pulse energies.

Bromine speciation by a paper-based sensor integrated with a citric acid/cysteamine fluorescent probe and smartphone detection

The present work reports on a sensitive and affordable non-instrumental method for the determination of bromine species in environmental waters by combination of paper-based headspace sampling and smartphone-based fluorescence detection. The proposed approach takes advantage of the luminescence quenching of a probe (5-oxo-3,5-dihydro-2 H-thiazolo[3,2-a]pyridine-7-carboxylic acid, TPCA) derived from natural compounds, namely, citric acid and cysteamine, when exposed to molecular bromine. The decreased luminescence intensity of the probe was attributed to the formation of a dibrominated derivative of TPCA at the detection area of a paper-based analytical device (PAD). Remarkably, PADs modified with the luminescent probe showed excellent stability. Under optimal conditions, the proposed approach showed limits of detection of 5.4 µg L-1 and 0.9 µg L-1 for Br- and BrO3-, respectively, with a repeatability lower than 10% for both bromine species. The non-instrumental method was validated against two certified reference materials, namely BCR-611 and BCR-612 (low and high level Br- in groundwater), and successfully applied to the analysis of environmental water samples with recoveries in the range 93–106%.

Luminescence investigations on Dy3+ doped CdO-PbF2 phosphate glass-ceramics

• P 2 O 5 – CdO – PbF 2 -SrO – Dy 2 O 3 glass and the corresponding glass-ceramics were prepared. • Existence of PbF 2 crystallites and their structural confirmations were done by X-ray diffraction studies. • Effect of heat treatment on luminescence was discussed. • Decrease in luminescence intensity in presence of nanocrystals in glass ceramics was reported This paper reports the structural and photoluminescence investigations on Dy 3+ doped transparent CdO-PbF 2 phosphate glass/glass ceramics with SrO. Upon heat treatment, the nanocrystals occurred in glass ceramics are spherical in shape in the sizes of 10nm to 20nm. The luminescence intensities were strongly dependent on nanocrystallinity and showing the same kinetics as efficient luminescent hosts. In the present host, well incorporation of Dy 3+ ions in nanocrystals and low energy transfer to Dy 3+ ions due to existence of other crystalline phases, both the mechanisms occurred. The consequent variations in luminescence intensities also observed.

Facile synthesis and characterization of ZnO, ZnO:Co, and ZnO/ZnO:Co nano rod-like homojunction thin films: Role of crystallite/grain size and microstrain in photocatalytic performance

Herein, to investigate the photodegradation of methylene blue (MB) under UV light irradiation and the photocatalytic activity of chemically derived ZnO, ZnO: Co 5% nano rod-like thin films and ZnO/ZnO: Co 5% homojunction, the role of grain size and microstrain on their structural, optical, electrical and photocatalytic properties were studied. Hexagonal wurtzite structure, the doping of Co2+ into ZnO host lattice, reduced crystallite/grain size, and enhanced microstrain have been confirmed by structural and morphological analysis. The presence and the atomic content of Zn/Zn2+, Co/Co2+, O/O2- elements, and ions have been confirmed by EDS and XPS measurements. The n/p-type conductivity in nano rod-like film and p-n bilayers have been verified by Hall and I-V characterizations. The PL analysis showed that the decreased luminescence intensity and the formation of defect/trapping centers by Co2+ doping and formation of p-n homojunction as crystallite/grain size decreased while microstrain increased. With 5% Co-doping and the emergence of p-n homojunction, the photocatalytic efficiency (ղ %) was reduced compared with parent ZnO photocatalyst, while the crystallite/grain size decreases and microstrain enhances. The decreased ղ % was attributed to the reduced crystallite/grain size, increment of microstrain, and the generation of defects/trapping centers via 5% Co-doing and formation of ZnO/ZnO:Co 5% nano rod-like homojunction. These results demonstrate that the fabrication of p-n homojunction will not always result in an enhanced ղ % even if it puts down the recombination of light-induced charge transporters.

SORPTION-LUMINESCENT DETERMINATION OF OROTIC ACID IN MEDICINAL DRUGS

Luminescent properties of orotic acid (vitamin B13), known bioactive substance, have been evaluated in this research. It has been shown that inside a coordination complex of orotic acid with terbium (III) an intermollecular excitation energy transfer from a ligand to a lanthanide ion occurs which causes sensitization of terbium (III) ion luminescence. Intensity of the terbium (III) ion luminescence (ILum) increases in the presence of anionic and cationic surfaceactive agents as a result of displacement of water molecules from coordination sphere of the complex. As a consequence of this process, a non-radiative deactivation of excitation energy decreases and more efficient excitation energy transfer from a ligand to a lanthanide ion occurs. It has been established that after absorption of analyte of interest onto a polymer matrix of a solid phase extraction sorbent with subsequent increasing of its molecular rigidity more efficient excitation energy transfer is observed followed by elevation of luminescence (ILum) intensity of the coordination complex being studied. Intensity of luminescence of coordination complex of orotic acid with terbium (III) in the form of a sorbate salt has been estimated involving different types of sorbents (Phosphalugel, SFG-75, Calflo E, Celite 545, Silicagel Merck). Most suitable results have been achieved by the use of Silica gel Merck as a solid-phase matrix (sorbent). The removal rate of the complex from the solution in this case reaches to 97%. The most effective conditions for determination of orotic acid have been specified. The highest values of luminescence intensity is obtained by conducting of sorption using 5 mL of solution and 100 mg of sorbent. Luminescence intensity of the complex in the form of a sorbate salt, during a sorption process, increases in presence of ethonium, cationic dimeric surface-active agent. Decrease in luminescence intensity of the complexes in the form of a sorbate salt in presence of other surface-active agents may be caused by solubilization of the complex in the solution and thereby reduced level of its sorption. On the basis of presented research work a new analytical procedure has been developed for the solid-phase luminescence determination of orotic acid and orotic acid salts in pharmaceutical drugs. Determination of orotic acid salts has been performed in pharmaceutical drugs ‘Magnerot’ (magnesium orotate) and ‘Potassium orotate’. The proposed analytical procedure for determination of orotic acid salts is remarkable by good metrological characteristics and relative simplicity of performance. The relative standard deviation, Sr, is 3,6 - 4,3%.

Effects of crude oil and aromatic compounds on growth and bioluminescence of Vibrio campbellii FS5.

Fifteen native luminescent bacteria were isolated from the Gulf of Thailand, and their sensitivity for the detection of toxicity of crude oil and its aromatic components was investigated. Of these isolates, Vibrio campbellii strain FS5 was one of the two most highly inhibited bacteria at all crude oil concentrations. This bacterium showed a decrease in luminescence intensity of between 10.7 and 80.2% after a 15-min exposure to 0.0001-10mg/L of crude oil. The degree of bioluminescence inhibition increased with increasing concentrations of crude oil. The presence of crude oil at all concentrations had negative effects on the log bioluminescence per log number of viable cells after 15- to 105-min exposure. About 10 to 100 times, lower half maximal effective concentration (EC50) values were observed for polycyclic aromatic hydrocarbons (PAHs) than those for benzene, toluene, ethylbenzene, and xylene (BTEX). In the presence of each individual BTEX and PAH, the bioluminescence inhibition increased with increasing exposure time (1-32h). This indigenous bacterium can be used as a simple and general indicator of oil contamination and its impact on coastal waters as well as for assessing potential toxicity during oil bioremediation.

Creating a human-induced pluripotent stem cell-based NKX2.5 reporter gene assay for developmental toxicity testing

To test large numbers of chemicals for developmental toxicity, rapid in vitro tests with standardized readouts for automated data acquisition are needed. However, the most widely used assay, the embryonic stem cell test, relies on the counting of beating embryoid bodies by visual inspection, which is laborious and time consuming. We previously developed the PluriBeat assay based on differentiation of human induced pluripotent stem cells (hiPSC) that we demonstrated to be predictive for known teratogens at relevant concentrations using the readout of beating cardiomyocytes. Here, we report the development of a novel assay, which we term the PluriLum assay, where we have introduced a luciferase reporter gene into the locus of NKX2.5 of our hiPSC line. This enabled us to measure luminescence intensities instead of counting beating cardiomyocytes, which is less labor intensive. We established two NKX2.5 reporter cell lines and validated their pluripotency and genetic stability. Moreover, we confirmed that the genetically engineered NKX2.5 reporter cell line differentiated into cardiomyocytes with the same efficiency as the original wild-type line. We then exposed the cells to valproic acid (25–300 μM) and thalidomide (0.1–36 µM) and compared the PluriBeat readout of the cardiomyocytes with the luminescence intensity of the PluriLum assay. The results showed that thalidomide decreased luminescence intensity significantly with a higher potency and efficacy compared to the beating readout. With this, we have developed a novel hiPSC-based assay with a standardized readout that may have the potential for higher throughput screening for developmental toxicity.

Highly luminescent and electrically conductive hybrid material

We proposed a highly luminescent and electrically conducting polymer composite material based on polylactide acid (PLA) polymer filled with reduced graphene oxide (RGO) or graphene oxide (GO) nanoplatelets covered by organic Eu(III) complexes tris-dibenzoylmethane mono-1,10-phenanthroline europium(III) [Eu(DBM)3Phen]. No Eu(DBM)3Phen luminescence quenching by RGO and GO nanoplatelets has been observed in emission decay. Partial luminescence intensity decrease is caused by graphene nanoplatelets absorption. Conductivity of the composite film is increased by more than five orders of magnitude as compared to the pure polymer. The proposed material is suitable for 3D printing technology and wide applications in optoelectronics.

New europium complexes and their use in red light-emitting diodes and vapoluminescent sensors

Three novel trivalent europium [Eu(III)] complexes – Eu(DBM)3Phen-Ph-Ph, Eu(DBM)3Phen-mCF3-Ph, and Eu(DBM)3Phen-pCF3-Ph – were designed, synthesized, and characterized using various spectroscopic methods. Then their photophysical characteristics were investigated. The Eu complexes in the solid phase showed a pure red emission (due to the electric dipole transitions of the Eu3+ ion). In a solution, they had multiple emissions due to their ligand contribution. The solvatochromism studies revealed that the Eu(III) complexes in the methanol and DMSO solutions had both metal ion and ligand emissions with similar intensities, which yielded a white emission. Of all the Eu(III) complexes, Eu(DBM)3Phen-mCF3-Ph showed the best quantum yield. In addition, the fluorinated mCF3 ligand had an unusually high lifetime value. Its remarkable linear decrease in luminescence intensity with increasing temperature opens a new window for its use as a sensitive temperature sensor at the 30–80°C range. The CIE color coordinates of the fabricated red LEDs (InGaN) are very close to the standard NTSC CIE color coordinates for bright red emissions, and the color purity as well as the LER values of the fabricated red LEDs are also very good. The Eu(III) complexes exhibited on-off photoluminescence switching via the vapoluminescent process and responded best to the acid-base (HCl-NH3) vapors. All these features suggest that the synthesized Eu(III) complexes are efficient candidates for red-emitting LEDs and vapoluminescent sensors. Organic chromophores, which are phenanthro-imidazole ligands based on fluorinated moieties coordinated with Eu(III) metal ions, very efficiently facilitate energy transfer from the ligand to the Eu(III) ion. The CIE color coordinates of the complexes showed a bright pure red emission, with x = 0.66 and y = 0.33 (612 nm). The fabricated light-emitting diode (LED) showed superior color quality and the complexes showed on-off-on luminescence behavior after exposure to the acid-base vapors.

Luminescent Porous Silicon Filled with Nanoscopic Magnetic Structures – Assessment of the Optical and Magnetic Properties

Luminescent porous silicon which is denoted as microporous silicon (LPSi) offers a structure size of a few nanometers. The pores are arranged in a branched network-like morphology. These structures are filled with magnetic metals resulting in a composite system with specific optical and magnetic properties. In this work Ni and Co, respectively are used. The luminescence is observed in the red-orange region due to the small structure size. The photoluminescence spectra of initial LPSi offer a peak around 620 nm, which is blue-shifted after Ni-filling with increasing deposition time and the intensity of the luminescence is increased. In the case of Co deposition the spectrum is adequate but with increasing metal filling the luminescence intensity decreases. Magnetic field dependent measurements performed for easy and hard axis magnetization show a high magnetic anisotropy between these two magnetization directions, even more pronounced in the case of Co. The magnetic response of the samples is related to the interconnected pores and differs significantly to mesoporous silicon filled with magnetic nanostructures.

Effect of micro-/mesoporous structures on H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; sensing ability of YVO&lt;sub&gt;4&lt;/sub&gt;:Eu&lt;sup&gt;3+&lt;/sup&gt; phosphor particles

YVO4:Eu3+ phosphor particles are proposed as an H2O2 sensing material based on their turn-off luminescence. The YVO4:Eu3+ particles having various surface microstructures were synthesized through liquid processes and their H2O2 sensing ability was evaluated by immersing them in an aqueous H2O2 solution with a constant volume at a fixed concentration. The microstructures were characterized in detail not only by electron microscopy but also by nitrogen adsorption to elucidate factors governing the H2O2 sensing ability. It was then indicated that micro-/mesoporous structures, which were introduced in the micrometer-scaled spherical particles during their synthesis by a biphasic sol–gel method, were a decisive factor for achieving the effective H2O2 sensing. The YVO4:Eu3+ particles synthesized under the improved condition could show a 37% decrease of luminescence intensity after the H2O2 treatment.

Specific Features of Photoluminescence of CH3NH3PBI3 Perovskites Synthesized on Nanostructured TiO2 Surface

The influence of nanostructured titania surface on the photoluminescence of organometallic perovskite CH3NH3PbI3 films is studied. It is found that the CH3NH3PbI3 luminescence intensity and lifetime decrease on the TiO2 surface, which testifies to charge transfer from perovskite to titania. Charge transfer occurs most efficiently for perovskite films synthesized on the surface of mesoporous TiO2 films. The time dependence of magnetic effect on the luminescence of CH3NH3PbI3 on mesoporous TiO2 films is related to the recombination luminescence caused by forward and backward electron transfer between perovskite and titania.

Structural, optical and magnetic properties of Y3−0.02−xEr0.02Yb x Al5O12 (0 < x < 0.20) nanocrystals: effect of Yb content

The paramagnetic Y3−0.02−x Er0.02Yb x Al5O12 (x = 0.02, 0.06, 0.10, 0.12, 0.18, 0.20) nanocrystals (NCs) were synthesized by the microwave-induced solution combustion method. The XRD, TEM and SEM techniques were applied to determine the NCs’ structures and sizes. The XRD patterns confirmed that the NCs have for the most part a regular structure of the Y3Al5O12 (YAG) phase. The changes of the distance between donor Yb3+ (sensitizer) and acceptor Er3+ (activator) were realized by changing the donor’s concentration with a constant amount of acceptor. Under 980 nm excitation, at room temperature, the NCs exhibited strong red emission near 660 and 675 nm, and green upconversion emission at 550 nm, corresponding to the intra 4f transitions of Er3+ (4F9/2, 2H11/2, 4S3/2) → Er3+ (4I15/2). The strongest emission was observed in a sample containing 18% Yb3+ ions. The red and green emission intensities are respectively about 5 and 12 times higher as compared to NCs doped with 2% of Yb3+. In order to prove that the main factor responsible for the increase of the upconversion luminescence efficiency is reduction of the distance between Yb3+ and Er3+, we examined, for the first time the influence of hydrostatic pressure on luminescence and luminescence decay time of the radiative transitions inside donor ion. The decrease of both luminescence intensity and luminescence decay times, with increasing hydrostatic pressure was observed. After applying hydrostatic pressure to samples with e.g. 2% and 6% Yb3+, the distance between the donor and acceptor decreases. However, for higher concentrations of the donor, this distance is smaller, and this leads to the effective energy transfer to Er3+ ions. With increasing pressure, the maximum intensity of near infrared emission is observed at 1029, 1038 and 1047 nm, what corresponds to 2F5/2 → 2F7/2 transition of Yb3+.

Luminescence modulation of the Eu3+ doped Srn+1SnnO3n+1 (n=1, 2, 5, ∞) ceramics based on photochromism and its application in anti-counterfeiting technology

The structure and optical properties of Srn+1SnnO3n+1 ceramics greatly depend on the n value. Thus, we fabricated four compositions, namely Srn+1SnnO3n+1:Eu3+ (n = 1, 2, 5, ∞) ceramics, and their crystal structure, photoluminescence, photochromism and luminesce modulation properties have been investigated. It is found that excellent photochromism and luminesce modulation properties are found in Sr2SnO4:Eu3+ and Sr3Sn2O7:Eu3+ ceramics. After 280-nm light irradiation, the Sr2SnO4:Eu3+ ceramics transform into gray purple from primal white. Meanwhile, luminescence intensity decrement ratio ΔIdec of the colored Sr2SnO4:Eu3+ reaches a high value of 80.8% under optimized irradiation wavelength. The decreased luminescence intensity of Eu3+ can be completely recovered via 450-nm light irradiation. The ΔIdec of Sr3Sn2O7:Eu3+ ceramic reaches 53.1%, and the decreased luminesce intensity can not be covered by light irradiation, only can be covered by a high temperature stimulus at 400 °C. Finally, we successfully fabricated a flexible membrane using Sr2SnO4:Eu3+ and PDMS for anti-counterfeiting applications.

Synthesis process dependent white LPL in Zn2GeO4 ceramic and the long afterglow mechanism

The white long persistent luminescence (LPL) material Zn2GeO4 ceramic was prepared by high temperature solid-state method. It is the first time to report the afterglow can last for more than half an hour, and the color does not change with time delay. Such a long afterglow time is enough for photocatalysis research. The structure, luminescence and afterglow properties were analyzed by X-ray diffraction, fluorescence spectra and afterglow decay curves. It is the first time to find the dosage ratio of Zinc Oxide (ZnO) to Germanium Oxide (GeO2) and the annealing temperature affect the crystal phase and optical properties of the products. These two aspects were studied in detail. It was found that GeO2 played the role of fluxing agent in the reaction system because of its low melting point. The amount of GeO2 must be more than the stoichiometric amount because it has a low boiling point and can volatilize at high temperature. Too high sintering temperature and much excessive GeO2 led to crystallization of Zn2GeO4 ceramic during cooling process. The experimental results showed that the initial afterglow spectrum ranged widely from 400 nm to 700 nm after the sample was excited by 254 nm UV light and this broad band could be fitted to three or four Gaussian curves. The Gausses fitted curves peak at 450 nm, 510 nm, 590 nm and 680 nm. It is concluded that the white light is a combination of these light peaking at different wavelength and each peak corresponds to different defects inside the material. The internal defects are decreased a lot because of ceramic crystallization. As a result, the luminescence intensity and afterglow intensity decrease with the decrease of defects, but the afterglow time is not affected.

Towards a white-emitting phosphor Ca10V6O25 based material

To achieve a stable material capable of white-light emission, we fabricated Ca10V6O25 by both co-precipitation (CP) and microwave-assisted hydrothermal (MAH) methods at different temperatures. The effects of structural disorder at a short-range (Raman spectra), medium-range (UV–vis spectra), and long-range (X-ray diffraction) on the material structure and its effect on optical properties were investigated. Both CP and the MAH methods were efficient for obtaining pure Ca10V6O25 material with different morphologies. Significant changes in morphology and degree of structural order and disorder were found to affect the photoluminescence (PL) properties. All samples exhibited a broadband PL spectrum, characteristic associated to charge transfer processes of the [VO4]3- group, as well as transitions that occurred in the energy levels located within the band gap. The samples obtained by the MAH method at temperatures of 100 °C and 120 °C exhibited a lower structural disorder (at long- and short-ranges), the CIE chromaticity coordinates were located in the white region, MAH100 (x = 0.311 and y = 0.348) and MAH120 (x = 0.350 and y = 0.368). Furthermore, we conducted a detailed study of temperature dependence of PL spectra. All samples displayed decreased luminescence intensity as temperatures increased and low values of activation energy (approximately 2 meV). Finally, the as-synthetized Ca10V6O25 material has interesting properties for possible applications as a white-emitting phosphor under ultraviolet excitation.