Maximum Excitation Peak Research Articles

Combustion synthesis and photoluminescence study of novel Sm3+ activated K3La(PO4)2 phosphor for n-UV solid state lighting

In the present study, a novel K3La(PO4)2:Sm3+ phosphor was prepared by the combustion method. The synthesized K3La(PO4)2:Sm3+ phosphor was characterized by XRD, SEM, PL (emission and excitation) and color chromaticity. The recorded X-ray diffraction pattern for the phosphor matches JCPDS no. 00–047–0468. From the SEM analysis, the phosphor had an average particle size of 2–25 micrometers and had a solid microcrystalline structure with specific uneven shapes and aggregation between the crystalline grains. The maximum excitation peak occurs at 403 nm, which corresponds to the 6H5/2→4F7/2 transition of the Sm3+ ions. From all the observed transitions, the emission band at 598 nm (6G5/2→6H7/2) shows an orange-red emission with prominent intensity. The emission intensity of the K3La(PO4)2:Sm3+ phosphor could reach a maximum of 1 mol % and then concentration quenching occurs. Further, concentration quenching is explained using Blasse’s equation and Dexter’s theory. The chromaticity findings of the synthesized phosphor had a CIE coordinate of (0.617, 0.381) and hence might be used for an orange-red emission in solid state lighting.

Blue light‐excitable Eu‐doped yellow emitting borate KSr4B3O9 phosphor for white light‐emitting diodes

AbstractIn the development of novel phosphors for solid‐state light applications, the suitable excitation peak matching with blue LED chip was usually neglected. However, the excitation peak of phosphors was strongly related to the Stocks shift, crystal field splitting, and centroid shift. Here, an environmentally friendly borate phosphor KSr4B3O9: Eu2+ with the maximum excitation peak position at ∼460 nm was prepared in a quite mild synthesis condition. With a blue light excitation, KSr4B3O9: Eu2+ phosphors could emit a bright yellow light centered at ∼560 nm, which could be attributed to the drastic centroid shift and strong crystal field splitting. The strong electron cloud overlaps between Eu–O and the high electron density on the O atom turned out to be the main reason that induces the strong nephelauxetic effect. In addition, the strong crystal field splitting was benefited to the relatively short average Sr–O distance and the large Sr–O distances distribution range from ∼2.23 to 2.96 Å. Meanwhile, the Eu2+ occupation of all the Sr2+ sites in KSr4B3O9 host identified by Rietveld refinement, cryogenic emission spectra, and Eu3+ fluorescent probe gave another evidence to the wide absorption region. The final WLED device and three‐dimensional colorful artwork were fabricated and displayed to suggest a potential application in the solid‐state lighting field and some expressions of esthetic concepts.

Luminescence-enhancement and tunable-excitation of far-red emitting La2LiSbO6:Mn4+, Bi3+ phosphors for plant growth lighting

In this paper, Bi3+ ions were co-doped into La2LiSbO6:Mn4+ phosphors for purpose of improving luminescent properties in the near ultraviolet and blue light range. A significant enhancement from 25.89% to 58.71% in quantum yield under blue light excitation was achieved. Impressively, via increasing Bi3+ concentration, the excitation spectra can be effectively tuned from double to triple bands along with the maximum excitation peak changed. Besides, particle morphology and Raman vibration modes were investigated to reveal the luminescence enhancement and the excitation evolution mechanisms. The results show that Bi3+-induced structure symmetry change may play a dominant role in tunable excitation phenomenon of the samples, which makes La2LiSbO6:Mn4+, Bi3+ may have a potential application in plant growth lighting LEDs for different kind of excitation light sources.

Tunable luminescence between Stark levels of Pr3+:YPO4 nanocrystals by different crystal phase

We report time-resolved second-order fluorescence between Stark levels of 1D2 and 3H4 in Pr3+:YPO4 nanocrystals with different crystal phase. Both intensity ratios of transition peaks between Stark levels and fluorescence lifetimes are modulated by phase composition and dressing effect. We have found that the maximum excitation peak shifts from yellow to orange-red region with continuous phase transformation from hexagonal phase to tetragonal phase, which is attributed to different multi-phonon relaxation rate induced by O–H group in hexagonal phase. The fluorescence lifetimes and intensity ratios of splitting peaks in time domain have also been effectively modulated by choosing excitation frequencies to resonate with different Stark levels. Both wavelength and time tunable luminescence has potential applications in biological labeling, imaging and solid state display devices.

Luminescent properties of BaAl12O19:Tb, Dy phosphors prepared by sol-gel method.

BaAl12O19:Tb, Dy phosphor was prepared by the sol-gel technique using citric acid as a complextant. XRD was used to characterize the relevant crystallization behavior of the phosphor. The luminescence properties and energy transfer between Tb3+ and Dy3+ were investigated. The results revealed that energy transfer exists between Dy3+ and Tb3+ at appropriate Tb3+ concentrations. The emission intensity of Tb3+ increases and energy transfer happens from Dy3+ to Tb3+ ions at the higher content of Tb3+ when Tb3+ and Dy3+ ions were co-doped. BaAl12O19 phosphors doped with Tb3+ or Dy3+ ions only were studied to compared with BaAl12O19:Tb, Dy phosphors. The results showed that the maximum excitation peak of BaAl12O19:Tb is 240 nm and the emission spectrum consists of four peaks at 490, 545, 590, and 625 nm, originating from 5D4 --> 7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ion, respectively. The excitation peaks of BaAl12O19:Dy are at 291, 324 nm and the emissions of Dy3+ are at 370, 447 and 578 nm, originating from 4F9/2 --> 6P5/2, 4F9/2 --> 6H15/2 and 4F9/2 --> 6H13/2 transitions of Dy3+ ion, respectively.

Luminescent properties of tri-cellulose acetate composites doped with rare earth terbium (III) complex

Rare earth terbium (III) ternary complexes were synthesized using acrylic acid (AA) or 5-sulfosalicylic acid (SSA) as the first ligand and 1,10-phenanthroline (Phen) as the second ligand. Tri-cellulose acetate (TCA)/Tb(AA)3Phen or TCA/Tb(SSA)3Phen composites were prepared by means of solution blend, and their luminescent properties were investigated by fluorescence spectrophotometer. The luminescence spectra of TCA/Tb(AA)3Phen and TCA/Tb(SSA)3Phen composites display the characteristic excitation and emission bands of terbium ions and suggest some influence of the TCA matrix on luminescent properties of the terbium complexes. The maximum excitation peak at around 343 nm for the Tb(SSA)3Phen system is redshifted for 14 nm, compared with 329 nm for the Tb(AA)3Phen system, which is correlated to the electron-donating/attractive groups of ligands. In the range of doping concentration of the Tb(AA)3Phen complex (1, 2 and 5 wt.%) or the Tb(SSA)3Phen complex (1, 2, 3 and 5 wt.%), emission intensities increase with the increment of corresponding doping concentration and concentration quenching effect has not taken place.

Preparation and functionalization of a visible-light-excited europium complex-modified luminescent protein for cell imaging applications

Lanthanide complex-based luminescent bioprobes have shown great utility in a variety of time-resolved luminescence bioassays, but these bioprobes often require UV excitation and suffer from problems related to bioaffinity and biocompatibility for in vivo applications. In this work, a new visible-light-excited europium(III) complex with the maximum excitation wavelength over 400 nm, BHHBB-Eu(3+)-BPT {BHHBB: 1,2-bis[4'-(1'',1'',1'',2'',2'',3'',3''-heptafluoro-4'',6''-hexanedion-6''-yl)-benzyl]-benzene; BPT: 2-(N,N-diethylanilin-4-yl)-4,6-bis(pyrazol-1-yl)-1,3,5-triazine}, has been synthesized for the preparation of an artificial luminescent protein that can be used as a visible-light-excited luminescent bioprobe for cell imaging. By encapsulating BHHBB-Eu(3+)-BPT into apoferritin with a simple dissociation-reassembly method, the luminescent protein, Eu@AFt, with a maximum excitation peak at 420 nm and a long luminescence lifetime of 365 μs was fabricated and successfully used for visible-light-excited time-resolved luminescence cell imaging. Moreover, by conjugating a mitochondria-targeting molecule, (5-N-succinimidoxy-5-oxopentyl)-triphenylphosphonium bromide (SPTPP), onto the surface of Eu@AFt, a mitochondria-specifically-tracking luminescent probe, Eu@AFt-SPTPP, was further prepared and used for visible-light-excited confocal luminescence microscopy imaging to visualize the mitochondria of living cells.

A New Red-Emitting La1–xPrxSr2AlO5 Phosphor Powder Prepared by Combustion Synthesis

New red luminescent powders of La(1-x)Pr(x)Sr2AlO5 (x = 0.01 at.) were prepared by the combustion synthesis method. Microstructural properties were characterized by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The La(1-x)Pr(x)Sr2AlO5 X-ray diffraction pattern revealed a tetragonal phase. Morphology of the grains showed nanobars with sizes of approximately 550 nm in length. Photoluminescence, cathodoluminescence and diffuse reflectance were analyzed in detail. Photoluminescence revealed two narrow emission peaks located at lambda(em1) = 497 nm (green) and lambda(em2) = 620 nm and a single maximum excitation peak of lambda(ex) = 287 nm. The cathodoluminescence spectrum confirmed the peaks detected by photoluminescence analysis. The absorbance spectrum showed broad absorption with a maximum around lambda = 280 nm, which agrees with the maximum excitation peak detected by photoluminescence.

Optical Properties of Blue-Light-Emitting (Ca,Sr)Mg2Si3O9:Eu2+ Phosphor

For light-emitting diode (LED) excitation at 400 nm, the optical properties of a Eu2+-activated CaO–SrO–MgO–SiO2 material system were investigated. All the materials were synthesized by solid state reaction. In particular, (Ca,Sr)Mg2Si3O9:Eu2+, which has the same crystal structure as CaMgSi2O6, was found to be promising as a blue-light-emitting phosphor for near UV LED application. The luminance intensity was optimized by controlling the Eu2+ concentration and the composition of the host lattice. The ratio of calcium ions to strontium ions was a convenient parameter for adjusting the maximum excitation peak to 400 nm, which is favorable for near UV LED excitation. The highest luminance intensity of Ca1-x-ySryMg2Si3O9:Eux2+ under 405 nm excitation was achieved at the Eu2+ concentration of x=0.01 and a Sr2+ concentration of y=0.3. The luminance intensity of (Ca,Sr)Mg2Si3O9:Eu2+ was found to be superior to that of a commercial blue-light-emitting BaMgAl10O17:Eu2+ phosphor, which is used for near-UV LED excitation.

Photoluminescence Enhancement Effect of CeO2 in Rare Earth Composites MM′O3/CeO2 and MM′O3/CeO2: Pr3+ (M = Ca, Sr; M′ = Ti, Zr)

In the context, a modified sol-gel technology was afford to the synthesis of rare earth composite ceramic phosphors MM'O(3)/CeO(2) and MM'O(3)/CeO(2): Pr(3+) (M = Ca, Sr; M' = Ti, Zr) with multicomponent hybrid precursors were composed. The micromorphology, particle size and photoluminescence properties were studied with XRD, SEM and luminescent spectroscopy in detail. Both XRD and SEM indicated the particle sizes were in the submicrometer range of 100-300 nm. The photoluminescence for these ceramic phosphors were studied in details with the different component of host (molecular ratio of Sr, Ca and Ti, Zr), presenting a broad spectral band in the visible blue-violet region with the maximum excitation peak at 449 nm and a wide emission range with a maximum peak at 619 nm, which was ascribed to be the characteristic transition of Pr(3+) ((1)D(2) --> (3)H(4)). These phosphors can be expected for visible light conversion (blue --> red) materials. Especially it can be found that the introduction of CeO(2) can enhance the luminescence intensity of MM'O(3) and MM'O(3): Pr(3+).

In situ Sol—Gel Composition of Inorganic/Organic Polymeric Hybrid Precursors to Synthesize Red‐Luminescent CaTiO3:Pr3+ and CaTi0.5Zr0.5O3:Pr3+ Phosphors.

AbstractFor Abstract see ChemInform Abstract in Full Text.

In situ sol–gel composition of inorganic/organic polymeric hybrid precursors to synthesize red-luminescent CaTiO 3:Pr 3+ and CaTi 0.5Zr 0.5O 3:Pr 3+ phosphors

In this paper, rare earth coordination polymers with aromatic carboxylic acids were used as the precursors of luminescent species, composed with polyethylene glycol (PEG) to achieve inorganic/organic hybrid polymeric dispersing media. The resulting multicomponent hybrid precursors were assembled by an in situ sol–gel process of tert- n-butyl titanate (Ti(OC 4H 9) 4) and further thermal decomposed to obtain two series of rare earth oxysalts phosphors: CaTiO 3:Pr 3+ and Ca(Ti 0.5Zr 0.5)O 3:Pr 3+. Both XRD and SEM indicated the particle sizes of them were in the range of around 1 μm. The excitation spectra presented a broad spectral band in the visible blue-violet region with the maximum excitation peak at 445 nm, while no apparent absorption appeared in ultraviolet region. The corresponding emission spectra showed a wide emission range with a maximum peak at 619 nm, which was ascribed to be the characteristic transition of Pr 3+ ( 1D 2 → 3H 4), which can be expected for visible light conversion materials.

Initiation mechanism of the photo-degradation of poly(vinyl chloride)

To elucidate the initiation mechanism of the photodegradation of PVC, luminescence and ultra-violet spectra of PVC film and model compounds (3-chloro-2-butanone(I), 1-chloro-2-butene(II) and 2-butanone(III)) assumed to present in PVC were measured. Neat PVC film showed a fluorescence spectrum with a peak at 360 nm (a maximum excitation peak at 296 nm). The intensity of the peak decayed rapidly and new additional peaks appeared in the longer wavelength region. The new peaks which were ascribed to conjugated double bonds increased in intensity and shifted during the photo-irradiation. None of the model compounds showed fluorescence and II showed no phosphorescence. The phosphorescence of PVC was very similar to that of I, and its intensity decreased rapidly during the photo-irradiation. The phosphorescence spectrum of III was very weak and similar to that of photo-irradiated I. Among the products of the photolysed 3-chloro-2-butanone, III was detected by GC-mass spectrometry. The number of chlorine atoms evolved from I was much higher than that from II. The results obtained suggest that for the initiation of the photodegradation of PVC, allylic C-Cl does not necessarily play so important a role as α-chloroketone structures.

A microfluorescent PAS method for the quantitative demonstration of cytoplasmic 1,2-glycols.

Fluorescent microspectrophotometry using dichroic mirror vertical epi-illumination of tissue sections stained with the PAS reaction (periodic acid and pararosaniline Schiff reagent) provides a measure of the relative concentration of 1:2 glycols within and between tissue sections. In PAS reacted sections of agarose gel, pararosaniline Schiff fluorescence increases linearly as the concentration of agarose increases (r=0.97, p less than 0.05). The concentration of glycogen within liver as measured by a phenol-based tissue assay is linearly correlated with pararosaniline Schiff fluorescence of formalin fixed liver sections (r-0.87, p less than 0.05). These relationships are unaffected by alcian blue or hematoxylin. Heretofore the amount of color reaction as measured by densitometry at the pararosaniline absorption peak was claimed to be an unreliable indicator of the amount of reactive glycol present in tissue. Our observations indicate that when the concentration of Schiff reagent exceeds an empiric limit relative to available polysaccharides, the Schiff reagent-tissue complex reflects light at the excitation wavelength instead of fluorescing the emission spectra. This can be circumvented by using dilute pararosaniline-Schiff reagent, shorteining the staining period, and lowering the temperature of the staining medium. While routine PAS staining reactions are followed by washing in running water to develop the red color seen with broad spectrum illumination, water development is unnecessary for the dye-tissue complex to fluoresce. The fluorescent emission peak and the maximum excitation peak of both developed and undeveloped pararosaniline-Schiff-reagent-tissue complexes are 645--50 nm and 540--45 nm, respectively. These spectral characteristics are not changed by binding to oxidation products of different glycoproteins or polysaccharides. Intense exposure to room light, but not 100 repetitive short (0.13 s) exposures, causes partial photodecomposition. Quantitative assessment of cytofluorescence requires definition of the optical system used to measure emission. In the microspectrophotometer employed in this study, dichroic mirrors reflect light with variable efficiency depending on wavelength from the light source to the stage, and variably block light reflected or emitted from the specimen, serving as crude barrier filters. These dichroic mirror characteristics are influenced by the exact nature of the optical coating on the surface of each individual mirror. Since the optical coating on the surface of each individual mirror. Since the optical coating of similar mirrors may vary, the properties of individual mirrors must be considered in the interpretation of spectral data and in determining the proper optical conditions for quantification of cytofluorescence.