Ultraviolet Excitation Research Articles

Structural and photometric investigations of green emanating Er3+ activated SrGd2Al2O7 nanophosphors for solid state illumination applications

This study features structural and photometric aspects of a down-converted green emanating erbium (Er3+) activated nanophosphor synthesized via a versatile and environmentally benign urea aided solution combustion procedure. The powder X-ray diffraction pattern (PXRD) of optimal sample SrGd1.96Er0.04Al2O7 studied qualitatively by employing the Rietveld refinement practice, disclosed the tetragonal crystal phase with space group 14/mmm (139), consisting grains of size 50.03 nm. Surface morphology and grain size of nanopowders were well investigated by electron microscopy practices like scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). SEM micrograph gave clear insight that Er3+ doped nanophosphors possess slightly agglomerated particles with pores, voids and cracks due to high pressure breakout of gases while combustion synthesis. TEM and SEM images revealed the size of nanoparticles in the ambit of 40–60 nm which was in coherence with that obtained from the scherrer's equation, while the inter-fringes distance corresponding to diffraction plane (116) was calculated to be 0.27 nm from the HRTEM image. The desired nanophosphor showed brilliant green emission with an intense peak at 551 nm attributed to 4S3/2 → 4I15/2 transition of Er3+ ions, as analyzed through photoluminescent (PL) emission spectra monitored via near ultraviolet excitation wavelength (381 nm) with an optimal doping concentration of 2.0 mol%. Advanced photometric features like CIE color coordinates (0.3017, 0.6043), CCT (6032K), and color purity (76.52%) confirmed their green glow and are found to be in harmony with standard green emission. The study offers a luminous cool green emanating component for the fabrication of WLEDs and advanced optoelectronic appliances.

Eu-MOF fluorescent fiber detector based on polyacrylonitrile: A highly selective and sensitive luminescence sensor for trace amounts of Fe3+

From a medical point of view, Fe3+ cannot be absorbed by the human body and excessive Fe3+ had a complex effect, which could destroy the DNA structure and cause cancer. The detection of Fe3+ in blood had turned into an issue closely related to human health. Herein, Eu(BPDA)1.5phen@PAN fluorescent fibers were successfully prepared by electrospinning using polyacrylonitrile (PAN) as substrate from self-assembled metal organic framework materials (MOFs). In the short response time, the fluorescence quenching phenomenon could be observed by naked eye when excited by ultraviolet light. The functionalized lanthanide Eu-MOF@PAN exhibited a characteristic red light emission dominated by Eu3+ ultra-sensitive electric dipole transition (5D0→7F2) under ultraviolet excitation and strong stability in aqueous solution. Compared with powdered Eu-MOFs, Eu-MOF@PAN had better thermal stability. Eu-MOF@PAN exhibited unique pertinence and excellent sensitivity in the detection of Fe3+, the fluorescence dynamic quenching was deduced by fluorescence lifetime fitting. Compared with the functionalized MOFs previously reported, Eu-MOF@PAN had a lower limit of detection (0.063 μM). This study provided a promising strategy for manufacturing flexible sensors for detecting low concentrations of Fe3+.

Unwrapping the compositional mystery of Eumeninae nest: A laser-induced breakdown spectroscopic study

The nest of Eumeninae wasp is one of nature’s creations, revealing the mysterious architectural beauty through its composition and nanostructuring. The present study unveils the compositional mystery of Eumeninae nest through the signal processing of the laser-induced breakdown spectrum (LIBS). The structure, morphological, and optical characterisations of the nest sample shows nanoparticles of oxides of silicon, aluminium, and iron with an optical bandgap of 2.5 eV, giving a fluorescence emission in the blue region upon ultraviolet excitation. Though, the energy dispersive spectroscopic study confirms the major elements present in the sample, the more elements are revealed through LIBS analysis. The intriguing properties of nest is attributed to the elemental compositions - oxygen, silicon, iron, manganese, chromium, cobalt, calcium and carbon – which necessitate deconvolution of peaks in the spectra for estimating the plasma temperature (4300–5045 K) and electron density (1.13 × 10−19 cm−3).

Multicolor emission in [formula omitted] clusters and Eu3+ activated ZnO–P2O5 glasses achieved under near ultraviolet light excitation

The structural and photoluminescence properties of zinc phosphate glasses activated with Agmn+ clusters and Eu3+ are studied. The addition of Ag+ and Eu3+ does not significantly modify the glassy structural properties evaluated by X-ray diffraction (XRD) patterns and Raman spectroscopy. The only change observed by Raman spectroscopy, is ascribed to the creation of molecular oxygen. The photoluminescence spectra, recorded under near ultraviolet (NUV) light excitation, display the feature broad band attributed to Agmn+ clusters. With the Eu3+ addition, Eu3+ bands located at 578, 591, 611, 652 and 701 nm, appear on the Agmn+ cluster emission, achieving the highest intensity at 0.8 mol% of Eu3+. This behavior is accompanied by a gradual reduction of the Agmn+ cluster emission. Sinks related to Eu3+ absorption on Agmn+ cluster emission and shortening of Agmn+ cluster: S1 → S0 and T1,T2 → S0 emission decays, suggest respectively the existence of radiative and non-radiative energy transfers from Agmn+ clusters to Eu3+. The Burstein model points out that the non-radiative energy transfer processes are predominantly mediated by electric dipole-dipole interaction for the Agmn+ :S1 → S0 transition. The emission tonality, estimated from the CIE1931 chromaticity coordinates and correlated color temperature (CCT) can be tuned from the cold white region to the warm white one, with effective quantum yield measurements up to 48%, depending on the excitation wavelength and Eu3+ doping content. Emission tonalites out of the white light region (orange-pink, purple-pink and pink) are obtained at higher amounts of Eu3+ (0.8 and 1.0 mol%) as well.

Simultaneous excitation at IR and UV of RE3+ triply doped SiO2-Gd2O3 materials for energy conversion purposes

Most traditional photoactive materials for solar cell applications are sensitive to visible light, which highlights the importance of materials that are also active in the ultraviolet (UV) and infrared (IR) regions for an increase in energy conversion efficiency. SiO 2 -Gd 2 O 3 :Er 3+ /Yb 3+ /Eu 3+ (x Er : 0.0–0.3; x Yb : 0.0–1.2; x Eu : 0.0–7.0 mol%) materials were prepared via sol-gel method, followed by thermal treatment at 900 °C for 8 h. The Gd 2 O 3 crystalline cubic structure was determined by XRD and FT-IR, and the lattice parameters were investigated by Rietveld Refinement. Besides, the morphology was observed by SEM micrographs as a system in which Gd 2 O 3 particles are dispersed in SiO 2 . In the EDX spectra. It was registered narrow bands arising from Er 3+ , Yb 3+ , and Eu 3+ doping elements, besides Si 4+ , Gd 3+ , and O 2- , confirming the presence of these elements in the composition. Under IR excitation at 980 nm, the samples showed upconversion phenomena, with Yb 3+ ions working as sensitizers, and effective energy transfer between the doping RE 3+ ions. The emission bands in the visible region are attributed to transitions of Er 3+ ion, and Eu 3+ ion transitions (enhanced up 66 times). Under UV excitation at 247.5 nm, it was observed the down shifting process, seen as narrow bands related to Eu 3+ ion transitions. The samples showed red emission colors as the Eu 3+ concentrations increased in the matrix for upconversion and down shifting process. The results suggest that x Eu : 1.0 mol% is the optimal doping level of Eu 3+ in the SiO 2 -Gd 2 O 3 system. This triply doped sample was simultaneously excited at 980 nm and 247.5 nm. It was observed Eu 3+ and Er 3+ narrow bands in the visible region, responsible for both upconversion and down shifting process when doubly excited. For all these reasons, the materials are promising to be applied to the field of energy conversion and solar cell applications.

Fluorescence of pyrene-doped polystyrene films from room temperature down to 4 K for wavelength-shifting applications

In liquid argon-based particle detectors, slow wavelength shifters (WLSs) could be used alongside the common, nanosecond scale, WLS tetraphenyl butadiene (TPB) for background mitigation purposes. At room temperature, pyrene has a moderate fluorescence light yield (LY) and a time constant of the order of hundreds of nanoseconds. In this work, four pyrene-doped polystyrene films with various purities and concentrations were characterized in terms of LY and decay time constants in a range of temperature between 4 K and 300 K under ultraviolet excitation. These films were found to have a LY between 35 and 50% of that of evaporated TPB. All light yields increase when cooling down, while the decays slow down. At room temperature, we observed that pyrene purity is strongly correlated with emission lifetime: highest obtainable purity samples were dominated by decays with emission time constants of ∼ 250–280 ns, and lower purity samples were dominated by an ∼ 80 ns component. One sample was investigated further to better understand the monomer and excimer emissions of pyrene. The excimer-over-monomer intensity ratio decreases when the temperature goes down, with the monomer emission dominating below ∼ 87 K.

Organic long-persistent luminescence stimulated by visible light in p-type systems based on organic photoredox catalyst dopants.

Organic long-persistent-luminescent (OLPL) materials demonstrating hour-long photoluminescence have practical advantages in applications owing to their flexible design and easy processability. However, the energy absorbed in these materials is typically stored in an intermediate charge-separated state that is unstable when exposed to oxygen, thus preventing persistent luminescence in air unless oxygen penetration is suppressed through crystallization. Moreover, OLPL materials usually require ultraviolet excitation. Here we overcome such limitations and demonstrate amorphous OLPL systems that can be excited by radiation up to 600 nm and exhibit persistent luminescence in air. By adding cationic photoredox catalysts as electron-accepting dopants in a neutral electron-donor host, stable charge-separated states are generated by hole diffusion in these blends. Furthermore, the addition of hole-trapping molecules extends the photoluminescence lifetime. By using a p-type host less reactive to oxygen and tuning the donor-acceptor energy gap, our amorphous blends exhibit persistent luminescence stimulated by visible light even in air, expanding the applicability of OLPL materials.

Green synthesis, structure feature and energy transfer of yellow‐emitting (Y,Gd)2O2SO4:Dy phosphors

AbstractA green chemical precipitation route was used to yield a hydrated basic sulfate precursor upon calcination at 1000°C into a series of (Y,Gd)2O2SO4:Dy particles. The phosphors exhibited characteristic Dy3+ emissions from 4F9/2→6HJ (J = 15/2, 13/2, 11/2) transitions under ultraviolet light excitation; the quenching concentration of Dy3+ was determined to be 2.5 at.%. Substitution of Gd3+ for Y3+ led to an additional strong sharp band at ~277 nm (8S7/2→6IJ transition of Gd3+) in the photoluminescence excitation spectra, upon which the (Gd0.975Dy0.025)2O2SO4 phosphor achieved a ~2.8‐fold higher photoluminescence intensity via an effective energy transfer from Gd3+ to Dy3+ compared with the 354 nm excitation of Dy3+. Both the photoluminescence and photoluminescence excitation intensities of (Y,Gd)2O2SO4:Dy phosphors increased with rising Gd3+ concentration and calcination temperature in the range 750–1000°C. A higher Gd3+ concentration slightly prolonged the effective fluorescence lifetime.

Electron transport in AlGaN/GaN HEMT-like nanowires: Effect of depletion and UV excitation

In this work, we have investigated the features of electron transport in AlGaN/GaN transistor-like heterostructures with nanowires of different width. These nanostructures are studied extensively because of their great electronic and sensing advantages for electronic biosensor applications. We study the depletion effects and impact of ultraviolet excitation on the electron transport in sets of nanowires of different width from 1110 down to 185 nm. We have found significant difference in electrical characteristic’s behavior between wide (1110…480 nm) and narrow (280…185 nm) nanowires and have observed regions related to space-charge-limited transport for the narrowest nanowires. Also, we obtained evident dependence of nanowire’s current-voltage characteristics on the wavelength and energy of UV excitation. External UV excitation allows us to control the depletion widths in nanowires and effectively tune space-charge-limited transport.

A zero-thermal-quenching phosphor Sr3La(AlO)3(BO3)4: Dy3+ for near ultraviolet excitation white-LEDs

The thermal stability of phosphor is a crucial factor for practical white-LED application since phosphor would suffer from emission loss due to non-radiative transition with increasing operational temperature. In this work, a single-host phosphor Sr3La(AlO)3(BO3)4: Dy3+ has been synthesized via high-temperature solid-state reaction method. Interestingly, the phosphor performs prominent zero-thermal-quenching property from 298 K to 573 K, during which the emission intensity rises to 157% at 498 K and remains 138% even at 573 K in comparison that at room temperature instead of decrease. This particular phenomenon could be attributed to the energy transfer and trap mechanism arising from the high temperature. Moreover, under near ultraviolet excitation (352 nm), two main emission peaks located at 488 nm and 580 nm are observed, ascribed to transitions of Dy3+ ion from 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 respectively. Meanwhile, the effect of different Dy3+ content on the luminescence properties is investigated. Among these, 30 mol% of Dy3+ ions is found as the optimum concentration and the phosphor emits white light situated at (0.3298, 0.3786) in CIE coordinates. Based on the zero-thermal-quenching property and near ultraviolet excitation, the as-prepared Sr3La(AlO)3(BO3)4: Dy3+ phosphor can be potential candidates in white-LEDs.

Efficient Broadband Yellow-Green Emission of Vacancy Halide Double Perovskites Through the Ion-Exchanged Strategy.

Broadband high-efficiency luminescent materials have become a hot spot in lead-free perovskite research. There are relatively few broadband yellow-green phosphors with both ultraviolet and blue excitation ranges, which make them more suitable for phosphor-converted white LEDs. Through the ion-exchanged strategy, Cs2Hf1-xTexCl6 (CH1-xTxC) vacancy halide double perovskites were successfully prepared at room temperature. Using different excitation ranges of CH1-xTxC, two types of high-quality white LEDs are obtained. By combining density functional theory calculations and experiments, it is proved that this bright broadband yellow-green emission (photoluminescence quantum yield of 83.46%) is not only derived from the ion transitions of Te4+ but also exhibits the inherent characteristics of self-trapped exciton emission. Our results not only broaden the application fields of lead-free halide perovskites but also provide further insights into the luminescence mechanism.

Photoluminescence properties, excellent thermal stability and energy transfer in Ce3+ and Tb3+ co-doped Sr3Gd2(BO3)4 phosphors

Sr3Gd2(BO3)4: Ce3+, Sr3Gd2(BO3)4: Tb3+ and Sr3Gd2(BO3)4: Ce3+, Tb3+ phosphors were synthesized through conventional high temperature solid state reaction method. Phase purity, crystal structure, photoluminescence properties, and lifetime of the samples were analyzed in detailed. Sr3Gd2(BO3)4: Ce3+ showed a bright blue broad emission band, which was attributed to 4f → 5d transitions of the Ce3+ ions, and it exhibited two broad excitation ranged from 200 nm to 400 nm. For all Sr3Gd2(BO3)4: Tb3+ samples, under ultraviolet excitation bands of 240 nm, four emissions peaked at 490 nm, 544 nm, 585 nm and 623 nm appeared, due to the 5D4 → 7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ions. For the Sr3Gd2(BO3)4: Ce3+, Tb3+ phosphors, the lifetime of the samples were analyzed, which showed the presence of energy transfer between the Ce3+ and Tb3+. The energy transfer efficiency from Ce3+ ions to Tb3+ ions reached 98.37%. When the temperature reached 443 K, the luminescence intensity reached 88% of the initial value. Finally, a white LED was fabricated by using a 365 nm near ultraviolet LED chip combined with BaMgAl10O17: Eu2+ (blue), Sr3Gd0.91(BO3)4: 0.09Ce3+, 1.0 Tb3+ (green), and CaAlSiN3: Eu2+ (red) phosphors. The color coordinates was (0.40, 0.42); correlated color temperature was 3721 K; color rendering index was 91.1. The results showed that the Sr3Gd2(BO3)4: Ce3+, Tb3+ green phosphors were suitable for white LEDs.

Toward efficient photochemistry from upper excited electronic states: Detection of long S2 lifetime of perylene.

A long 0.9ps lifetime of the upper excited singlet state in perylene is resolved by femtosecond pump-probe measurements under ultraviolet (4.96eV) excitation and further validated by theoretical simulations of transient absorption kinetics. This finding prompts exploration and development of novel perylene-based materials for upper excited state photochemistry applications.

Eu3+ and Tb3+ doped LiCaY5(BO3)6: Efficient red and green phosphors under UV or NUV excitations

Eu3+ and Tb3+ are typical red and green-emitting photoluminescent (PL) activators and rare earth borates are well-known good PL hosts. In this contribution, a recently reported borate LiCaY5(BO3)6 was selected as the host to study the Eu3+ and Tb3+ photoluminescence systematically. LiCa(Y1-xEux)5(BO3)6 (0 ≤ x ≤ 1), LiCa(Y1-yTby)5(BO3)6 (0 ≤ y ≤ 1) and LiCa(Y0.88-zTb0.12Euz)5(BO3)6 (0.01 ≤ z ≤ 0.07) were synthesized by solid state reactions and the powder X-ray diffraction proved the high purity and crystallinity by quantifying the unit cell volume expansion when replacing Y3+ with Eu3+ and Tb3+. Charge transfer band and f-f transitions of Eu3+ in ultraviolet (UV) and near UV range are both intense because there exists a strongly noncentrosymmetric site in the host. Concentration quenching effect was also observed at x = 0.30 and 0.50 when excited by CTB and 392 nm, respectively. For Tb3+, strong f-d and weak f-f transitions were observed along with the typical green emission, and the concentration quenching occurs at y = 0.12 and 0.30, respectively. It is interesting to observe the Tb3+ to Eu3+ energy transfer in co-doped phosphors, thus the color tunable emissions from green to yellow, and to red were realized by manipulating the dopant concentrations. A preliminary trial to combine these borates with NUV LED chips gave typical red, green, and warm white lights, indicating the potentials as LED-pumped phosphors.

Luminescent – Superparamagnetic iron oxide nanoparticles functionalized with biomolecules and lanthanides ions. Potential platforms for theranostic applications

This investigation describes the synthesis, characterization, and in vitro cytotoxic evaluation of luminescent-superparamagnetic iron oxide nanoparticles (SPIONs) functionalized with biomolecules and Eu3+ and Tb3+ complexes. They emerge as strong candidates for a large number of biomedical applications, such as drug delivery for bioapplications in therapy and diagnosis (theranostic). Aiming these applications, magnetite nanoparticles (Fe3O4) functionalized with biocompatible ligands, Chitosan (CS) and Glutathione (GSH) and Eu3+ and Tb3+ β-Diketonates complexes were synthesized by a one-step procedure and characterized by different experimental techniques. Regarding bioapplication, their cytotoxicity using the cell viability assay of the blood mononuclear cell fraction were performed. The results show that the cytotoxicity depends on the concentration, nature of ligands and complexes. The SPIONs are luminescent with emission in the visible region under ultraviolet excitation and stable in nanoscale in aqueous medium. They are good candidates as nano-luminescent carriers in biomedical applications.

Optical characteristics of europium and terbium doped strontium orthogermanate phosphors

In this work, europium and terbium activated Sr2GeO4 phosphors were successfully developed by traditional solid state method. Powders XRD, FESEM, EDS, FTIR, DRS and PL techniques have been used to probe the as prepared phosphors. Powder XRD patterns of the phosphors are indexed. The elemental composition of phosphors was obtained from their EDS. FTIR spectra are employed to detect different vibrational groups in phosphor compositions. The DRS profiles of both pristine and Eu3+ (Tb3+) substituted samples exhibit broad and strong band in the 230–370 ​nm region. The photoluminescence studies of europium and terbium doped phosphors exhibited optimistic red emission at 617 ​nm (5D0 → 7F2 of Eu3+ ions) and intense green emission at 543 ​nm (5D4 → 7F5 of Tb3+ ions) upon ultraviolet (UV) excitations respectively. The CIE chromaticity co-ordinates are produced in deep red and green regions. Therefore, these materials may become potential alternatives for red and green phosphors in the display devices and in lamp industry.

Effect Of Nanoparticle Size on The Photoelectrochemical Property of Anatase Nanocrystals in Photocatalysis

Using light energy to make electrochemical reaction, photocatalysis is among the most promising technology for water treatment. In heterogeneous catalysis, electrochemical reactions occur at the liquid/solid of gas/solid interface. The development of materials with a high surface area (nanomaterials) has then been considered as the best route achieving an efficient system. In this paper, we studied the effect of the crystal size on the photoelectrochemical properties of anatase. Two synthesis routes were used to get nanoparticles with different size and the comparison of their efficiency for the degradation of rhodamine B under ultraviolet (UV) light excitation showed that crystallite size is most important than surface area consideration. Comparing results obtained under UV lamp and under sunlight excitation, we also demonstrated that photocatalysis is more efficient under sunlight radiation.

Enhanced luminescence of CsPbBr3 nanocrystals-glass composite scintillators based on Ce3+-doped borosilicate glass

CsPbBr3 nanocrystals-glass composite scintillators based on Ce3+-doped borosilicate glass were prepared by melt-quenching method with further heat-treatment. Incorporating Ce3+ into borosilicate glasses matrix, highly enhanced green emission was observed under 365 nm ultraviolet and X-ray excitation. The transmittance of the prepared CsPbBr3 nanocrystals-glass is as high as 80% at 527 nm, fluorescence lifetime is 21.6 ns, and the luminescent quantum efficiency reaches up to 28% after thermal treatment (550 °C, 12 h). Compared with undoped CsPbBr3 nanocrystals-glass, the X-ray excited luminescence intensity of Ce3+ doped CsPbBr3 nanocrystals-glass is around 190%, which indicates that the issue of absorbing ray energy in glass matrix can be effectively solved by incorporation of Ce3+ ions.

Upconversion Perovskite Nanocrystal Heterostructures with Enhanced Luminescence and Stability by Lattice Matching.

Lead halide perovskite quantum dots (PQDs) exhibit excellent photoelectric and optical properties, but their poor stability and low multiphoton absorption efficiency greatly limit their biological applications. Efforts have been made to combine upconversion nanoparticles (UCNPs) with PQDs to produce a composite material that is NIR-excitable, upconverting, and emission-tunable due to the unique optical properties of UCNPs, which converts tissue-penetrating near-infrared light into visible light based on an upconversion multiphoton excitation process. However, it is challenging to make such a nanocrystal heterostructure and maintain good optical properties and stability of both UCNPs and PQDs because they have different crystal structures. Here, we report the synthesis of heterostructured UCNP-PQD nanocrystals to bring hexagonal-phase NaYF4 UCNPs and cubic-phase CsPbBr1X2 PQDs in close proximity in a single nanocrystal, leading to efficient Förster resonance energy transfer (FRET) from the UCNP to the PQD under NIR excitation, as compared to their counterparts in solution. Moreover, by further improving the lattice matching between the UCNP and PQD using Gd to replace Y, heterostructured CsPbBr3-NaGdF4:Yb,Tm nanocrystals are successfully synthesized, with much enhanced luminescence and stability at high temperatures or in polar solvents or under continuous ultraviolet light excitation as compared to those of the CsPbBr3-NaYF4:Yb,Tm nanocrystals and pure PQDs.

Energy Transfer Mediated Enhancement of Room‐Temperature Phosphorescence of Carbon Dots Embedded in Matrixes

AbstractEnergy transfer (EnT) is a commonly used study method in the research of organic luminescent materials, but rarely reported in carbon dots (CDs) related work. In this work, an efficient EnT mediated method for enhancing room temperature phosphorescence (RTP) of CDs through embedding pure phosphorescent CDs into afterglow matrixes is brought up for the first time. In such design system, the emission intensity, phosphorescence lifetime, and emission time of CDs are prolonged significantly, and all the CD‐based materials emit more than 20 s phosphorescence visible to eye after the ultraviolet excitation. The overlap between the phosphorescence excitation spectra of CDs and the afterglow emission spectra of afterglow matrixes reveal the possibility of the EnT from matrixes to CDs, and the phosphorescence emission and lifetimes spectra of CDs, matrixes, and CDs@matrix further verify the presence of EnT process. Besides, phosphorescent CDs embedded in nonafterglow emission matrixes are also synthesized for analysis and comparison. To employ the outstanding characteristics of the compound of pure phosphorescent CDs and afterglow matrix, advanced information encryption/decryption and rapid fingerprint detection applications are designed. This EnT medicated enhancing RTP strategy provides a new design route to construct the CD‐based material with long phosphorescence emission and high emission intensity.