Changes In Photoluminescence Spectra Research Articles

Photoluminescence of L-Valine Irradiated with Small Doses

The measurement technique and the results obtained by optical spectroscopy during excitation of L-valine molecules by photons described. The photoluminescence spectra of L-valine studied in the wavelength range 400-700 nm during excitation by photons of different energies 3.26-4.51 eV. Peculiarities were found in the luminescence spectra (radiation intensity, positions of maxima), indicating the excitation of the OH, CO and CH molecules as fragments of the valine molecule by photon impact. The same results obtained for the samples of L-valine irradiated by electrons with the dozes 0.2, 0.5, 2 and 5 Gy. Irradiation of L-valine leads to fragmentation of carboxyl COOH group. The biggest changes in photoluminescence spectra observed for the sample with 0.2 Gy irradiation doze. Also X-ray powder diffraction spectra measured, which showed absence of any structural changes for the irradiated samples. The results (photoluminescence and XRay structural spectra) of melted at 330o C L-valine sample are presented.

Effect of gamma-irradiation on the photoluminescence of silver-doped lithium triborate glass.

Optical-luminescence properties, including absorption spectra, photoluminescence excitation spectra, and changes in photoluminescence spectra after irradiation with γ-rays in the dose range of 1-3Gy, were measured for novel L i B 3 O 5:A g dosimeter glass. A clear dependence of the intensity of the photoluminescence (PL), with a maximum of approximately 300nm, on the dose value when excited by light with λ e x c =220n m was observed. The mechanism of PL in γ-irradiated L i B 3 O 5:A g glass is proposed to be a consequence of radiation annihilation with the emission of relaxed exciton-like electronic excitations with the participation of impurity defects (A g 0) in the glass structure. Considering that L i B 3 O 5 has an effective atomic number of Z e f f =7.39, which is the closest to Z e f f =7.42 of human body tissue, L i B 3 O 5:A g glass can be very promising for γ-dosimetry in medical practice during radiation therapy of patients with cancer. The presence of lithium Li(6) and boron B(10) isotopes increases the sensitivity of L i B 3 O 5:A g glass to neutrons, which is promising for the manufacture of individual neutron dosimeters for applications in a new field of radiation therapy-neutron therapy.

Study on photoluminescence properties of Er2O3 materials as irradiation damage and temperature sensors

Photoluminescence (PL) properties of Er2O3 specimens were examined by using visible lasers (532 nm and 635 nm) and a UV LED light source (365 nm) to investigate the applicability for irradiation damage monitoring of materials in fusion reactors. Both in the laser induced and UV light induced PL spectra, green (510–590 nm) and red (630–725 nm) luminescence was observed. In the spectrum measurements on specimens with different crystallinities, it was confirmed that an intensity of the red luminescence weakened significantly compared with that of the green luminescence in an Er2O3 specimen with a lower crystallinity. The results indicate that the PL measurements of Er2O3 materials could be applicable for the irradiation damage monitoring in fusion reactors. The luminescence property of ion beam irradiated Er2O3 showed that information of irradiation damages could be kept up to ∼ 300 ℃ and almost recovered at 700 ℃. Based on the obtained luminescence properties, positions in a fusion reactor where Er2O3 materials could be used as irradiation damage sensors are proposed. Changes in PL spectra at high temperatures up to ∼ 400 ℃ indicate the possibility that the Er2O3 materials might be applicable also for temperature monitoring of in-vessel components during reactor maintenance periods.

The high-pressure structural evolution of ErVO4 investigated by photoluminescence spectroscopy

• The high pressure photoluminescence spectra of ErVO 4 were collected up to ∼ 35 GPa. • The changes of photoluminescence spectra indicate the existence of three phase transitions upon compression. • ErVO 4 experiences zircon to scheelite to fergusonite to post-fergusonite phase transition sequences. • Scheelite-type ErVO 4 is recovered after pressure release. The phase stability of ErVO 4 was investigated by photoluminescence spectroscopy up to ∼ 35 GPa. The changes in spectra at ∼ 7.9 GPa, ∼20 GPa and ∼ 31 GPa suggest the existence of three phase transitions upon compression. With comparison to related rare earth orthovanadates, we suggested ErVO 4 experiences zircon to scheelite to fergusonite to orthorhombic Cmca phase transition sequences. Our study provides the photoluminescence signature for various polymorphs of ErVO 4 , which will refine our understanding of the structural behavior of rare earth orthovanadates.

Rational Design of Surface-State Controlled Multicolor Cross-Linked Carbon Dots with Distinct Photoluminescence and Cellular Uptake Properties.

We disclose for the first time a facile synthetic methodology for the preparation of multicolor carbon dots (CDs) from a single source barring any chromatographic separations. This was achieved via sequential intraparticle cross-linking of surface abundant carboxylic acid groups on the CDs synthesized from a precursor to control their photoluminescence (PL) spectra as well as affect their degree of cellular internalization in cancer cells. The change in PL spectra with sequential cross-linking was projected by theoretical density functional theory (DFT) studies and validated by multiple characterization tools such as X-ray photoelectron spectroscopy (XPS), PL spectroscopy, ninhydrin assay, etc. The variation in cellular internalization of these cross-linked CDs was demonstrated using inhibitor assays, confocal microscopy, and flow cytometry. We supplemented our findings with high-resolution dark-field imaging to visualize and confirm the colocalization of these CDs into distinct intracellular compartments. Finally, to prove the surface-state controlled PL mechanisms of these cross-linked CDs, we fabricated a triple-channel sensor array for the identification of different analytes including metal ions and biologically relevant proteins.

Chemical Control of the Dimensionality of the Octahedral Network of Solar Absorbers from the CuI-AgI-BiI3 Phase Space by Synthesis of 3D CuAgBiI5.

A newly reported compound, CuAgBiI5, is synthesized as powder, crystals, and thin films. The structure consists of a 3D octahedral Ag+/Bi3+ network as in spinel, but occupancy of the tetrahedral interstitials by Cu+ differs from those in spinel. The 3D octahedral network of CuAgBiI5 allows us to identify a relationship between octahedral site occupancy (composition) and octahedral motif (structure) across the whole CuI–AgI–BiI3 phase field, giving the ability to chemically control structural dimensionality. To investigate composition–structure–property relationships, we compare the basic optoelectronic properties of CuAgBiI5 with those of Cu2AgBiI6 (which has a 2D octahedral network) and reveal a surprisingly low sensitivity to the dimensionality of the octahedral network. The absorption onset of CuAgBiI5 (2.02 eV) barely changes compared with that of Cu2AgBiI6 (2.06 eV) indicating no obvious signs of an increase in charge confinement. Such behavior contrasts with that for lead halide perovskites which show clear confinement effects upon lowering dimensionality of the octahedral network from 3D to 2D. Changes in photoluminescence spectra and lifetimes between the two compounds mostly derive from the difference in extrinsic defect densities rather than intrinsic effects. While both materials show good stability, bulk CuAgBiI5 powder samples are found to be more sensitive to degradation under solar irradiation compared to Cu2AgBiI6.

Manganese Fluoride Nanoparticles Synthesized by Microwave Irradiation Using Ionic Liquid–Ethylene Glycol Mixtures: Room-Temperature Photoluminescence, Crystalline Phase, and Morphology

The facile and rapid microwave-assisted method has been demonstrated to be effective in synthesizing manganese fluoride (MnF2) nanoparticles in binary mixtures of ethylene glycol and imidazolium-based ionic liquid containing fluorine, within a minute, without any surfactant and stabilizer. The effect of volume ratio of an ionic liquid in the binary mixtures with ethylene glycol and the length of the alkyl chain of imidazolium on the morphologies and crystalline structures of MnF2 was investigated. Two types of crystalline phases MnF2, P42/mnm rutile and P4̅2m space group, were synthesized depending on the volume ratio of EMIM BF4. The morphologies of rutile MnF2 clearly varied depending on what kind of ionic liquid was used in the synthesis. MnF2 nanoparticles and spherical nanoclusters assembled by nanospheres were synthesized when the used ionic liquid was OMIM BF4 and EMIM BF4, respectively. Clear room temperature photoluminescence (PL) spectra of MnF2 nanoparticles were observed at ambient pressure. The change of PL spectra depending on the crystalline phase was also observed. In this study, we report that the microwave-assisted method using ethylene glycol–ionic liquid binary mixtures is proper for synthesizing high-quality MnF2 nanoparticles with controllable crystalline phase and morphology.

Two‐Photon Laser‐Written Photoalignment Layers for Patterning Liquid Crystalline Conjugated Polymer Orientation

AbstractSystematic tuning of chemical and physical structure allows fine control over desired electronic and optical properties, including those of conjugated polymer semiconductors. In the case of physical structure, orientation via liquid crystalline alignment allows access to fundamental optical anisotropies and the associated refractive index modification offers great potential for fabrication of photonic structures. In this paper, photoalignment is used to orient the liquid crystalline conjugated polymer poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT), specifically involving two‐photon infrared laser writing of patterns in an azobenzene sulphonic dye (SD1). These patterns are transferred into the overlying film by thermotropic orientation in the nematic melt, then frozen in place by quenching to a room temperature nematic glass. Optimization of laser power and scan speed allows features with linewidths ≤ 1 µm. Photoluminescence (PL) peak anisotropy values reach PLII/PL⊥ = 13 for laser writing, compared with PLII/PL⊥ = 9 for polarized ultraviolet light emitting diode exposure of the same SD1 layer. These two approaches also result in different film microstructures; evidenced by characteristic changes in PL spectra. The anisotropic PL spectra provide information on emissive excited states that complements previous studies on non‐oriented F8BT and related copolymers, also suggesting two emissive states.

Morphology and photoluminescence of nano-porous anodic alumina membranes obtained in oxalic acid at different anodization potentials

Porous Anodic alumina (PAA) with highly ordered pore geometry serves as an ideal template for future development of nanodevices. In the present work, PAA was prepared by varying anodization potential from 10 to 50 V in oxalic acid at 8 °C with a constant electrolyte concentration of 0.3 M. The influence of anodization potential on the structural and photoluminescence (PL) properties of PAA has been studied. The effect of anodization potential on the main pore characteristics of PAA such as pore diameter, interpore distance, pore density, porosity and circularity was studied. It was observed that circularity of PAA was nearly equal to one in the case of anodization potential of 40 V. Highest regularity ratio (RR) obtained for PAA formed in 40 V and it was calculated by WSxM software. It was noticed that with increasing anodization potential there is a slight change in PL spectra of PAA and shows a strong PL peak in blue region.

O2 atmospheric annealing-tunable defects in ionic oxide MgO nanoribbons

An isotropic lattice shrinkage (lattice volume ratio ∼−0.462%) structure was reported in cubic magnesium oxide (MgO) nanocrystals, favoring the enhanced electron correlation. Upon postannealing in an O2 atmosphere, significant changes in photoluminescence spectra were detected in pristine MgO nanoribbons (NRs): a substantial reduction in F+-type centers (Fc) and an increase in a previously unknown peak at 358 nm (3.46 eV) which we attribute to a small polaron (SP) complex as a deep acceptor. A reduced diluted magnetism was found in the O2-annealed MgO NRs. A room temperature electron paramagnetic resonance signal at g ∼ 2.0959 revealed the presence of an unpaired electron trapped in the MgO NRs and a weak broad signal shift at g ∼ 2.0888, suggesting a reduced anisotropic spin–orbit coupling in the O2-annealed MgO NRs. Finally, a view on competition between Fc and SP was proposed: the Fc defect favors FM, and the SP complex leads to reduced FM in MgO NRs. The findings provide new insight into the origin and defect engineering of d0 diluted magnetism in MgO (spin from MgO), and this physical mechanism would be generally applied to other ionic oxide family materials in the field.

Effects of 7.5 MeV electron beam irradiation on optical properties of Eu3+-doped zinc sodium bismuth borate glasses

The present study aims to examine the effects of beaming 7.5 MeV electron on europium-doped zinc sodium bismuth borate glasses (prepared through melt quench technique) and the resulting changes in structural and optical properties. The study also examines the structural depolymerization of irradiated glasses, analyzed using recorded Fourier transform infrared spectra. Absorbance spectra along with Tauc’s plot were used to find the optical band gap of pristine and irradiated glasses. The study observes changes in photoluminescence spectra of irradiated Eu3+-doped glasses, monitored by exciting the samples at 394 nm. The study notes a decrease in emission intensity of Eu3+ ions observed from the emission spectra of electron beam treated glass samples. The thermally stimulated luminescence (TL) measurements of irradiated glasses resulted in intense glow peaks with increasing electron beam doses [4–50 kGy]. The TL glow curve exhibited two dissimilar peaks at distinct temperatures of 490 K and 610 K respectively. The obtained trap-depth (0.93 eV) using Chen’s relation and intensity variation of first glow peak at 490 K as a function electron beam doses facilitates ZNBBE-4 glass for dosimetry applications.

High throughput MOVPE and accelerated growth rate of GaAs for PV application

We present the feasibility of metalorganic vapor phase epitaxy (MOVPE) with extremely high-speed growth of GaAs for solar cell applications. The growth rate was increased up to 120 μm/h, and exhibited an almost linear relationship with the amount of supplied trimethylgallium (TMGa). The thickness variation and doped carrier concentration of GaAs grown at 90 μm/h were comparable to those of conventionally grown GaAs at a lower growth rate. The potential for reducing the V/III supply ratio was investigated to reduce the material cost. Non-doped GaAs wafers were grown at the accelerated growth rate of 90 μm/h, with various V/III ratios. The growth rate of GaAs increased by 20% when the V/III ratio was decreased from 40 to 5. In low temperature photoluminescence (PL) measurement, significant change in PL spectra was not observed, indicating that there was no significant change in quality. The light-power conversion efficiency was almost comparable for V/III ratios from 10 to 40 whereas that at the lowest V/III ratio of 5 was degraded. Photovoltaic (PV) solar cells of GaAs were fabricated with various growth condition. It is found that the performance of the cells grown at 90 μm/h were comparable with previous results.

Integral Method Analysis of Electroabsorption Spectra and Electrophotoluminescence Study of (C4H9NH3)2Pbl4 Organic–Inorganic Quantum Well

Electric-field-induced changes in absorption and photoluminescence (PL) spectra and in PL decay profile have been measured for two-dimensional hybrid organic–inorganic halide perovskite semiconductor, ((C4H9NH3)2Pbl4) (N1). Electroabsorption (E-A) spectra observed at room temperature and at a low temperature of 45 K were analyzed by assuming the Stark shift, and the magnitudes of the change in electric dipole moment and polarizability following photoexcitation were determined. The strong signal observed in the E-A spectra at 45 K was interpreted in terms of the weak absorption band which shows extremely large Stark shift resulting from the large change in polarizability following photoexcitation. Electrophotoluminescence spectra of this compound, that is, field-induced change in PL spectra, show that PL of N1 is quenched by the application of electric field. Field effects on PL decay profiles show that the quenching results both from the field-induced decrease of the population of the emitting state follo...

The dose-dependent photobleaching of CdTe quantum dots in aqueous media

The photobleaching of capped CdTe quantum dots (QDs) possessing a photoluminescence (PL) emission band in green or orange spectral regions (550 nm or 570 nm, respectively) was investigated in aqueous solution under irradiation with violet light. The exposure of QDs had a dose-dependent effect on the photoluminescence intensity revealing three main stages in the variable pattern of its decline. The relatively rapid decrease of PL intensity being observed after the initial doses of exposure was followed by its partial recovery in the dark. The decrease was slower during the middle stage, but become faster again under exposure to the highest cumulative doses. The stages detected in the photoluminescence decrease pattern were also distinguished by monitoring the capacity to recover the reduced PL intensity of QDs and observing the changes in PL spectra as well as absorption spectra. The gradual pattern of the photoluminescence changes is assumed to be a reflection of the photoinduced modification and disintegration of a capping layer of QDs.

Photo-stability study of a solution-processed small molecule solar cell system: correlation between molecular conformation and degradation

Solution-processed organic small molecule solar cells (SMSCs) have achieved efficiency over 11%. However, very few studies have focused on their stability under illumination and the origin of the degradation during the so-called burn-in period. Here, we studied the burn-in period of a solution-processed SMSC using benzodithiophene terthiophene rhodamine:[6,6]-phenyl C71 butyric acid methyl ester (BTR:PC71BM) with increasing solvent vapour annealing time applied to the active layer, controlling the crystallisation of the BTR phase. We find that the burn-in behaviour is strongly correlated to the crystallinity of BTR. To look at the possible degradation mechanisms, we studied the fresh and photo-aged blend films with grazing incidence X-ray diffraction, UV–vis absorbance, Raman spectroscopy and photoluminescence (PL) spectroscopy. Although the crystallinity of BTR affects the performance drop during the burn-in period, the degradation is found not to originate from the crystallinity changes of the BTR phase, but correlates with changes in molecular conformation – rotation of the thiophene side chains, as resolved by Raman spectroscopy which could be correlated to slight photobleaching and changes in PL spectra.

Anisotropic Electric Field Effect on the Photoluminescence of CH3NH3PbI3 Perovskite Sandwiched between Conducting and Insulating Films

Photoluminescence (PL) of a nanocrystalline film of methylammonium lead iodide perovskite (MAPbI3) sandwiched between an electrode of a fluorine-doped tin oxide (FTO) layer and an insulating film of poly(methyl methacrylate) is found to increase and decrease significantly with the application of an external electric field (Fext), depending on the direction of the applied field, based on the measurements of electrophotoluminescence (E-PL) spectra, i.e., field-induced change in PL spectra. The field-induced change in PL intensity is confirmed to originate from the field-induced change in the number of free carriers which induce radiative recombination, based on temporally resolved E-PL measurements. We propose that an internal field (Fint) exists even without application of Fext. The anisotropic behavior of the effect of Fext on PL is interpreted in terms of a synergy effect of Fint and Fext; both fields are additive with the applied field direction from Ag to FTO electrode (positive direction) or subtracti...

Photoluminescence of sulfur-incorporated CIGS solar cells through post-annealing

The photoluminescence (PL) of Cu(In,Ga)Se2 solar cell with sputtered Zn(O,S) buffer layers annealed at various temperatures were measured. As the annealing temperature increased, the peak positions of PL spectra shifted to higher energies. The broad PL spectra were separated two or three emissions, which are suggested to be mostly to donor-acceptor pair transitions with an acceptor due to copper vacancy and donors due to selenium vacancy or IIICu antisite. The changes of PL spectra were discussed from the view of the diffusion of elements, especially sulfur from buffer to absorber during the post-annealing process.

Annealing behaviour of photoluminescence spectra on Cu2ZnSnS4 single crystals

We have measured photoluminescence (PL) spectra at 10 K for Cu2ZnSnS4 (CZTS) single crystals grown by the iodine transport method and explored the anneal changes of PL spectra under a Zn and S‐saturation. All the crystals showed S‐ and Zn‐poor composition, and nearly stoichiometric composition of Cu/(Zn + Sn). The observed PL spectra are divided into two groups; one is PL band with a peak at ∼1.3 eV (1.3‐eV band), and another is PL band with a peak at ∼1.35 eV (1.35‐eV band). It was found from SEM observations that the 1.35‐eV band was observed in crystals with a mirror‐like facet and, on the other hand, the 1.3‐eV band was seen in the crystals with some small dark areas where the composition is Cu‐poor. The Zn‐saturated annealing at 600 °C caused the PL peak shift of ∼0.1 eV, from 1.295 to 1.185 eV. The S‐saturated annealing at 550 °C caused a disappearance of PL emission. The implications of these annealing behaviour are discussed.

Highly improved reliability of amber light emitting diode with Ca -α-SiAlON phosphor in glass formed by gas pressure sintering for automotive applications.

Phosphor in glass (PiG) with 40 wt% of Ca-α-SiAlON phosphor and 60 wt% of Pb-free silicate glass was synthesized and mounted on a high-power blue LED to make an amber LED for automotive applications. Gas pressure sintering was applied after the conventional sintering process was used to achieve fully dense PiG plates. Changes in photoluminescence spectra and color coordination were inspected by varying the thickness of the plates that were mounted after optical polishing and machining. A trade-off between luminous flux and color purity was observed. The commercial feasibility of amber PiG packaged LED, which can satisfy international regulations for automotive components, was successfully demonstrated by examining the practical reliability under 85% humidity at an 85°C condition.

Transformation of Photoluminescence Spectra at the Liposomal Encapsulation of Quantum Dots

Semiconductor quantum dots (QDs) have been extensively used for biomedical applications as efficient biomarkers and biosensors. The liposome encapsulation presents an alternative method for quantum dots labeling to facilitate intracellular delivery of the QDs systems. The semiconductor CdSe/ZnS core/shell quantum dots of two different emission wavelengths (530 and 640nm) were encapsulated in liposomes prepared using a new “chemically green“ method: by sonication and freezingunfreezing procedure and without organic solvents application. The QDs-liposomes hybrids were studied by photoluminescence (PL) spectroscopy before and after quantum dots encapsulation. The liposomes encapsulation of both sizes of quantum dots changes of photoluminescence spectra up to higher emission energies. The advantages of CdSe/ZnS core/shell QDs encapsulation on “green” liposomes may be promising in biomedical applications as efficient biomarkers with water dispersability. At the same time, the energy change of QDs emission due to liposome encapsulation may be interesting for biosensoring applications.