Luminescence Process Research Articles

Upconversion in Nanostructured Materials: From Optical Tuning to Biomedical Applications.

Photon upconversion that is characterized by high-energy photon emission followed by lower-energy excitation has been conventionally studied in bulk materials for several decades. This unique nonlinear luminescence process has become a subject of great attention since 2000 when upconverted emission was demonstrated in nanostructured crystals. In comparison with their bulk counterparts, nanostructured materials provide more room for optical fine-tuning by allowing flexible compositional integration and structural engineering. Moreover, the high colloidal stability of nanoparticles coupled with high amenability to surface functionalization opens up a number of new applications for upconversion, especially in the fields of biology and life science. In this focus review, we discuss recent developments in upconversion materials through nanostructural design and review emerging biomedical applications that involve these nanostructured upconversion materials. We also attempt to highlight challenging problems of these nanomaterials that constrain further progress in utilizing upconversion processes.

Pr3+/Er3+ co-doped tellurite glass with ultra-broadband near-infrared fluorescence emission

Pr3+/Er3+ co-doped tellurite glass with composition 80TeO2-10Na2O-5WO3-5Nb2O5 was synthesized by the conventional melt-quenching technique, and the obtained glass was characterized by the UV/Vis/NIR absorption spectrum, near-infrared fluorescence spectrum, differential scanning calorimeter (DSC) curve, X-Ray diffraction (XRD) pattern and Raman spectrum. Under the 488nm excitation, it was found that Pr3+/Er3+ co-doped tellurite glass could emit an ultra-broadband near-infrared fluorescence which extended from 1200 to 1650nm with full-width at half-maximum (FWHM) of about 236nm, and this ultra-broadband fluorescence was contributed by the multichannel emissions of Pr3+ and 1.53µm band emission of Er3+. The luminescent mechanism and energy transfer processes between Pr3+ and Er3+ ions which are responsible for the observed ultra-broadband fluorescence were analyzed. Meanwhile, optical absorption bands that are assigned with corresponding electronic transitions with respect to Pr3+ and Er3+ ions were identified from the measured absorption spectrum, and based on the optical absorption data, the gain coefficient and important spectroscopic parameters like Judd-Ofelt intensity parameter, spontaneous radiative transition probability, radiative lifetime and branching ratio were calculated to elucidate the radiative properties of doped rare-earth ions. In addition, the DSC curve exhibited the good thermal stability of glass host with ΔT >150°C, Raman spectral study displayed the presence of different vibrational groups and XRD pattern confirmed the amorphous structural nature of the prepared glass. The present results indicate that Pr3+/Er3+ co-doped tellurite glass is promising for the ultra-broadband near-infrared band fiber amplifiers covering the expanded low-loss communication window.

Focus on photonics, spectroscopy, and spectrometry

Femtosecond stimulated Raman spectrometerSection:ChooseTop of pageFemtosecond stimulated Ra... <<Flat-top beam shapersHigh-resolution imaging s...UV lasers for fluorescenc...Neutron imaging system MKS Instruments has launched its Newport femtosecond stimulated Raman spectrometer for scientific research. The nonlinear optical pump–probe instrument combines a narrowband Raman pump, an ultrafast broadband probe, and an ultrafast optical excitation “actinic” pulse. It allows for time-resolved vibrational spectroscopy with simultaneous high spectral and time resolution in the ground and excited states of molecules and yields spectra free from the interference of background fluorescence. Designed to work with amplified femtosecond lasers such as the Spectra-Physics Solstice Ace, the spectrometer can be reconfigured to perform transient absorption spectroscopy and to allow for selected changes such as using an external Raman pump source. MKS Instruments Inc, 2 Tech Dr, Ste 201, Andover, MA 01810, www.mksinst.com Flat-top beam shapersSection:ChooseTop of pageFemtosecond stimulated Ra...Flat-top beam shapers <<High-resolution imaging s...UV lasers for fluorescenc...Neutron imaging system Edmund Optics’ flat-top beam shapers convert collimated Gaussian input beams into collimated flat-top beams with a uniform density distribution and a flat phase front. Featuring an even intensity distribution that is stable over great distances, the converted beam is suitable for microscopy, holography, and system integration. With no internal focusing, flat-top beam shapers are appropriate for applications that require high-power lasers, such as material micromachining. The beam shapers are available with design wavelengths from 266 nm to 10 500 nm for common yttrium aluminum garnet, fiber, and carbon dioxide laser sources. Each operates over a specified wavelength range for laser tuning and can be used with multiple laser sources. Edmund Optics Inc, 101 E Gloucester Pike, Barrington, NJ 08007, www.edmundoptics.com High-resolution imaging spectrographSection:ChooseTop of pageFemtosecond stimulated Ra...Flat-top beam shapersHigh-resolution imaging s... <<UV lasers for fluorescenc...Neutron imaging system Princeton Instruments has added model HRS-500 to its SpectraPro HRS series. The 500 mm focal-length spectrograph and scanning monochromator has an astigmatism-corrected optical system for multichannel fiber applications. The company claims that its spectral deconvolution technology, ResXtreme, optimizes the instrument’s optical performance by improving by as much as 60% the spectral resolution, peak intensities, and consistency across the 2D focal plane. Two exit ports with a full 14 × 30 mm focal plane allow for mounting and operating two array detectors. Applications include Raman spectroscopy, photoluminescence, plasma diagnostics, absorption, and microspectroscopy. Princeton Instruments, 3660 Quakerbridge Rd, Trenton, NJ 08619, www.princetoninstruments.com UV lasers for fluorescence microspectroscopySection:ChooseTop of pageFemtosecond stimulated Ra...Flat-top beam shapersHigh-resolution imaging s...UV lasers for fluorescenc... <<Neutron imaging system Craic Technologies has expanded the capabilities of its 20/30 PV microspectrophotometers by adding deep-UV lasers as excitation sources for them to its laser offerings in the visible to near-IR range. The UV lasers can be used for fluorescence microspectroscopy and can be incorporated into the company’s new photoluminescence package. Both methods require intense light sources, and by exciting in the UV, more materials can be induced to emit photons via a luminescent process. The UV laser output is focused onto a microscopic sample area, and the emitted light is collected and measured by the 20/30 PV microspectrophotometer. The fluorescence or photoluminescence spectra are then analyzed. Craic Technologies Inc, 948 N Amelia Ave, San Dimas, CA 91773, www.microspectra.com Neutron imaging systemSection:ChooseTop of pageFemtosecond stimulated Ra...Flat-top beam shapersHigh-resolution imaging s...UV lasers for fluorescenc...Neutron imaging system << According to Photonis, its Neutronic [i] neutron imaging system provides high resolution and high detection efficiency compared with traditional scintillator-based neutron imaging systems. The system is suitable for physics research, neutron scattering, neutron tomography, and nondestructive testing applications. It uses both cold and thermal neutron imaging techniques to produce still and video images. To achieve neutron sensitivity, Neutronic [i] is equipped with a 100 × 100 mm microchannel plate from Photonis and NeuView technology from Nova Scientific. It houses a vacuum chamber, a high-voltage power supply, and a controller. The system provides short beam-time imaging to protect the items being imaged from damage and can deliver actionable images in under 2 h. Photonis USA Inc, 660 Main St, Sturbridge Business Park, PO Box 1159, Sturbridge, MA 01518, www.photonis.com © 2018 American Institute of Physics.

Bismuth as a versatile cation for luminescence in coordination polymers from BiX3/4,4'-bipy: understanding of photophysics by quantum chemical calculations and structural parallels to lanthanides.

Coordination polymers (CPs) with bismuth(iii) as a connectivity centre have been prepared from BiX3 (X = Cl-I) and 4,4'-bipyridine (bipy) in order to implement Bi-based luminescence. The products were obtained via different synthetic routes such as solution chemistry, melt syntheses or mechanochemical reactions. Five neutral and anionic 1D-CPs are presented that show a chemical parallel to trivalent lanthanides forming isostructural or closely related 1D-CPs, of which five additional compounds are described. Bi3+ proves to be a versatile cation for luminescence resulting from energy transfer processes between a metal and a ligand in the presented CPs. Quantum chemical calculations were carried out to investigate Bi3+-participation in the luminescence processes. The calculated results allow an assignment of the bright transitions composed of mainly metal-to-ligand-charge transfer (MLCT) character. These results show that Bi3+ can form strongly luminescent coordination compounds with N-donor ligands.

Spatially confined luminescence process in tip-modified heterogeneous-structured microrods for high-level anti-counterfeiting.

Recent years have witnessed the progress of lanthanide-doped materials from fundamental material synthesis to targeted practical applications such as optical applications in photodetection, anti-counterfeiting, volumetric display, optical communication, as well as biological imaging. The unique compositions and structures of well-designed lanthanide ion-doped materials could expand and strengthen their application performances. Herein, we report dual-mode luminescent crystalline microrods that spatially confine upconversion and downconversion photophysical process within defined regions using the specially designed heterogeneous structure. Through an epitaxial growth procedure, downconversion tips have been conjugated with the parent upconversion microrods in oriented directions. This spatially confined structure can effectively depress the deleterious energy depletion in lanthanide ions homogeneously doped materials, and as a result, the red, green, and blue upconversion intensities have been enhanced by 334, 225, and 22 times, respectively. Moreover, the induced tips hardly disturb the upconversion process of the microrod seeds. Upon 980 nm laser or ultraviolet lamp excitation, tunable emission colors were realized in the single tip-modified microrod, indicating potential applications of these microrods for high-level dual-mode anti-counterfeiting.

Luminescence of Radachlorin Photosensitizer in Aqueous Solution under Excitation at 405 and 660 nm

Entire luminescence spectrum of a commercial photosensitizer Radachlorin in aqueous solution has been recorded under laser excitation at 660 nm and analyzed. The peak of singlet oxygen phosphorescence at 1274 nm has been observed. The results obtained were compared with those recorded with laser excitation at 405 nm and reported earlier. The comparison showed the similarity of relaxation and luminescence processes occurring in both cases. Effective absorption cross sections were determined at each excitation wavelength, it was also shown that the singlet oxygen quantum yield is independent of photosensitizer concentration. The lifetime of the first excited triplet state in Radachlorin was determined. The results obtained can be used for optimization of the conditions of singlet oxygen generation and detection in solutions and biological samples.

Mutual Effects of Fluorine Dopant and Oxygen Vacancies on Structural and Luminescence Characteristics of F Doped SnO₂ Nanoparticles.

SnO2 and F doped SnO2 (FTO) nanoparticles (NPs) have been synthesized by the hydrothermal method with subsequent annealing at 500 °C. The microstructure and photoluminescence (PL) property of SnO2 and FTO NPs have been investigated, and an assumption model about the luminescence process of FTO NPs has been proposed. All of the SnO2 and FTO NPs possess polycrystalline tetragonal rutile structures, and the average size in the range of 16.5–20.2 nm decreases with the increasing of F doping content. The doping element F is shown a uniformly distribution by electron energy loss spectroscopy (EELS) mapping. The oxygen vacancy concentration becomes higher as is verified by Raman and X-ray photoelectron spectra (XPS). There are three kinds of oxygen chemical states in SnO2 and FTO NPs, in which Oα corresponds to oxygen vacancies. The room temperature PL position is observed to be independent of F doping content. F− may substitute O2− into the SnO2 lattice by generating and one extra e−, which can combine with or to generate or to ensure charge balance.

Effect of Ga content on luminescence and defects formation processes in Gd3(Ga,Al)5O12:Ce single crystals

Luminescence characteristics of Ce3+ - doped Gd3GaxAl5-xO12 single crystals with different Ga contents (x = 1, 2, 3, 4, 5) are studied in the 9–500 K temperature range. The spectra of the afterglow, photoluminescence, radioluminescence, and thermally stimulated luminescence (TSL) of each crystal coincide. The increase of the Ga content results in the high-energy shift of the spectra while the radioluminescence intensity at 9 K remains practically constant up to x = 4. No Ce3+ emission is observed in case of x = 5. The total TSL intensity drastically increases, reaches the maximum value around x = 2–3, and then decreases due to the thermal quenching of the Ce3+ emission. The TSL glow curve maxima are gradually shifting to lower temperatures, and the dependence of the maxima positions and the corresponding trap depths on the Ga content is close to linear. However, the activation energy of the TSL peaks creation under irradiation of the crystals in the 4f – 5d1 absorption band of Ce3+ decreases drastically with the increasing Ga content (especially in the range of x = 1–2), and this dependence is found to be strongly nonlinear. Possible reasons of the nonlinearity are discussed.

Defect induced visible-light-activated near-infrared emissions in Gd3−x−y−zYbxBiyErzGa5O12

Visible-light-activated near-infrared luminescent materials are promising photoluminescent materials due to their convenience and low cost. Crystal defects can seriously affect the performance of luminescent materials, and better understanding of the complexity of the structural disorder and electronic structures of such materials opens up new possibilities in luminescent material development. In this work, we successfully design a novel, effective, visible-light-activated near-infrared luminescent Gd3Ga5O12: 4.2%Yb3+, 8.4%Er3+, and 4.2%Bi3+ system based on first principles. This exhibits strong emission intensity and high luminous efficiency (0.993) and also has a lifetime (7.002 ms) that is at least twice as long as the longest lifetime reported in published papers. We utilize density functional theory with an effective LSDA + U method to study the structural properties of Gd3−x−y−zGa5O12: xYb3+, yBi3+, zEr3+ (GGG: Yb3+, Bi3+, Er3+). The d and f electron orbits of rare-earth ions are considered for an effective Hund exchange. Detailed analysis reveals that GGG: 4.2%Yb3+, 8.4%Er3+, 4.2%Bi3+ has the smallest cell volume because of the strong covalent bonds of Bi–O, Er–O, and Yb–O. Bi 3d is a hybridized state that acts as sensitizing ions during the process of luminescence in GGG: Yb3+, Bi3+, Er3+. Together with experimental and theoretical results, we analyze the influence of defects on emission intensity. The locations of Yb3+, Er3+, and Bi3+ are determined by X-ray absorption fine structure measurements, which are in agreement with the model constructed using first principles. This work may provide innovative guidance for the design of high-performance visible-light-activated near-infrared luminophores based on calculations and a new methodology for application of coherent laser radar and optical communication.

Structural Characterization and Absolute Luminescence Efficiency Evaluation of Gd2O2S High Packing Density Ceramic Screens Doped with Tb3+ and Eu3+ for further Applications in Radiology

Rare earth activators are impurities added in the phosphor material to enhance probability of visible photon emission during the luminescence process. The main activators employed are rare earth trivalent ions such as Ce+3, Tb+3, Pr3+ and Eu+3. In this work, four terbium-activated Gd2O2S (GOS) powder screens with different thicknesses (1049 mg/cm2, 425.41 mg/cm2, 313 mg/cm2 and 187.36 mg/cm2) and one europium-activated GOS powder screen (232.18 mg/cm2) were studied to investigate possible applications for general radiology detectors. Results presented relevant differences in crystallinity between the GOS:Tb doped screens and GOS:Eu screens in respect to the dopant agent present. The AE (Absolute efficiency) was found to rise (i) with the increase of the X-ray tube voltage with the highest peaking at 110kVp and (ii) with the decrease of the thickness among the four GOS:Tb. Comparing similar thickness values, the europium-activated powder screen showed lower AE than the corresponding terbium-activated.

3D Nanostructured Palladium-Functionalized Graphene-Aerogel-Supported Fe3O4 for Enhanced Ru(bpy)32+-Based Electrochemiluminescent Immunosensing of Prostate Specific Antigen.

We developed a novel Ru(bpy)32+-based electrochemiluminescence (ECL) immunosensor utilizing palladium nanoparticle (Pd NP)-functionalized graphene-aerogel-supported Fe3O4 (FGA-Pd) for real-sample analysis of prostate specific antigen (PSA). 3D nanostructured FGA-Pd, as a novel ECL carrier, was prepared by in situ reduction. Large amounts of Ru(bpy)32+ could combine with FGA-Pd via electrostatic interaction to establish a brand-new ECL emitter (Ru@FGA-Pd) for improving ECL efficiency. The obtained Ru@FGA-Pd composite was utilized to label the secondary antibody, which generated strong ECL signals with tripropylamine (TPrA) as a coreactant. Furthermore, we demonstrated that the participation of Pd NPs endowed FGA with favorable electrocatalytic ability in the luminescence process to produce more excited state [Ru(bpy)32+]* for realizing desirable signal amplification. In addition, the primary antibody was captured by gold nanoparticle (Au NP)-functionalized Fe2O3 nanodendrites (Au-FONDs), which possessed good electrical conductivity and favorable biocompatibility. Under optimum conditions, the fabricated sandwich-type ECL immunosensor showed a sensitive response to PSA with a low detection limit of 0.056 pg/mL (S/N = 3) and a calibration range of 0.0001-50 ng/mL. Featuring favorable selectivity, stability, and repeatability, the proposed immunosensor is expected to blaze a novel trail for the real sample detection of PSA and other biomarkers.

Research on the photoluminescence and up-conversion luminescence properties of Y2Mo4O15: Yb, Ho under 454 and 980 nm excitation

Y1.8-xYb0.2HoxMo4O15 (x=0.005, 0.01, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64) phosphors were synthesised at 700°C by using a solid-state reaction method. The samples were characterised by X-ray diffraction, diffuse reflectance spectra, photoluminescence and up-conversion emission spectra. The photoluminescence spectra of Y2Mo4O15:Yb, Ho shows extremely strong green down-shift luminescence corresponding to the 5F4, 5S2→5I8 transition of Ho3+ ions with Ig/Ir>20 under 454nm excitation. While at 980nm excitation, Y2Mo4O15:Yb, Ho sample exhibits unusual red up-conversion luminescence along with a very weak green emission (Ir/Ig=6.4), which is resulted from the severe non-radiative relaxation (5I6→5I7) process due to the very short decay time of 5I6 states of Ho3+ ions. The mechanism of down-shift luminescence is the electrical dipole – dipole transitions. The quenching concentration for down-shift luminescence is higher than that for up-conversion luminescence, which results from the effects of different luminescence processes and large distance between doped rare earth ions in Y2Mo4O15. The different luminescence mechanism and color performance are also studied.

Super broadband near-infrared luminescence in Ni2 +-Er3 + co-doped transparent glass ceramics

Ni2+-Er3+ co-doped glass ceramics containing ZnGa2O4 nanocrystals were fabricated by in situ controlled crystallization method. The adverse energy transfer between Ni2+ and Er3+ could be suppressed in the ZnGa2O4 glass ceramics. And the super-broadband infrared luminescence with full width at half maximum (FWHM) of about 400nm covering 1.1–1.7μm wavelength region was observed in Ni2+-Er3+ co-doped glass ceramics. The two lifetimes of 1NE-GC950 revealed that two luminescence mechanism involved in the luminescence process, Ni2+: 3T2g (3F)→3A2g (3F) and Er3+: 4I13/2→4I15/2 respectively. Compared to that in the Ni2+/Er3+ co-doped glass ceramic containing γ-Ga2O3 and LaF3 nanocrystals, the nanocrystals in the present paper is just only one, ZnGa2O4 nanocrystals, and it could also present super-broadband luminescence.

Optical absorption, luminescence, and energy transfer processes studies for Dy3+/Tb3+-codoped borate glasses for solid-state lighting applications

By using melt quenching technique, good optical quality singly doped Dy3+ or Tb3+ and Dy3+/Tb3+-codoped borate glasses were synthesized and studied by optical absorption, excitation, emission and decay lifetimes curve analysis. Following the absorption spectrum, the evaluated Judd–Ofelt (J–O) intensity parameters (Ωλ (λ = 2, 4 and 6)) were used to calculate the transition probability (AR), the branching ratio (βR), and the radiative lifetime (τR) for different luminescent transitions such as 4I15/2 → 6H15/2, 4F9/2 → 6H15/2, 4F9/2 → 6H13/2, 4F9/2 → 6H11/2 and 4F9/2 → 6H9/2,6F11/2 for the 0.5 mol % singly Dy3+-doped glass. The βR calculated (65%) indicates that for lasing applications, 4F9/2 → 6H13/2 emission transition is highly suitable. For all the Dy3+/Tb3+-codoped glasses, Tb3+: 5D3→7F6 emission decay lifetime curves are found to be non-exponential in nature for different concentrations of Dy3+ codoping. Using the Inokuti-Hirayama model, these nonexponential decay curves were analyzed to identify the nature of the energy transfer (ET) processes and here the electric dipole–dipole interaction is dominant for the ET. Based on the excitation and emission spectra and decay lifetimes curve analysis, the cross relaxation and ET processes between Dy3+ and Tb3+ were confirmed. For the 0.5 mol % Tb3+ and 2.0 mol % Dy3+-codoped glass, the evaluated Tb3+→Dy3+ ET efficiency (η) is found to be 45% under 369 nm excitation. Further, for Tb3+/Dy3+ -codoped glasses, an enhancement of Tb3+ green emission is observed up to 1.5 mol % Dy3+ codoping, and this is due to the non-radiative resonant ET from Dy3+ to Tb3+ upon 395 nm excitation. For singly 0.5 mol % Dy3+ or 0.5 mol % Tb3+-doped glass, the calculated color coordinates (x,y) and correlated color temperatures (CCT) represent the neutral white or warm white light regions, whereas Dy3+/Tb3+-codoped glasses (x,y) and CCT values fall in the yellowish green region with respect to the different Dy3+ concentrations under 350 and 395 nm excitations. Following the analyzed optical data, the singly Dy3+ or Tb3+-doped and Dy3+/Tb3+-codoped glasses could be suggested as promising materials for their applications in solid state light emitting diodes and luminescent display devices.

Luminescence properties of Er3+ doped zirconia thin films and ZrO2/Er2O3 nanolaminates grown by atomic layer deposition

Atomic layer deposited (ALD) ZrO2 (zirconia) thin films doped with Er3+ ions by ion implantation as well as ZrO2/Er2O3 nanolaminates were investigated at wide 5–300 K temperature range using cathodoluminescence (CL) and photoluminescence (PL) spectroscopy under wide range of excitation energies 6–120 eV. In the studied ALD films main emissions due to self-trapped excitons and defect centers were revealed in UV-visible (VIS) region with the excitation bands in the host absorption. In nanolaminates luminescence processes are influenced by their structure and composition. In films with the lower Er3+ ion content, typical 4f luminescence of Er3+ ions were identified being excited through energy transfer from host to doping ions. The luminescence data shows that in contrast to a few hundred nm thick ALD films, the excitonic band near 5.3–5.4 eV are absent in the excitation spectra of nanolaminates with a typical layer thickness of 5 nm, which do not facilitate exciton formation because of limited spatial regularity.

Effects of Gd3+ modifications on the photoelectrochemical properties of TiO2-based dye-sensitized solar cells

In this paper, TiO2 particles (~30 nm) modified with Gd2O3-coating layer (~2 nm) for dye-sensitized solar cells (DSSCs) were fabricated via the hydrothermal method. Among the solar cells based on the Gd3+-doped TiO2 photoanodes, the optimal conversion efficiency was obtained from the 0.025Gd3+-modified TiO2-based cell, with a 17.7% improvement in the efficiency as compared to the unmodified one (7.18%). This enhancement was probably due to the improved UV radiation harvesting via a down-conversion luminescence process by Gd3+ ions, enhancement of visible light absorption and improved dye loading capacity. In addition, after Gd modification, a thin coating could be formed on the TiO2 nanoparticles, which worked as an energy barrier and resulted in a lower charge recombination.

Analysis of TL and OSL kinetics in lithium magnesium phosphate crystals

Within this work the samples of the LiMgPO4 compound have been crystallized using a micro pulling down crystal growth method. The measured TL and OSL response was investigated in order to evaluate basic kinetic parameters. Collected data were analyzed using Tm-Tstop, deconvolution and variable heating rate methods. It was found that both the TL and OSL response of the LiMgPO4 samples can be expressed in the form of a linear combination of several first order components. The obtained results suggest that luminescence processes in the studied material may follow a first order kinetics, as the measured TL glow curves do not shift with increasing dose. Increasing the dose of beta radiation up to kGy range, a linear response was measured for all the studied LiMgPO4 samples. The obtained values of kinetic parameters evaluated with Tm-Tstop method remain in agreement with those obtained by deconvolution for low-temperature peaks. In turn, for peaks located at higher temperatures the results obtained by variable heating rate method are close to those of deconvolution. This implies that more detailed analysis is needed to achieve a compatibility between the applied modes of data analysis and to achieve the accurate values of kinetic parameters. By calculating a decrease in the area under the whole LMP glow curve for the two weeks fading time, using the estimated trapping parameters, and comparing the results with previous work one may conclude that Tm-Tstop method combined with the initial rise analysis gives the most reliable values of kinetic parameters.

Optical, magnetic, and photoelectrochemical properties of electrochemically deposited Eu3+-doped ZnSe thin films

The various mole percent (1–5%) of Eu3+-doped ZnSe thin films were fabricated on the indium-doped tin oxide (ITO) conducting glass substrate by single-step electrochemical deposition (ECD) process in an aqueous medium at 50 °C. The structural, optical, magnetic, and electrochemical properties were characterized as a function of the Eu3+ ion concentration. The X-ray diffraction (XRD) analyses evidenced that the films were hexagonal wurtzite structure along with the (101) preferential orientation. High-resolution scanning electron microscopy (HRSEM) results revealed that the thin films show a spherical like structure for 1–3% of Eu3+-doped ZnSe films. Further, increasing of Eu3+ concentration (4 and 5%), the surface morphology of thin films was observed as agglomerated grain-like structure. The band gap energy of Eu3+-doped ZnSe thin films (2.35 to 2.49 eV) determined by UV-Vis spectra showed a blue shift of absorption edge compared to the pure ZnSe thin film (2.33 eV). The increased band gap by doping of Eu3+ is due to the quantum size effect. The PL emission intensity enhanced by increasing Eu3+ concentration which revealed the enhanced radiative recombination in the luminescence process. The magnetic study revealed that Eu3+-doped ZnSe thin films were ferromagnetic in nature. Electrochemical impedance analysis indicated that 4% of Eu3+-doped ZnSe thin films showed a lower charge transfer resistance (352 Ω) and excellent properties compared to the other samples. Further, the photoelectrochemical measurements carried out for the optimized 4% Eu3+-doped ZnSe thin film revealed the faster migration of photoinduced charge carriers. The present investigation demonstrates that the electrochemically deposited Eu3+-doped ZnSe thin film is a promising candidate for electrochemical device applications.

Photo-transferred thermoluminescence of shallow traps in β-irradiated BeO ceramics

Photo-transferred thermoluminescence signals from beryllium oxide (BeO) ceramics were measured in the low temperature range of 10–300K. Samples irradiated at room temperature using a Sr90/Y90 beta source were cooled down to 10K and trapped charges were photo-transferred at this low temperature using the light from a high power blue LED emitting at ~470nm (2.6eV). Thermoluminescence glow curve recorded at 0.2K/s heating rate exhibited three peaks around 90, 160 and 185K. The analyses of the TL peaks of the glow curve were accomplished using curve fitting, differential and peak shape methods. Results obtained from these techniques are in good agreement about the presence of three trapping centers in BeO ceramics with activation energies of 0.24, 0.48 and 0.56eV. Moreover, the analyses indicated that first-order kinetics (slow retrapping) is the dominant mechanism in the luminescence process. Heating rate dependence of the glow curves was also investigated between 0.2 and 0.8K/s rates.

Dynamics of Charged Excitons and Biexcitons in CsPbBr3 Perovskite Nanocrystals Revealed by Femtosecond Transient-Absorption and Single-Dot Luminescence Spectroscopy

Metal-halide perovskite nanocrystals (NCs) are promising photonic materials for use in solar cells, light-emitting diodes, and lasers. The optoelectronic properties of these devices are determined by the excitons and exciton complexes confined in their NCs. In this study, we determined the relaxation dynamics of charged excitons and biexcitons in CsPbBr3 NCs using femtosecond transient-absorption (TA), time-resolved photoluminescence (PL), and single-dot second-order photon correlation spectroscopy. Decay times of ∼40 and ∼200 ps were obtained from the TA and PL decay curves for biexcitons and charged excitons, respectively, in NCs with an average edge length of 7.7 nm. The existence of charged excitons even under weak photoexcitation was confirmed by the second-order photon correlation measurements. We found that charged excitons play a dominant role in luminescence processes of CsPbBr3 NCs. Combining different spectroscopic techniques enabled us to clarify the dynamical behaviors of excitons, charged excitons, and biexcitons.