Broad Photoluminescence Research Articles

Tunable upconversion emission from oil-based carbon nanodots

Optical properties of carbon dots (CDs), prepared using 10-Undeceonic acid as an organic precursor, exhibited broad range excitation wavelength-dependent photoluminescence, with maximum emission intensity at 3.5 eV. Besides conventional down-conversion PL (DCPL), CDs show excitation wavelength-dependent upconversion PL(UCPL), produced by electromagnetic radiation in the green-NIR wavelength range. The difference between the excitation energy and the UCPL peak energy is found to be constant upon varying the excitation energy, whereas the energy difference with respect to DCPL peak energy decreases linearly. UCPL/DCPL have been explained with the help of surface states, shallow and deep trap states present in the proposed CDs.

Antimony and bismuth cooperation to enhance the broad yellow photoluminescence of zero-dimensional hybrid halide

The incorporation of Sb3+ greatly enhanced the photoluminescence quantum yield of (TMEDA)3Bi2Cl12·H2O from 1% to 38%, the yellow emission originates from the relatively distant highly distorted inorganic octahedra in the structure.

Metallic vs. semiconducting properties of quasi-one-dimensional tantalum selenide van der Waals nanoribbons.

We conducted a tip-enhanced Raman scattering spectroscopy (TERS) and photoluminescence (PL) study of quasi-1D TaSe3-δ nanoribbons exfoliated onto gold substrates. At a selenium deficiency of δ ∼ 0.25 (Se/Ta = 2.75), the nanoribbons exhibit a strong, broad PL peak centered around ∼920 nm (1.35 eV), suggesting their semiconducting behavior. Such nanoribbons revealed a strong TERS response under 785 nm (1.58 eV) laser excitation, allowing for their nanoscale spectroscopic imaging. Nanoribbons with a smaller selenium deficiency (Se/Ta = 2.85, δ ∼ 0.15) did not show any PL or TERS response. The confocal Raman spectra of these samples agree with the previously-reported spectra of metallic TaSe3. The differences in the optical response of the nanoribbons examined in this study suggest that even small variations in Se content can induce changes in electronic band structure, causing samples to exhibit either metallic or semiconducting character. The temperature-dependent electrical measurements of devices fabricated with both types of materials corroborate these observations. The density-functional-theory calculations revealed that substitution of an oxygen atom in a Se vacancy can result in band gap opening and thus enable the transition from a metal to a semiconductor. However, the predicted band gap is substantially smaller than that derived from the PL data. These results indicate that the properties of van der Waals materials can vary significantly depending on stoichiometry, defect types and concentration, and possibly environmental and substrate effects. In view of this finding, local probing of nanoribbon properties with TERS becomes essential to understanding such low-dimensional systems.

Effect of boron doping on luminescent properties of silicon--vacancy and germanium--vacancy color centers in diamond particles obtained by chemical vapor deposition

The effect of doping with boron on the luminescent properties of diamond particles synthesized by Hot Filament Chemical Vapor Deposition technique with color centers embedded during the growth process has been studied. It is shown that at low boron doping level, the photoluminescence intensity of a narrow zero-phonon line of the silicon-vacancy color center (738.2 nm) demonstrates a strong dependence on the concentration of boron atoms at the sites of the diamond lattice. The dependence of the intensity of a broad photoluminescence band in the wavelength range 520-800 nm on the concentration of boron atoms in the gas mixture in the range from 14 to 64000 ppm has been analyzed. The Raman scattering spectra of the obtained particles have been studied. At the concentration of boron atoms in the gas mixture up to 1540 ppm, the Raman scattering spectra of diamond particles practically do not change when the boron concentration is varied. At high boron doping level, the diamond band in the Raman spectra exhibit a spectral response typical of the Fano resonance. Keywords: diamond particles, color centers, boron doping, photoluminescence, chemical vapor deposition.

Optical Properties of Lead-Free Cs-=SUB=-2-=/SUB=-AgInCl-=SUB=-6-=/SUB=- : Bi/SiO-=SUB=-2-=/SUB=- Nanocrystals with Double Perovskite Crystal Structure

The optical characteristics of lead-free nanocrystals with a crystal structure of the double perovskite type with the chemical composition Cs2AgInCl6, doped with bismuth and coated with silicon dioxide were studied, and the possibility of their further application was shown. The optical properties of the nanocrystals under study are analyzed by absorption and luminescence spectroscopy, including those with time resolution. Images were obtained using a scanning electron microscope. The influence of the amount of silicon dioxide precursor addition on the optical properties and morphology of lead-free nanocrystals was established. It is shown that the observed broad photoluminescence band is associated with the occurrence of self-trapped excitons in such nanocrystals. To demonstrate the possibility of practical application of these nanocrystals a light-emitting device based on them was developed and constructed. The light emitting device has a wide emission spectrum close to warm white light. Keywords: LEDs, lead-free perovskites, double perovskites, nanocrystals, photoluminescence.

Systematic study on photoexcited carrier dynamics related to defects in GeSn films with low Sn content at room temperature

Germanium–tin (GeSn) alloys have received much attention thanks to their optical/electrical properties and their operation in the mid-infrared range. However, dislocations/defects in GeSn films serve as trap states, limiting radiative recombination/generation via band-edges. In this work, the impact of the trap states in GeSn with varying Sn contents is investigated. The systematic study reveals that the defects/dislocations in GeSn contribute to the carrier dynamics, mainly originated from the trap states near GeSn/Ge interface. Through photoluminescence (PL) study, the broad PL peak of the trap state for GeSn exists at ∼0.57 eV. The increase in Sn content mitigates the trap-related carrier dynamics. Besides, the increase in GeSn thickness effectively suppresses the interface-related carrier dynamic. By increasing thickness from 180 to ∼900 nm, the external quantum efficiency is enhanced by ∼10×. This study provides a comprehensive understanding of trap-related carrier dynamics in a GeSn material system at room temperature.

Investigation of the optical properties of monocrystalline silicon with a deposited layer of spherical zinc sulfide nanoparticles

In the present work zinc sulfide (ZnS) nanoparticles (NPs) were synthesized on silicon wafer by femtosecond pulsed ablation processing of ZnS bulk target using an electrostatic field in argon gas atmosphere. The morphology, size distribution and structural characterization of obtained ZnS NPs were investigated using scanning electron microscope (SEM), dynamic light scattering (DLS) technique and X-ray diffraction (XRD). Dominant size of obtained NPs lies in the range 10-20 nm, NPs are in spherical shape, particles of other shape and agglomerates of particles are absent. XRD investigation of synthesized NPs identified hexagonal wurtzite structure. There is a structural phase transition from the sphalerite ZnS bulk (target) structure to the structural phase of wurtzite (obtained NPs).The optical characterization of synthesized by laser ablation ZnS NPs was carried out using a photoluminescence (PL) measurement. ZnS NPs show a strong broad PL emission spectra covering the entire visible electromagnetic spectra region (range from 380 to 800 nm) centered at 513.7 nm.

Characterization of tetrahedrite Cu10Cd2Sb4S13 monograin materials grown in molten CdI2 and LiI

Synthesis of Cd-substituted tetrahedrite Cu10Cd2Sb4S13 (THCd) monograin powders are performed by the molten salt synthesis-growth method using two different fluxes: CdI2 and LiI. The X-ray diffraction (XRD) data of the materials indicates that mainly single phase of tetrahedrite Cu10Cd2Sb4S13 compound is formed in both flux salts. XRD pattern of THCd crystals grown in LiI reveals a shift of all diffraction peaks, lower CdS content and a smaller lattice parameter values in comparison with those formed in CdI2. Energy dispersive X-ray spectroscopy reveals stoichiometric composition of Cu10Cd2Sb4S13 crystals grown in CdI2 and Cu-poor grown in LiI. Analysis by Atomic Absorption Spectroscopy confirms the incorporation of Li into THCd crystals at the level of 6.7 × 1020 at/cm3. The photoluminescence (PL) study of Cu10Cd2Sb4S13 microcrystals at T = 10 K shows single broad asymmetric photoluminescence bands with the maxima at around 1.08 and 1.16 eV for materials grown respectively in CdI2 and LiI. The thermal quenching activation energy of this PL band is EA= 88±6 and 199±7 meV for THCd crystals grown in CdI2 and LiI, respectively. Changes in the lattice parameters, composition and shift in PL maximum give evidences of Li incorporation from LiI into the crystal lattice of THCd forming Cu10-xLixCd2Sb4S13 solid solution.

Defects assisted luminescence in m-HfO2 nanocrystals: An experimental and theoretical study

We report here the photoluminescence (PL) and thermoluminescence (TL) of single phase monoclinic (m)-HfO2 nanocrystals. The m-HfO2 shows broad PL in warm white region upon 325 nm excitation, which may be assigned to 4-fold (O4) vacancies as predicted by first principles calculations. TL glow curve of gamma irradiated m-HfO2 comprises of a main peak around 400 K along with a low intensity peak at 480 K, and detailed kinetic analysis confirms the presence of two kinds of metastable traps (0.86 and 1.60 eV). The carrier concentration in shallow traps (0.86 eV) were found relatively much higher than deep traps (1.60 eV), which augurs well for stronger TL signal at 400 K.

Synthesis and photoluminescence of Si-doped boron carbide nanobelts

It is of great interest to synthesize boron carbide nanomaterials and explore their novel properties. We reported the synthesis of belt-like Si-doped boron carbide nanomaterials at a low temperature of 1500 °C with no catalyst. The structures and formation mechanism were investigated. Broad photoluminescence spectra between 400 and 500 nm were observed under 380 nm light excitation. The mechanism of the blue shift of the as-received samples in comparison with the reported boron carbide nanostructured materials is discussed.

Extensive Broadband Near-Infrared Emissions from GexSi1-x Alloys on Micro-Hole Patterned Si(001) Substrates.

Broadband near-infrared (NIR) luminescent materials have been continuously pursued as promising candidates for optoelectronic devices crucial for wide applications in night vision, environment monitoring, biological imaging, etc. Here, graded GexSi1−x (x = 0.1–0.3) alloys are grown on micro-hole patterned Si(001) substrates. Barn-like islands and branch-like nanostructures appear at regions in-between micro-holes and the sidewalls of micro-holes, respectively. The former is driven by the efficient strain relation. The latter is induced by the dislocations originating from defects at sidewalls after etching. An extensive broadband photoluminescence (PL) spectrum is observed in the NIR wavelength range of 1200–2200 nm. Moreover, the integrated intensity of the PL can be enhanced by over six times in comparison with that from the reference sample on a flat substrate. Such an extensively broad and strong PL spectrum is attributed to the coupling between the emissions of GeSi alloys and the guided resonant modes in ordered micro-holes and the strain-enhanced decomposition of alloys during growth on the micro-hole patterned substrate. These results demonstrate that the graded GexSi1−x alloys on micro-hole pattered Si substrates may have great potential for the development of innovative broadband NIR optoelectronic devices, particularly to realize entire systems on a Si chip.

Photoluminescence of Bi3+ doped in YOF phosphor as an activator

Photoluminescence (PL) studies of yttrium oxyfluoride (YOF) doped with bismuth (Bi 3+ ) revealed a broad ultraviolet emission band centered at 31 800 cm −1 that can be applied for silicon solar cells. YOF doped with different Bi 3+ concentrations were synthesized by using the reported pyrolysis technique and annealed at 900 °C. X-ray photoelectron spectroscopy showed two doublet peaks for the Bi 4f region which were attributed to Bi 3+ ions and Bi metal. The PL excitation band was a symmetric broad band centered at 37 500 cm −1 nm and corresponded to the 1 S 0 → 3 P 1 A band with a Stokes shift of 5600 cm −1 . This excitation overlapped with a metal to metal charge transfer band of Bi 3+ . The optimum concentration was 0.4 mol % of Bi 3+ and the quantum yield of this sample was about 60%. • YOF:Bi 3+ revealed a broad UV PL emission band centered at 31 800 cm −1 . • The quantum yield obtained was 60%. • Samples were synthesized by using the pyrolysis technique. • XPS showed Bi 3+ ions and Bi metal.

Radio frequency plasma assisted surface modification of Fe3O4 nanoparticles using polyaniline/polypyrrole for bioimaging and magnetic hyperthermia applications

Surface modification of superparamagnetic Fe3O4 nanoparticles using polymers (polyaniline/polypyrrole) was done by radio frequency (r.f.) plasma polymerization technique and characterized by XRD, TEM, TG/DTA and VSM. Surface-passivated Fe3O4 nanoparticles with polymers were having spherical/rod-shaped structures with superparamagnetic properties. Broad visible photoluminescence emission bands were observed at 445 and 580 nm for polyaniline-coated Fe3O4 and at 488 nm for polypyrrole-coated Fe3O4. These samples exhibit good fluorescence emissions with L929 cellular assay and were non-toxic. Magnetic hyperthermia response of Fe3O4 and polymer (polyaniline/polypyrrole)-coated Fe3O4 was evaluated and all the samples exhibit hyperthermia activity in the range of 42–45 °C. Specific loss power (SLP) values of polyaniline and polypyrrole-coated Fe3O4 nanoparticles (5 and 10 mg/ml) exhibit a controlled heat generation with an increase in the magnetic field.

Tuning the interfacial stoichiometry of InP core and InP/ZnSe core/shell quantum dots

We demonstrate fine-tuning of the atomic composition of InP/ZnSe quantum dots (QDs) at the core/shell interface. Specifically, we control the stoichiometry of both anions (P, As, S, and Se) and cations (In and Zn) at the InP/ZnSe core/shell interface and correlate these changes with the resultant steady-state and time-resolved optical properties of the nanocrystals. The use of reactive trimethylsilyl reagents results in surface-limited reactions that shift the nanocrystal stoichiometry to anion-rich and improve epitaxial growth of the shell layer. In general, anion deposition on the InP QD surface results in a redshift in the absorption, quenching of the excitonic photoluminescence, and a relative increase in the intensity of broad trap-based photoluminescence, consistent with delocalization of the exciton wavefunction and relaxation of exciton confinement. Time-resolved photoluminescence data for the resulting InP/ZnSe QDs show an overall small change in the decay dynamics on the ns timescale, suggesting that the relatively low photoluminescence quantum yields may be attributed to the creation of new thermally activated charge trap states and likely a dark population that is inseparable from the emissive QDs. Cluster-model density functional theory calculations show that the presence of core/shell interface anions gives rise to electronic defects contributing to the redshift in the absorption. These results highlight a general strategy to atomistically tune the interfacial stoichiometry of InP QDs using surface-limited reaction chemistry allowing for precise correlations with the electronic structure and photophysical properties.

Broad photoluminescence in ternary Ag-In-S and quaternary Ag-In-Zn-S nanoparticles: the role of Zn incorporation

Ternary Ag-In-S and quaternary Ag-In-Zn-S nanoparticles with different ratio of Ag/In/Zn/S are synthesized. The incorporation of Zn into Ag-In-S nanoparticles leads to the increase in the optical bandgap and the blue shift of photoluminescence (PL). The optical properties of these nanoparticles are significantly dependent on the chemical composition of nanoparticles. Time-resolved PL spectroscopy in nanosecond time regime is used to study the recombination processes of carriers, which involve the surface states and intrinsic crystallographic defects. These measurements support the donor-acceptor model, in which the PL is achieved by radiative recombination of the localized electron and hole.

Detailed photoluminescence study of Cu2Ge(SSe)3 microcrystals

We present a detailed temperature and laser power dependent photoluminescence (PL) study of Cu2Ge(S0.4Se0.6)3 microcrystals. At T = 20 K, two relatively narrow PL peaks were detected at about 1.16 eV (peak No. 1) and 1.12 eV (peak No. 2) and a weak, broad PL band was detected at about 0.82 eV (peak No. 3). The temperature and laser power dependencies indicate that at T = 20 K, the properties of PL peak Nos. 1 and 2 can be explained by the distant donor–acceptor (DA) pair model where a donor defect has a depth of ED ≈ 20 meV and ED ≈ 60 meV for peak Nos. 1 and 2, respectively. The depth of acceptor defects was 57 and 76 meV for peak Nos. 1 and 2, respectively. At around T = 90 K, the DA pair recombination of peak No. 1 gradually starts to transform into the conduction band–acceptor recombination, but peak No. 2 shows a DA pair recombination even at room temperature. The estimated bandgap energy of this compound at room temperature was Eg = 1.225 eV.

Quantum dot assisted luminescent hexarhenium cluster dye for a transparent luminescent solar concentrator

A luminescent solar concentrator (LSC) is a solar-light harvesting device that concentrates light on a photovoltaic cell placed at the edge of an LSC panel to convert it into electricity. The nano-sized inorganic–organic cluster complex (dMDAEMA)4[Re6S8(NCS)6] (this refers to RMC where dMDAEMA is 2-dimethyl amino ethyl methacrylate) is a promising candidate for LSC luminophores due to its downshifted broad photoluminescence suitable for photovoltaic cells. However, the low quantum yield (QY) of RMC limits the performance. Here, zinc-doped CuGaS/ZnS core/shell quantum dots (ZQD) were used as energy transferring donor with high QY to improve the performance of the LSC. The two metal chalcogenide luminophores, RMC and ZQD, are chemically suitable for dispersion in an amphiphilic polymer matrix, producing a transparent waveguide with suppressed reabsorption and extended harvesting coverage of the solar spectrum. We achieved an ηopt of 3.47% and a PCE of 1.23% while maintaining greater than 80% transparency in the visible range. The high performance of this dual-dye LSC with suppressed reabsorption, and scattering losses is not only due to uniform dispersion of dyes in a polymer matrix, but also energy transfer from ZQD to RMC. This report suggests a new possibility for promising various multi-dye LSCs for use in building-integrated photovoltaic windows.

Synthesis and characterization of CeF3‒doped (74.5-x)P2O5:20Li2O:5Al2O3:x(GdF3, LaF3 and YF3) glasses

Glasses have a wide variety of applications in different types of devices, including solid-state lasers, fiber-optic amplifiers, medical imaging, radiation dosimeter, solar cells, neutron imaging, and scintillators. Among several rare-earth (RE) ions, Ce3+ exhibits short decay time and offers promising scintillation when it is doped in a transparent glass matrix. The objective of this study was to investigate the energy transfer from Gd3+, La3+, and Y3+ ions to Ce3+ ion in 64.5P2O5:20Li2O:5Al2O3 glass matrix while considering an enhancement in its scintillation efficiency. Four glass samples doped with CeF3 alone and co-doped with GdF3, LaF3, and YF3 were fabricated. Broad photoluminescence and radio-luminescence emissions peaking near to 340 and 350 nm were found when excited by 310 nm and X-ray, respectively, for all the glasses. A photoluminescence emission quenching was found in LaF3 co-doped glass. A strong energy transfer from Gd3+ to Ce3+ was noticed while the GdF3 co-doped glass was excited by X-ray, 275 nm (from Gd3+), and 310 nm (from Ce3+) excitations. The Gd3+ co-doped glass consisted of a 37 ns decay constant under the 266 nm laser excitation. The thermoluminescence analysis showed two glow curves centered at 210 °C and 345 °C, respectively, after X-ray irradiation. Considering the efficient energy transfer from Gd3+ to Ce3+ ions and short lifetime of Ce3+ emission, the glass composition of the above formula having Gd3+ and Li+ with Ce3+ ions appeared to be a promising candidate in the search of good promising scintillating glasses with fast fluorescence decay time.

Link between Structural and Optical Properties of CoxFe3–xO4 Nanoparticles and Thin Films with Different Co/Fe Ratios

CoxFe3–xO4 nanoparticles (x = 0.4 to x = 2.5) and thin films (x = 0.9 to x = 2.2) are analyzed by Raman, absorption, and photoluminescence spectroscopy to link structural and optical properties to different cobalt to iron (Co/Fe) ratios. Raman spectroscopy shows that with decreasing Co content, the crystal structure changes from a predominantly normal cubic spinel phase to a mixed inverse spinel phase. This finding is supported by absorption spectroscopy that points out that inter valence charge transfer (IVCT) processes between octahedrally coordinated Co2+ and Fe3+ cations become more prominent with increasing Fe content. Independent of the Co/Fe ratio, CoxFe3–xO4 nanoparticles show a broad photoluminescence (PL) band with a maximum at around 510 nm. Time-resolved photoluminescence spectroscopy shows subnanosecond lifetimes and temperature-resolved photoluminescence experiments reveal that the green PL increases with decreasing temperature (300 to 10 K) while showing no temperature-dependent shift in energy. It is proposed that this green PL originates from OH-groups on the particles’ surface.

MgAl2O4:Cr3+ luminescence thermometry probe in the physiological temperatures range

Temperature sensing from the photoluminescence of MgAl2O4:Cr3+ ceramic powder is systematically investigated. Material was prepared by self-propagating high temperature synthesis method. In this host, Cr3+ experiences the strong crystal field, so the overlapping emissions from 2E and 4T2 energy levels are observed. Emission and excitation spectra were recorded from 300 K to 540 K. The broad photoluminescence attributed to 4T2→4A2 emission gains in intensity with increase in temperature on account of 2E→4A2 emission intensity until 460 K when both emissions start quenching. The emissions were separated by deconvolution at each temperature and used for the luminescence intensity ratio temperature readout method. The obtained relative sensitivity exhibited high values in the physiological range, from 3.5 %K−1 at 300 K to 2.9 %K−1 at 330 K, above 2 %K−1 below 400 K and above 1 %K−1 between 400 K and 540 K.