Emission Decay Research Articles

Resolving conjugated polymer film morphology with polarised transmission and time-resolved emission microscopy

The alignment of chromophores plays a crucial role in determining the optoelectronic properties of materials. Such alignment can make interpretation of fluorescence anisotropy microscopy (FAM) images somewhat ambiguous. The time-resolved emission behaviour can also influence the fluorescence anisotropy. This is particularly the case when probing excitation energy migration between chromophores in a condensed phase. Ideally information concerning the chromophoric alignment, emission decay kinetics and fluorescence anisotropy can be recorded and correlated. We report on the use of polarised transmission imaging (PTI) coupled with both steady-state and time-resolved FAM to enable accurate identification of chromophoric alignment and morphology in thin films of a conjugated polydiarylfluorene. We show that the combination of these three imaging modes presents a comprehensive methodology for investigating the alignment and morphology of chromophores in thin films, particularly for accurately mapping the distribution of amorphous and crystalline phases within the thin films, offering valuable insights for the design and optimization of materials with enhanced optoelectronic performance.

Separated Electronic and Strain Interfaces in Core/Dual‐Shell Nanowires: Unlocking the Potential of Strained GaAs for Applications Across Near‐Infrared

AbstractSemiconductor nanowires have inspired plenty of novel nanotechnology device concepts in photonics, electronics, and sensing, owing to their unique functionalities and integrability in heterogeneous platforms. Lattice‐mismatched core/shell heterostructures, in particular, open new avenues for strain engineering and material properties modification. A notable case is the widely tunable tensile strain in the core of GaAs/InxAl1‐xAs core/shell nanowires, which can be used to tailor the GaAs bandgap for applications across near‐infrared, like optical fiber telecommunication, imaging, photovoltaics, etc. As it is shown here, though, the bandgap narrowing under high tensile strain in the GaAs core is accompanied by fast non‐radiative recombination, which is undesirable for any device application. The limiting role of the lattice‐mismatched core/shell interface is revealed, and a novel core/dual‐shell heterostructure that employs an intermediate AlyGa1‐yAs shell (spacer) is proposed. This spacer decouples the GaAs/AlyGa1‐yAs interface, which confines electrons and holes into GaAs, from the lattice‐mismatched AlyGa1‐yAs/InxAl1‐xAs one, whereas the strain in GaAs is unaffected. Choosing the optimal spacer thickness, the photoluminescence yield increases significantly, with longer emission decay lifetimes and slower carrier cooling rates. Besides unlocking the potential of GaAs for photonic applications across near‐infrared, the proposed heterostructure concept can also be adopted for other material systems.

Visible and NIR steady-state luminescence properties of Dy3+ ions-doped calcium phosphate glasses for light-emitting diodes

In this paper, we systematically investigate photoluminescence attributes of dysprosium (Dy3+) ions-doped calcium phosphate, (99-x) P2O5 + x CaO + 1.0 Dy2O3 (x = 20, 30 and 40) (CaPDy) glass samples fabricated via the melt-quenching method. The luminescence emission spectra unveiled the visible emission at 484 nm and 573 nm and near-infrared emission at 1011 nm under the excitation wavelength of 349 nm. The emission decay kinetic studies reveal that the decay profiles exhibit non-exponential behaviour. Furthermore, the CIE chromaticity coordinates, and the ratio of Y/B using 573 nm 484 nm emission intensities were evaluated and further utilized to estimate the CCT values. The results show that the studied glass samples has potential for the yellowish cool light applications.

Spectroscopic and electrical properties of europium doped bismuth antimony fluoroborate glasses

Strong luminescence in the red spectral region is a well-known characteristic of the trivalent europium ion (Eu3+). We investigate a novel europium doped glassy substance for their use in optical devices, optoelectronics and radiation shielding. By using the traditional melt quenching technique, Bismuth antimony fluoroborate glasses are synthesized. XRD investigations support the amorphous nature of the material. Spectral measurements of absorption, photoluminescence (PL) excitation, PL emission, and PL decay curve are made in order to study the lasing properties. Judd-Ofelt (J-O) intensity parameters, from emission spectra, exhibit the trend Ω2> Ω4 furthermore used to find the radiative parameters-transition probability (AR), branching ratio (βR), radiative lifetime (τR), and stimulated emission cross-section (σse) for all the glasses. Decay curves show single exponential behavior and is used to find the quantum efficiency of the prepared glasses. The dielectric properties (dielectric constant (ɛ′), dielectric loss (ɛ″)), impedance and electrical conductivity (σac) of these glasses with variation in frequency have also been studied at the ambient temperature. The radiation shielding properties are evaluated for the photon energy range (1 keV–15 MeV). Based on the trends noticed in the radiative parameters, electrical conductivities and radiation shielding parameters, the present glasses could be found useful as optoelectronic devices, non-linear optical materials, battery anode materials and radiation shielding purposes.

B¯0→K¯(*)0X , B−→K(*)−X , B¯s0→η(η′, ϕ)X from the X(3872) molecular perspective

We study the decays B¯0→K¯0X, B−→K−X, B¯s0→η(η′)X, B¯0→K¯*0X, B−→K*−X, B¯s0→ϕX, with X≡X(3872), from the perspective of the X(3872) being a molecular state made from the interaction of the D*+D−,D*0D¯0, and c.c. components. We consider both the external and internal emission decay mechanisms and find an explanation for the K¯0X and K−X production rates, based on the mass difference of the charged and neutral D*D¯ components. We also find that the internal and external emission mechanisms add constructively in the B¯0→K¯0X, B−→K−X reactions, while they add destructively in the case of B¯0→K¯*0X, B−→K*−X reactions. This feature explains the decay widths of the present measurements and allows us to make predictions for the unmeasured modes of B¯s0→η(η′)X(3872) and B−→K*−X(3872). The future measurement of these decay modes will help us get a better perspective on the nature of the X(3872) and the mechanisms present in production reactions of that state. Published by the American Physical Society 2024

Concentration and temperature dependence of Pr3+ f-f emissions in La(PO3)3

La(PO3)3 activated with different concentrations of Pr3+ was synthesized by a solid-state process. The obtained powder was composed of chunks of several microns in size, typical for this type of synthesis. X-ray diffraction confirmed an orthorhombic crystal structure with the C2221 space group. The electronic band structures and density of states of La(PO3)3 and La(PO3)3:Pr3+ are calculated and presented. The visible and near-infrared emissions from Pr3+ [Xe]4f2→ [Xe]4f2 electronic transitions were detected under 442 nm excitation. The red emission from the 1D2 state dominates visible spectra while emissions from the 3P0,1,2 states have smaller intensities. The 1D2 emission centered around 1020 nm is detected in the near-infrared spectral range. Intensities of 3P0 emissions increased with an increase in Pr concentration, while 1D2 emissions decreased in intensity. We found that the main process responsible for the 1D2 state decay is the Pr(1D2) + Pr(3H4) → Pr(1G4) + Pr(3F3,4) cross-relaxation between two Pr ions of electric dipole-dipole character. This finding is supported by 1D2 emission decay measurements, which revealed a reduction of average decay constants from 242 μs for a 0.5 mol% doped sample to 11 μs for a 10 mol% doped sample and an increasingly stronger non-exponential behavior of emission decay patterns with an increase in Pr3+ concentration.

Behavior analyses of chromium into LiZnNbO4 host through optical spectroscopy and X-ray diffraction

A LiZnNbO4 sample was produced through the solid-state reaction method, according to which, chromium was introduced in the sample as impurity. X-ray diffraction (XRD), luminescence, excitation, emission decay time and emission quantum efficiency analyses were carried out. Structural analysis based on the sample's XRD data showed LiZnNbO4 compound belonging to the P4122 space group. Luminescence measurements evidenced broad emission band centered at 800 nm, which was associated with spin-allowed electronic transition from the excited state 4T2(4F) to the fundamental state 4A2(4F). Emission decay time reached 7.8 μs under 460 nm excitation and 0.43 quantum efficiency. Excitation spectrum showed bands associated with of Cr3+ ions transitions4A2(4F)→ 4T1(4F) and 4A2(4F)→ 4T2(4F), at 460 nm and 644 nm, respectively in octahedral symmetry. Crystal field parameter Dq = 1553 cm−1 and Racah B = 621 cm−1 were found by using transition energies from both the excitation spectrum and Tanabe-Sugano matrices.

Effect of pH on Ellagic acid and its complexation with gamma-cyclodextrins

In food chemistry, the determination of the Ellagic acid (EA) from a food sample by Cyclodextrins (CDs) based nanosensor is a cheap, rapid, and sensitive method. EA acts as a ligand of CDs encapsulation. This study describes the effect of pH on EA and EA-γ-CD complex formation with the aid of spectroscopic and emission decay measurement. From this study, it was observed that pH of the medium has a high effect on the photophysical properties of EA and EA-γ-CD complexes. Due to larger cavity size, γ-CD forms a 1:1 stoichiometric complex with EA. Based on our results, it can be concluded that the stability of the complex between EA and γ-CD enhanced in an acidic medium. From the binding energy calculation by DFT method, it was observed that the encapsulation of EA in the cavity of γ-CD from the front side is more favorable compared to the back side to form EA-γ-CD complex. Such investigation should provide new information that will make it possible to improve the quality and safety of food. This study will be helpful in the use of γ-CD as a biosensor for EA determination.

Upper limits of 44Ti decay emission in four nearby thermonuclear supernova remnants

ABSTRACT To identify progenitors and investigate evidence of He burning, we searched for decay radiation of freshly synthesized 44Ti in four young nearby thermonuclear supernova remnants: Kepler, SN 1885, G1.9+0.3, and SN 1006, by analysing the up-to-date NuSTAR archival data. No apparent flux excess from the 68 and 78 keV line emissions accompanying decay was detected above the power-law continuum applied for the remnants and the absorbed stray light. By comparing the inferred upper limits of the line flux and the initial 44Ti masses with a wide variety of supernova nucleosynthesis models, we placed constraints on the supernova progenitors. We derived the first NuSTAR line flux upper limit for Kepler and ruled out most of the double-detonation scenarios with a thick He layer under low density. We estimated, for the first time, the upper limit for SN 1885, which is high because of the large distance, yet still remains consistent with the He shell detonation. The new flux and mass limit of G1.9+0.3 derived from a longer total exposure is lower than the results from previous studies and evidently excludes explosive burning of He-rich matter. The relatively advanced age and the large spatial extent of SN 1006 have prevented meaningful constraints.

Giant Quantum Electrodynamic Effects on Single SiV Color Centers in Nanosized Diamonds.

Understanding and mastering quantum electrodynamics phenomena is essential to the development of quantum nanophotonics applications. While tailoring of the local vacuum field has been widely used to tune the luminescence rate and directionality of a quantum emitter, its impact on their transition energies is barely investigated and exploited. Fluorescent defects in nanosized diamonds constitute an attractive nanophotonic platform to investigate the Lamb shift of an emitter embedded in a dielectric nanostructure with high refractive index. Using spectral and time-resolved optical spectroscopy of single SiV defects, we unveil blue shifts (up to 80 meV) of their emission lines, which are interpreted from model calculations as giant Lamb shifts. Moreover, evidence for a positive correlation between their fluorescence decay rates and emission line widths is observed, as a signature of modifications not only of the photonic local density of states but also of the phononic one, as the nanodiamond size is decreased. Correlative light-electron microscopy of single SiVs and their host nanodiamonds further supports these findings. These results make nanodiamond-SiVs promising as optically driven spin qubits and quantum light sources tunable through nanoscale tailoring of vacuum-field fluctuations.

The decay curves of luminescence from Eu2+ in β-SiAlON are effectively analyzed using the general-order kinetics formula

Defects in phosphors affect not only luminescence intensity but also emission peak width, decay time, and afterglow. The green phosphor β-SiAlON:Eu2+ exhibits the green emission of Eu2+ at 520 nm and the blue emission of nitrogen vacancies at 460 nm in time-resolved fluorescence measurements. The decay time of the intrinsic Eu2+ transition is 0.7 μs, but afterglow is detected from 50 μs to 0.01 s. This afterglow decay curve is the same for the green emission of Eu2+ and the blue emission of nitrogen vacancies, suggesting that the defect levels of the nitrogen vacancies affect the Eu2+ transition. The afterglow decay curves were analyzed using the formula of the general-order kinetics, 1+t/τB−n , where n is the decay power and τB is the decay time. This equation is generally used when analyzing afterglow on the order of seconds to hours but has not been examined systematically applied in samples with different concentrations of Eu2+ and temperatures on the order of nanoseconds to milliseconds. The decay power n is approximately 1 for all Eu2+ concentrations (x = 0.001–0.3) and undoped β-SiAlON. The decay time τB is correlated with the density of the nitrogen vacancies determined by electron spin resonance. Furthermore, the value of n is approximately 1 for 50 μs to 0.01 s and 0.3 for 1–1000 s. Thus, the luminescence mechanism of Eu2+ can be discussed by comparing n and τB obtained from the decay curves. In addition, several different Eu2+-doped phosphors, namely SrAl2O4:Eu2+, Dy3+, CaAlSiN3:Eu2+, and CaS:Eu2+, Tm3+, are studied.

Acceleration of emission decay in Ce-doped Gd-containing garnets by aliovalent codoping due to blocking excitation transfer via gadolinium subsystem

Substantially faster scintillators for radiation detectors are currently in demand for future high-luminosity high energy physics experiments and medical imaging devices. To meet this demand, the excitation transfer through Gd-sublattice in Ce-activated garnet-type scintillators is studied by time-resolved cathodoluminescence (CL) and photoluminescence (PL) techniques. The transfer is evidenced in the different decay rate in CL experiments and after resonant photoexcitation of Ce ions and is confirmed by the simulation of excitation transport through gadolinium subsystem and from Gd3+ to Ce3+ ions using the Monte Carlo technique. Energy levels of Gd3+ involved in the transfer are identified. The comparison of the results of time-resolved PL and CL measurements and the simulations of carrier dynamics revealed that the emission decay in Ce-doped Gd-containing garnets is accelerated by aliovalent codoping due to blocking the excitation transfer via gadolinium subsystem.

Dual-mode optical thermometry and multilevel anti-counterfeiting based on Er3+/Eu3+ doped Ba5Gd8Zn4O21 phosphors

Designing and manufacturing novel anti-counterfeiting materials with multilevel, strong readability and inexpensive is a crucial challenge. Herein, a batch of Ba5Gd8(1-x-y)Zn4O21:xEu3+/yEr3+ phosphors with long persistent and multicolor luminescence were synthesized. Their structure and luminescence properties were studied through X-ray diffraction, scanning electron microscope, lifetime decay curves, emission, excitation, thermoluminescence and diffuse reflection spectra. Under different wavelengths irradiation, Ba5Gd8Zn4O21:Eu3+, Ba5Gd8Zn4O21:Er3+ and Ba5Gd8Zn4O21:Eu3+, Er3+ emit strong red, green and multicolor (green, yellow, red) luminescence, respectively. Importantly, Ba5Gd8Zn4O21:Eu3+ and Ba5Gd8Zn4O21:Eu3+, Er3+ phosphors exhibit long-lasting luminescence after 254 nm and X-ray radiation. Combine long afterglow and multicolor emissions under X-ray, UV and 980 nm laser excitation, these materials successfully achieve multilevel anti-counterfeiting. In terms of optical temperature measurement, the maximum relative sensitivity of Ba5Gd7.44Zn4O21:0.07Er3+ based on thermal coupling levels (2H11/2/4S3/2) and non-thermal coupling levels (4F9/2/2H11/2) of Er3+ are 1.29 % K−1 and 0.34 % K−1, respectively. Both two modes exhibit superior repeatability (98 %) in 333–573 K temperature range which can realize self-calibration temperature sensing. All findings reveal great potential of these phosphors for multilevel anti-counterfeiting and efficient optical temperature sensing.

Classical Purcell factors and spontaneous emission decay rates in a linear gain medium

Classical Purcell factors and spontaneous emission decay rates in a linear gain medium

Reductive quenching of photosensitizer [Ru(bpy)3]2+ reveals the inhomogeneous distribution of sites in PAN polymer nanofibers for light-driven redox catalysis.

Integration of molecular photocatalysts into redox-inert polymers constitutes a path towards photocatalytically active, lightweight materials. In particular, electrospun polymer fibers hold potential due to their favorable surface-to-volume ratio and their straightforward fabrication. This study focuses on the polyacrylonitrile (PAN) fibers, into which the prototype photosensitizer (PS) ruthenium tris(bipyridine) [Ru(bpy)3]2+, has been embedded by electrospinning. Studying the interaction between the optically excited [Ru(bpy)3]2+ with a non-redox inert solvent within the nanofibers, we resolve a distribution of microenvironments, which differ by the extent to which the photosensitizer is exposed to the solvent. This results in a non-exponential decay of the complex's emission and pronounced differences in the transient absorption signals.

Broadband near-infrared luminescence in a cubic pyrophosphate Al0.5Ta0.5P2O7:Cr3+ phosphor for multi-functional applications.

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are considered as next-generation of NIR light sources for spectroscopy. However, it is still a challenge to develop an inexpensive broadband NIR phosphor with relatively long-wavelength (λem > 800 nm) emission. In this work, an octahedral Al3+-containing pyrophosphate Al0.5Ta0.5P2O7 with a cubic structure was chosen as a host for Cr3+. Synthesizing this material indicates that this phosphor exhibits a broadband NIR emission peaking at 850 nm with a full width at half maximum (FWHM) of 155 nm under 465 nm excitation. The crystal structure, morphology, local structure, and photoluminescence properties of this material were investigated in detail. The results revealed a full understanding of this new material. A NIR pc-LED device fabricated by using this material combined with a 450 nm LED chip generates a NIR output power of 10.7 mW and a NIR photoelectric conversion efficiency of 3.4% under a 100 mA driving current, which shows the possibility of this material to be utilized in NIR pc-LED applications. Moreover, this material exhibits a linear relationship between emission intensity, decay time and temperature in a wide temperature range, implying that excellent multi-model temperature sensing applications can be expected.

Multiphoton emission of single CdZnSe/ZnS quantum dots coupled with plasmonic Au nanoparticles.

The fluorescence blinking and low multiphoton emission of quantum dots (QDs) have limited their application in lasing, light-emitting diodes, and so on. Coupling of single QDs to plasmonic nanostructures is an effective approach to control the photon properties. Here plasmon-exciton systems including Au nanoparticles and CdZnSe/ZnS QDs were investigated at the single particle level. With the modulation of the local electromagnetic field, the fluorescence intensity of single QDs is increased, accompanied by a significant suppression in blinking behavior, and the lifetime is shortened from 15 ns to 2 ns. Moreover, the second-order photon intensity correlation at zero lag time g2(0) of coupled single QDs is larger than 0.5, indicating an increased probability of multiphoton emission. The enhancement factors of radiative and nonradiative decay rates of QDs coupled with Au nanoparticles are calculated. The sharply increased radiative decay rate can be comparable to the nonradiative Auger rate, leading to dominated multiple exciton radiative recombination with PL intensity enhancement, suppressed blinking, lifetime shortening, and multiphoton emission. The results of the exciton decay dynamics and emission properties of single QDs in this work are helpful in exploring the mechanism of plasmon-exciton interaction and optoelectronic application of single QDs.

Non-equivalent Mn4+ doping in mixed-anion host of K3Na(MoO2F4)2·H2O achieving short fluorescence lifetime and intense zero phonon line

The parity-selection rule for the Mn4+ d → d intra-configurational transition becomes relaxed after placing it into Mo6+-based distorted octahedra, which induced an oxyfluoride phosphor with fast decay and intense zero phonon line emission.

Effect of the bulkiness of alkyl ligands on the excited-state dynamics of ZnO nanocrystals.

Organic ligands on the surface of nanocrystals (NCs) are extremely important in influencing various physical properties, such as dispersibility, electrical properties, and optical properties. Recent studies have revealed that a slight difference in the molecular structure of aliphatic organic ligands significantly affects the dispersibility of the NCs. On the other hand, the effects of the difference in the molecular structure of ligands on the excited-state dynamics of NCs remain elusive. In this study, we synthesized a series of colloidal ZnO NCs capped with different alkyl phosphonic acids and investigated their photophysical properties using emission decay measurements and transient absorption spectroscopy. The spectral shape and lifetime of the emission originating from the surface oxygen defects of ZnO NCs are almost the same irrespective of the alkyl phosphonic ligands used, indicating that the electronic states of the surface oxygen defects are not affected by the bulkiness of the ligand. On the other hand, the emission quantum yield correlates with the rate of carrier trapping by oxygen defects, suggesting that the rate of carrier trapping reflects the number of oxygen defects. Revealing the detailed relationship between molecular structures of organic ligands and the optical properties of NCs is important for advanced photofunctional superstructures using semiconductor NCs.

Simultaneously enhancing organic phosphorescence quantum yields and lifetimes for triphenylphosphine salt doped polymer films.

Simultaneously enhancing the quantum yields and luminescence lifetimes of organic persistent room temperature phosphorescence (RTP) molecules is a priority in the organic photonic area, but it remains a formidable challenge. Here, an effective strategy was proposed to improve both quantum efficiencies and emission decay times for phosphorescent triphenylphosphine salts. This approach involves integrating an electron donor unit into a triphenylphosphine salt via an alkyl chain. This structure facilitates an intermediate through-space charge transfer excited state, which enhances the intersystem crossing process to boost RTP performance. Moreover, the electron donor moiety contributes additional triplet excitons to the triphenylphosphine salts through triplet-to-triplet energy transfer, substantially increasing the population of triplet excitons. Specifically, compared to butyl(naphthalen-1-yl) diphenylphosphonium bromide (Φphos. = 4.9% and τ = 255.79 ms), (2-(9H-carbazol-9-yl)ethyl)(naphthalen-1-yl)diphenylphosphonium bromide demonstrates a higher phosphorescence quantum yield of 19.6% and an extended emission lifetime of 800.59 ms. This advancement lays the groundwork for developing high-performance organic RTP materials, unlocking new possibilities for advanced photonic applications.