Short-lived Luminescence Research Articles

Isostructural doping for organic persistent mechanoluminescence.

Mechanoluminescence, featuring light emission triggered by mechanical stimuli, holds immense promise for diverse applications. However, most organic Mechanoluminescence materials suffer from short-lived luminescence, limiting their practical applications. Herein, we report isostructural doping as a valuable strategy to address this challenge. By strategically modifying the host matrices with specific functional groups and simultaneously engineering guest molecules with structurally analogous features for isostructural doping, we have successfully achieved diverse multicolor and high-efficiency persistent mechanoluminescence materials with ultralong lifetimes. The underlying persistent mechanoluminescence mechanism and the universality of the isostructural doping strategy are also clearly elucidated and verified. Moreover, stress sensing devices are fabricated to show their promising prospects in high-resolution optical storage, pressure-sensitive displays, and stress monitoring. This work may facilitate the development of highly efficient organic persistent mechanoluminescence materials, expanding the horizons of next-generation smart luminescent technologies.

Luminescence lifetime tuning of non-conjugated organic clusters through external heavy-atom effect for smartphone-based time-resolved imaging

Clusteroluminescence from non-conjugated organic molecules has attracted extensive attention, and it is extraordinarily important to develop effective methods for tuning the clusteroluminescence lifetime with balanced emission intensity in optical multiplexing for time-resolved luminescence imaging. Herein, chitosan, a renewable polymer, was found to exhibit persistent clusteroluminescence after dehydration. In addition, external heavy-atom effect was successfully utilized for enhancing phosphorescence intensity and regulating its phosphorescence lifetime. By adjusting the doping concentration of bromide salts in chitosan, the phosphorescence lifetime could be gradually tailored from 49 to 647 ms. The heavy atoms could promote phosphorescence transition and avoid the reduction of short-lived luminescence component, which facilitated the lifetime-multiplexed information encryption. This strategy for tuning phosphorescence lifetime could be extended to other phosphorescence materials. Moreover, smartphone-based luminescence imaging of shrimp chitin was realized by enhancing its persistent luminescence, which indicated that our method could be used for label-free luminescence imaging of chitin-containing organisms.

Differentiation of black writing ink on paper using luminescence lifetime by time-resolved luminescence spectroscopy

The time-resolved luminescence spectra and the lifetimes of eighteen black writing inks were measured to differentiate pen ink on altered documents. The spectra and lifetimes depended on the samples. About half of the samples only exhibited short-lived luminescence components on the nanosecond time scale. On the other hand, the other samples exhibited short- and long-lived components on the microsecond time scale. The samples could be classified into fifteen groups based on the luminescence spectra and dynamics. Therefore, luminescence lifetime can be used for the differentiation of writing inks, and luminescence lifetime imaging can be applied for the examination of altered documents.

Cathodoluminescence characterization of tridymite and cristobalite: Effects of electron irradiation and sample temperature

Cathodoluminescence (CL) spectra of tridymite and cristobalite have broad peaks around 430 and 400 nm, respectively, both of which can be assigned to the [AlO4/M+]0 defect. The CL intensities of these spectral peaks in the blue region decrease with prolonged exposure to electron irradiation, similar to the short-lived luminescence observed in quartz, although quartz shows a lower decrease in CL intensity compared to these minerals. Cristobalite has a higher CL intensity reduction rate during irradiation than does tridymite. Irradiation of these minerals at low temperatures results in a more rapid decay of CL emission, whereas that of quartz shows no apparent change in the rate of CL emission at similar temperatures. Confocal micro-Raman spectroscopy of the electron irradiated surface of these minerals reveals the amorphization caused by the interaction of the electron beam with the surface layer to a depth of several micrometers. This suggests that such structural destruction diminishes the activity of CL emission centers related to the [AlO4/M+]0 defects by migration of monovalent cations associated with exchanged Al in the tetrahedral sites. Both samples present a considerable reduction of their CL intensities at higher temperature, suggesting a temperature quenching phenomenon. The activation energy in the quenching process was evaluated by a least-squares fitting of the Arrhenius plots, assuming the Mott-Seitz model. The result implies that the energy of non-radiative transition in this process might be transferred to lattice vibrations as phonons in two different manners. This might be related to different irradiation responses of the CL with a change in sample temperature.

Luminescent photoproducts in UV-irradiated ice.

This Account describes the near-UV and visible luminescences emitted from crystalline, polycrystalline, and amorphous ices as a result of excitation by UV light. Vibrationally resolved, short-lived luminescence around 340 nm arises from excited O(2) formed by the reaction of two O atoms. Long-lived luminescence around 420 nm is tentatively assigned to a spin-forbidden (4)sigma(-) --> X(2)Pi transition of OH. This Account gives a history of the research into this little-known phenomenon, places it in the context of other spectroscopic studies of gaseous and solid water, and proposes future directions for the work.

Two-photon excited lifetime imaging of autofluorescence in cells during UVA and NIR photostress.

By monitoring coenzyme autofluorescence modifications, as an indicator of cell damage, the cellular response to femtosecond near-infrared (NIR) radiation (two-photon absorption) was compared with exposure to low-power UVA radiation (one-photon absorption). Excitation radiation from a tunable Ti-sapphire laser, focused through high-numerical-aperture microscope optics, provided diffraction-limited microbeams of an adjustable peak power. Laser scanning NIR microscopy was used to detect spatially the intracellular distribution of fluorescent coenzymes by fluorescence intensity imaging as well as fluorescence lifetime imaging (tau-mapping). Upon the onset of UV or NIR exposure, Chinese hamster ovary cells exhibited blue/green autofluorescence with a mean lifetime of 2.2 ns, which was attributed to NAD(P)H in mitochondria. Exposure to 365 nm radiation from a high-pressure mercury lamp (1 mW, 300 J cm-2) resulted in oxidative stress correlated with increased autofluorescence intensity, onset of nuclear fluorescence, and a fluorescence lifetime decrease. The cellular response to femtosecond NIR microbeams depended significantly on peak power. Peak powers above a threshold value of about 0.5 kW (average power: 6 mW). 0.55 kW (7 mW) and 0.8 kW (10 mW) at 730 nm, 760 nm and 800 nm, respectively, resulted in the onset of short-lived luminescence with higher intensity (100 x) than the intracellular NAD(P)H fluorescence. This luminescence, accompanied by destruction of cellular morphology, was localized and occurred in the mitochondrial region. In contrast, beams at a power of less than 0.5 kW allowed nondestructive fluorophore detection with high spatial and temporal resolution without modification of cellular redox state or cell morphology.

Radiative core-valence transitions in CsMgCl 3 and CsSrCl 3

In this work the spectra and decay times of the intrinsic luminescence of CsMgCl 3 and CsSrCl 3 have been studied. Measurements were undertaken using a pulsed X-ray source (at Saint-Petersburg State Technical University) and SRS at Daresbury Laboratory. The results enable us to relate the short-lived luminescence in the chlorides studied to their radiative core-valence transitions. In addition, the energy band parameters of the crystals were deduced.

Short-lived luminescence of mixed silver halides

Two kinds of excitonic luminescence were investigated for the entire series of solid solutions, AgBr 1− x Cl x , (0 ⪕ x ⪕ 1). The time-resolved spectra observed around 2.5 eV after both pulsed high-power electron beam and N 2-laser irradiations are analyzed in terms of the diffusion-controlled recombination of Frenkel defects Ag 0 i and Ag 2+V - c. It is shown that the effective activation energy of Ag 0 i migration is a linear function of the composition x; and predominantly two kinds of nearest neighbours contribute to this process. The position of maximum of the excitonic molecule luminescence found in mixed monocrystals and fibers reveals a distinctive dependence on the composition x. Its amplitude and half-width correlate with the optical losses in fibers which could be used for their characterization.

Complexation of Eu and Tb with fulvic acids as studied by time-resolved laser-induced fluorescence

Complexation of Eu and Tb with fulvic acids (FA) has been studied by time-resolved laser-induced fluorescence. The lanthanide species are excited by a pulsed Xe/Cl excimer laser and the short-lived luminescence of the fulvic acids is eliminated by time gating. The conditional binding constants ( K′) and the total metal-binding capacities of the fulvic acids have been determined from the equilibrium titration curves. No significant variations of the log K′ values (about 6) have been found in the pH range investigated (2.7, 5.5, 6.5) at ionic strengths of 0.1 and 1 M (NaClO 4). An inverse relationship of K′ to total metal concentration is observed. Substitution of Eu for Al has been found to depress the fluorescence signal of the Eu-FA complex. The binding constants of Al 3+ and Eu 3+, derived from the competition experiments, are of the same order of magnitude. The effect of competition on metal binding and trace-metal transport is discussed.

Perturbation of the phosphorescence decay of propynal upon tea CO2 laser irradiation

The phosphorescence decay of propynal in dilute vapour phase (0.7 torr) is greatly accelerated when subjected to CO2 laser heating. The such perturbed decay can be divided into three periods. The first is characterized by the appearance of a short-lived luminescence ( XXX 20 us), the second by a fast non-exponential phosphorescence decay and the third by a single-exponential decay. In relating the absorbed CO2 laser pulse energy to the induced temperature jump it is shown that the latter decay rate increases exponentially with temperature. Since self-quenching and photodecomposition are not significantly changed upon CO2 laser heating, the temperature dependent triplet decay of propynal is attributed to an intramolecular radiationless decay which becomes increasingly more efficient with rising temperature.

Photochemistry of manganese porphyrins. Part 2.—Photoreduction

Both manganese(II) and (III) porphyrins exhibit low-intensity, short-lived luminescence in ethanol solution at 77 K. Manganese(II) porphyrins are stable towards photodecomposition when irradiated in fluid solution but undergo efficient photoreduction in the presence of a good hydrogen donor such as ascorbic acid. Manganese(III) porphyrins are reduced to the manganese(II) compounds when irradiated with visible light but the quantum yields are very low (≈ 10–4). In water, the quantum yield depends upon pH and excitation wavelength but is independent of the nature of the water-solubilising group. The predominant reaction pathway involves intramolecular reduction via an axially coordinated water molecule. Manganese(IV) porphyrins, which are better described as the manganese(III)π-radical cations, undergo relatively efficient photoreduction in water. Here, reduction leads to formation of hydrogen peroxide and involves attack at the ring periphery rather than at an axial position.