Slow Luminescence Research Articles

Slow magnetic relaxation and luminescence properties in β-diketonate lanthanide(iii) complexes. Preparation of Eu(iii) and Yb(iii) OLED devices

Six β-diketonate compounds [Ln(btfa)3(4,4′-dinonylbipy)] Ln = Sm, Eu, Tb, Dy, Er and Yb are reported. Magnetic and Luminescence study is also filed. The Eu and Yb complexes were successfully used as emitters in multilayer vacuum-deposited OLEDs.

Ultrafast Decay, Ultrahigh Spatial Resolution, and Stable γ-CuI Single Crystal Treated by Iodine Annealing and SiO2 Coating.

The demand for scintillators with ultrafast decay times, high spatial resolutions, and high stabilities is increasing due to the development of ultrafast hard X-ray detection, hard X-ray imaging, and high-energy physics facilities. γ-CuI single crystals, which exhibit ultrafast luminescence and high stopping power for hard X-rays, hold great promise for such applications. However, slow luminescence and poor stability caused by surface iodine deficiencies hinder the practical use of γ-CuI. Herein, we treated a γ-CuI single crystal by iodine annealing and SiO2 coating and investigated its crystal structure and luminescence properties in detail. Iodine annealing significantly enhanced the near-band-edge emission of the γ-CuI crystal with an ultrafast decay time of less than 1 ns, while completely suppressing the slow luminescence. Moreover, the SiO2 film effectively prevented the oxidation and decomposition of surface iodine, leading to substantial improvement in luminescence stability. The γ-CuI crystal demonstrated an ultrahigh spatial resolution of 1.5 μm in X-ray imaging, highlighting its potential for ultrafast hard X-ray imaging applications. This study provides insight into the growth, optimization, and application of γ-CuI crystals, advancing the field of scintillator materials.

Interrupted DNA and Slow Silver Cluster Luminescence.

A DNA-silver cluster conjugate is a hierarchical chromophore with a partly reduced silver core embedded within the DNA nucleobases that are covalently linked by the phosphodiester backbone. Specific sites within a polymeric DNA can be targeted to spectrally tune the silver cluster. Here, the repeated (C2A)6 strand is interrupted with a thymine, and the resulting (C2A)2-T-(C2A)4 forms only Ag106+, a chromophore with both prompt (∼1 ns) green and sustained (∼102 μs) red luminescence. Thymine is an inert placeholder that can be removed, and the two fragments (C2A)2 and (C2A)4 also produce the same Ag106+ adduct. In relation to (C2A)2T(C2A)4, the (C2A)2 + (C2A)4 pair is distinguished because the red Ag106+ luminescence is ∼6× lower, relaxes ∼30% faster, and is quenched ∼2× faster with O2. These differences suggest that a specific break in the phosphodiester backbone can regulate how a contiguous vs broken scaffold wraps and better protects its cluster adduct.

Ultrafast and slow luminescence decays at energy transfer from impurity-bound excitons

Different types of ultrafast radiative transitions are considered. The most interesting among them is the case when the radiative transition is accelerated by the configurational transformation of a structural unit where it occurs. Impurity-induced VUV excitation bands of doped Li2B4O7 are attributed to the creation of impurity-bound excitons. When Mn2+ is involved into exciton recombination, the radiative transition in the Mn2+3d5 configuration is accelerated and occurs on a sub-nanosecond time scale. Excitation within the UV bands is connected with energy transfer from the structural units formed by the sensitizers (Cu, Sn) and oxygen to Mn2+. In this case, Mn2+ transitions are not accelerated since its excited state appears after complete relaxation of excitation in the corresponding sensitizer’s unit. Pulsed cathodoluminescence decays are rather slow due to very slow transport of electron–hole pairs and excitons in Li2B4O7.

Light Emission in 2D Silver Phenylchalcogenolates.

Silver phenylselenolate (AgSePh, also known as "mithrene") and silver phenyltellurolate (AgTePh, also known as "tethrene") are two-dimensional (2D) van der Waals semiconductors belonging to an emerging class of hybrid organic-inorganic materials called metal-organic chalcogenolates. Despite having the same crystal structure, AgSePh and AgTePh exhibit a strikingly different excitonic behavior. Whereas AgSePh exhibits narrow, fast luminescence with a minimal Stokes shift, AgTePh exhibits comparatively slow luminescence that is significantly broadened and red-shifted from its absorption minimum. Using time-resolved and temperature-dependent absorption and emission microspectroscopy, combined with subgap photoexcitation studies, we show that exciton dynamics in AgTePh films are dominated by an intrinsic self-trapping behavior, whereas dynamics in AgSePh films are dominated by the interaction of band-edge excitons with a finite number of extrinsic defect/trap states. Density functional theory calculations reveal that AgSePh has simple parabolic band edges with a direct gap at Γ, whereas AgTePh has a saddle point at Γ with a horizontal splitting along the Γ-N1 direction. The correlation between the unique band structure of AgTePh and exciton self-trapping behavior is unclear, prompting further exploration of excitonic phenomena in this emerging class of hybrid 2D semiconductors.

On the analysis of photon arrival time distributions obtained using the pulsed optically stimulated luminescence technique

The objective of this work is to address the analysis of photon arrival time distributions (PATDs) obtained using the pulsed optically stimulated luminescence (POSL) technique in two particular situations: (a) when the interval between pulses is insufficient for the full decay of some of the luminescence components, and (b) in the presence of shallow traps. PATDs are important to characterize the luminescence lifetime of synthetic and natural optically stimulated luminescence (OSL) materials used for dosimetry and in luminescence dating, as well as to separate the OSL components from luminescence centers associated with different luminescence lifetimes. In this study we simulated numerically the PATDs that can be obtained in the presence of fast and slow luminescence centers, where “fast”/“slow” is relative to the pulse width and period, and show that the analysis of these PATDs using semi-empirical equations based on a simple model can lead to wrong results when certain conditions are not satisfied (e.g. full decay of luminescence component between pulses, presence of shallow traps). Modifications to the semi-empirical equations are derived to provide better estimates for the luminescence lifetimes in the conditions simulated. Experimental data on Al2O3:C OSL dosimeters are used to illustrate the relevance of the results.

Light outputs of yttrium doped BaF_2 crystals irradiated with neutrons

The fast luminescence component of barium fluoride (BaF_2) crystals with a subnanosecond decay time can find wide application in particle physics and nuclear physics. However, the slow luminescence component with the 630 ns decay time could cause pile-up signals at a high rate environment. Doping of BaF2 crystals with rare earth elements suppresses the slow emission component, but at the same time the radiation hardness of the crystals deteriorates. This work presents the results of studying crystal samples, both pure BaF2 and those doped with yttrium in a proportion of 1 at.%Y, 3 at.%Y and 5 at.%Y, irradiated with a fast neutron fluence of about 2.3×1014 n/cm2. Their light output and decay kinetics were measured before and after irradiation. It is found that the light output loss of a pure BaF2 crystal after irradiation is about 7%, and the light output loss of yttrium doped samples after irradiation is about two times higher. The measurement results demonstrate that after irradiation the fast component of each sample has a relative light output loss 2–3% larger than the slow one.

Рентгенолюминесцентные свойства пленок оксида цинка на M- и A-плоскостях сапфира

The results of comparative studies of the processes of high-temperature synthesis, luminescence and scintillation characteristics of ZnO films on M(100)- and A(110)-orientation sapphire substrates are presented. It is shown that the use of the magnetron deposition method makes it possible to form, against the background of a continuous film, ensembles of individual [001] ZnO microcrystals with pronounced X-ray luminescent properties. The X-ray luminescence kinetics is characterized by two components: a fast component with a decay time in the order of a nanosecond and a slow luminescence component. The study of the films by photoluminescence spectroscopy revealed the features of the near-band-edge luminescence spectra of the samples, in particular, the presence of various excitonic emission channels. Differences in the spectral parameters of the near-band-edge luminescence band in the case of optical and X-ray excitation are found and interpreted.

X-ray Luminescent Properties of Zinc Oxide Films on the Sapphire M and A-Plane

The results of comparative studies of the processes of high-temperature synthesis, luminescence and scintillation characteristics of ZnO films on M(100)- and A(110)-orientation sapphire substrates are presented. It is shown that the use of the magnetron deposition method makes it possible to form, against the background of a continuous film, ensembles of individual [001] ZnO microcrystals with pronounced X-ray luminescent properties. The X-ray luminescence kinetics is characterized by two components: a fast component with a decay time in the order of a nanosecond and a slow luminescence component. The study of the films by photoluminescence spectroscopy revealed the features of the near-band-edge luminescence spectra of the samples, in particular, the presence of various excitonic emission channels. Differences in the spectral parameters of the near-band-edge luminescence band in the case of optical and X-ray excitation are found and interpreted. Keywords: Films, microcrystals, zinc oxide, X-ray luminescence, photoluminescence, excitonic emission.

Development of CuI:Cl-PS composite scintillator

A promising composite scintillator for used in ultrafast X-ray detection was successfully developed by compounding Cl-doped CuI phosphor with polystyrene (PS) (CuI:Cl-PS), and its crystal structure and luminescence characteristics were investigated in detail. The CuI:Cl-PS composite scintillator only exhibited an intense near-band-edge (NBE) luminescence with a decay time of sub-nanosecond, and the slow luminescence of CuI was entirely suppressed under the excitation of ultraviolet light or X-ray. Furthermore, the intensity of the ultrafast NEB emission for the composite scintillator was not basically deteriorated after storage in air at room temperature for six months. It is expected that the CuI:Cl-PS composite scintillator demonstrates a great potential application in ultrafast hard X-ray detection or imaging.

Multifunctional ZnII–LnIII(Ln = Tb, Dy) complexes based on the amine-phenol ligand with field-induced slow magnetic relaxation, luminescence, and proton conduction

Two new isomorphic ZnII–LnIII–ZnIItrinuclear complexes based on the amine-phenol ligand have been prepared.

X-Ray Luminescence of ZnO Tetrapods Grown in the Presence of Copper and Gold Admixtures in Initial Charge

We investigated the morphology and luminescent properties of ZnO tetrapod powders with copper and gold admixtures, obtained by carbothermal pyrolysis. A broad band in the region of 450–650 nm dominates in the X-ray luminescence spectrum of the samples. There is also a weak edge luminescence band with a maximum at 391 nm. Kinetic measurements showed the presence of both fast (~1 ns) and slow (~850 ns) luminescence components, and the fast component, as a rule, did not exceed 1% of the integrated intensity. The used doping method does not result in the incorporation of copper and gold admixtures into the ZnO lattice. The presence of copper at a concentration of up to 9% does not affect the morphology or luminescence properties of ZnO tetrapods, while gold has such an effect even at a concentration close to 1%.

Optical Properties of Thick Zinc Oxide Films Doped with Gallium and Gold

Samples of thick (30–32 µm) films of pure and gallium- and gold-doped zinc oxide obtained by magnetron sputtering using an uncooled target have been investigated. It is shown that the main changes in the optical properties of undoped thick ZnO films during recrystallization annealing under atmospheric conditions occur for the first 2–3 h. It is found that doping of thick ZnO films with gallium (4 at %) without additional heat treatment doubles the transmittance (to a value of about 97%). At the same time, this introduced gallium concentration leads to concentration quenching of X-ray luminescence. The results of measuring temporal characteristics show that the shapes of X-ray luminescence kinetics of samples with a gold buffer layer after heat treatment and undoped ZnO samples are identical and characterized by a long shoulder of slow luminescence with a characteristic time of about a microsecond and low integrated intensity with a short decay time.

Syntheses, characterization, and slow magnetic relaxation or luminescence properties of three new 2D coordination polymers

Three new 2D coordination polymers (CPs), namely, {[CoL0.5(4,4′-bbib)]}n(1), {[ZnL0.5(4,4′-bbib)]·3DMF·3H2O}n(2) and {[CdL0.5(4,4′-bbib)]·4H2O}n(3), have successfully been constructed by solvothermal method based on H4L, 4,4′-bbib and M(NO3)2 {M = Co (1), Zn (2), Cd (3); H4L = 5,5’-(1,3,6,8-tetraoxobenzo[lmn] [3,8]phenanthrolin-2,7-diyl)bis-1,3-benzenedicarboxylic acid; 4,4′-bbib = 4,4′-bis(benzoimidazo-1-yl)biphenyl}, and studied by structural analysis, magnetic properties and luminescence properties. The structural analysis shows that CPs 1-3 are 4-c 2D network structures with the point symbol of {32.62.72}, which are further expanded into 3D supramolecular architectures by the π … π and hydrogen bonding (O–H⋯O) interactions between the adjacent 2D layers. Magnetic properties show 1 presents a single-molecule magnet (SMM) and slow magnetic relaxation behavior with the energy barrier (Ueff) of 49.73 K and a pre-exponential factor (τ0) of 1.84 × 10−10 s. Luminescent experiments revealed that 2 and 3 can serve as sensors towards Fe3+ and nitroaromatic compounds (NACs) in aqueous medium with high sensitivity and selectivity.

Рентгенолюминесценция тетраподов ZnO, выращенных в присутствии примеси Сu и Au в исходной шихте

The morphology and luminescent properties of ZnO tetrapod powders with Cu and Au impurities obtained by pyrolytic carbothermal synthesis were studied. The X-ray luminescence spectrum of the samples is dominated by a broad band in the range from 450 to 650 nm. A weak band-edge luminescence band with a maximum at 391 nm is also registered. Measurements of the decay kinetics showed the presence of both fast (~ 1 ns) and slow (~ 850 ns) luminescence components, where the fast one generally did not exceed 1% of the integrated intensity. It is shown that with the used doping method, the incorporation of Cu and Au impurities into the ZnO lattice does not occur. In this case, the presence of Cu with a concentration of up to 9% does not affect the morphology and luminescent properties of tetrapods, while Au has an effect even at a concentration close to 1%.

Field-induced slow magnetic relaxation and luminescence thermometry in a mononuclear ytterbium complex

A mononuclear pentagonal bipyramidal YbIII complex functions as a field-induced SIM luminescent thermometer.

Directed UV and X-ray generation in nanomaterials at the optical excitation

Efficient electromagnetic emission of radiation in the spectral range with wavelengths shorter than exciting light wavelength was observed at the nanomaterials excitation by laser pulses. Emission was registered in a visible (blue-green) range, in vacuum UV and in soft X-ray. Luminescence was registered both in the air and in the vacuum chamber. Synthetic opal matrices and nanocomposites on their base (matrices infiltrated with different liquids) were used as samples. Luminescence was excited with the help of different lasers: ruby laser, second harmonic of Nd:YAG laser and copper vapor laser. In the visible range two regimes of luminescence were observed: fast (few μs) and slow (up to 12 s). Slow luminescence was registered at temperatures lower than 110 K. Spectra of X-ray emission were registered. The connection of this emission with the triboluminescence effect is considered.

Improvement of the scintillating properties of ZnO ceramics by the precipitation of initial powder

One of the applications of zinc oxide is a scintillator or phosphor. Both of its emission bands, fast near-band-edge or slow green luminescence, can be used, depending on the application. In any case it is essential to obtain the sample of high transparency in the range of a certain luminescence band. In this work ceramic samples made of undoped ZnO micro- and nanocrystalline powders, where the latter was made by precipitation of initial micro-crystalline powder, were studied. Ceramics showed significant differences in their optical and luminescent properties. The reasons for observed changes are discussed.

Suppression of the slow component of BaF2 crystal luminescence with a thin multilayer filter

The fast component of the barium fluoride (BaF2) crystal luminescence with the emission peak at 220 nm allows those crystals to be employed in fast calorimeters operating in harsh radiation environment. However, the slow component with the emission peak at 330 nm and about 85% of the total emission light could create big problems when working at a high radiation rate. In this work we report results of tests of multilayer filters that can suppress luminescence in the range from 250 nm to 400 nm, which covers most of the BaF2 slow component luminescence. The filters are made by spraying layers of rare earth oxides on a quartz glass substrate. Filters typically comprise 200-220 layers. A few filters were prepared by spraying thin layers on quartz glass. The filters have a peak transmittance of about 70-80% in the range of 200-250 nm. Measurements of the light output of the BaF2 crystal with and without a filter between the crystal readout end and the PMT demonstrate substancial suppression of the slow component. To our knowledge, this kind of filters are produced and tested for the first time.

Lanthanide anthracene complexes: slow magnetic relaxation and luminescence in DyIII, ErIII and YbIII based materials.

Four mononuclear lanthanide complexes, [Ln(depma)2(H2O)6]Cl3·xH2O·yCH3OH [Ln = Dy (1Dy), x = 6, y = 0; Gd (2Gd), x = 3, y = 1; Er (3Er), x = 6, y = 0; Yb (4Yb), x = 3, y = 1; depma = 9-diethylphosphono-methylanthracene], are reported and structurally characterized. The octa-coordinated environment of LnIII is composed of two oxygen atoms from two different depma ligands and six oxygen atoms from each bound water molecule. All four complexes show photoluminescence in the solid state at room temperature, originating from the ligand-centered emissions of depma. Furthermore, slow magnetization relaxation is found in 1Dy, 3Er and 4Yb with the energy barriers (Ueff) of 40.5 K (1 kOe), 9.8 K (1 kOe) and 28.9 K (0.75 kOe), respectively.