Luminescence Decay Kinetics Research Articles

Energy transfer mechanism in infrared-emitting NaYGeO4:Tm3+, Ho3+ phosphors

Two series of NaY0.85Tm0.15-xHoxGeO4 (x = 0.005–0.03) and NaY0.85-xTm0.15HoxGeO4 (x = 0.0–0.055) phosphors have been prepared by the citrate technique. According to XRPD study, all the germanates crystallize in olivine structure and have an orthorhombic lattice, space group Pnma, Z = 4. The diffuse reflectance spectra have been measured and the optical band gap has been estimated. Under 808 nm laser diode excitation, the NaYGeO4:Tm3+, Ho3+ samples exhibit luminescence in the range of 1640–2240 nm, which is caused by 3F4 → 3H6 transition in Tm3+ and 5I7 → 5I8 transition in Ho3+ ions. The highest intensity of holmium lines, while maintaining relatively high intensity of thulium lines, was observed for NaY0.82Tm0.15Ho0.03GeO4, NaY0.815Tm0.15Ho0.035GeO4 samples with the Tm3+/Ho3+ ratio close to 5/1. The luminescence decay kinetics has been studied and the rate of energy transfer from Tm3+ to Ho3+ ions has been calculated. The obtained results indicate an effective energy transfer accelerated by migration due to dipole-dipole interaction. The mechanism of excitation and infrared luminescence in NaYGeO4:Tm3+, Ho3+ phosphors has been proposed.

Energy Transfer Processes in NaBiF4 Nanocrystals Co‐Doped with Tb3+ and Eu3+ Dispersed in Aqueous Solution

AbstractThe synthesis of hexagonal NaBiF4 co‐doped with Tb3+ and Eu3+(NaBi0.75−xTb0.25EuxF4; with x=0, 5, 10, 20 and 30) was achieved via a facile and fast precipitation route at 35 °C. Powder X‐ray diffraction (PXRD) and luminescence spectroscopy have been employed to characterize and investigate the materials. The study of luminescence spectroscopy and decay kinetics of the 5D4 excited state of Tb3+ provides the evidence of a Tb3+→Eu3+ energy transfer process. Sodium citrate has been adopted as capping agent to promote a homogeneous dispersion of the materials into water and to protect the inorganic host, which is water sensitive, from direct contact with this molecule. The comparison of luminescence properties between bare and citrate‐capped samples of NaBiF4 co‐doped with Tb3+ and Eu3+ reveals a marked difference in the Tb3+→Eu3+ energy transfer efficiency, which has been tentatively explained on the basis of a different environment surrounding the lanthanide ions in the two families of compounds.

Influence of {Ce3+ – Mg2+} pairs on the photo- and thermally stimulated luminescence of Mg2+ co-doped Gd3(Ga,Al)5O12:Ce single crystals

Single crystals of Gd3(Ga,Al)5O12:Ce,Mg with different concentration of Mg2+ ions varying from 0 to 0.029 at.% are investigated by the X-ray diffraction, steady-state and time-resolved photoluminescence, and thermally stimulated luminescence (TSL) methods in a wide temperature range (77–510 K). The origin and structure of the luminescence centers are considered. The influence of Mg2+ ions on the structure of the Ce3+-related excited state, the processes taking place in this state, and the TSL characteristics is clarified. At low temperatures, the photoluminescence optical quenching in close {Ce3+ - Mg2+} pairs is found to be responsible for the light yield reduction accompanied with the acceleration of the luminescence decay kinetics. At room temperature, the luminescence quenching can be additionally caused by the thermal ionization of the 5d1 excited state of Ce3+ ion, whose probability increases with the increasing Ga content. The conclusion is made that in order to create the fast scintillator with the maximum light yield, the concentration of intrinsic crystal lattice defects in Gd3(Ga,Al)5O12:Ce,Mg should be minimized, the optimum composition of the host should be chosen, and the balance between the concentrations of the doped Mg2+ and Ce3+ ions should be optimised.

Luminescence of CsLa1-хCeхSiS4 thiosilicate solid solution: From STE to Ce3+ emission

A series of single crystals of CsLa1-хСехSiS4 monophasic solid solution (x = 0–1) has been obtained for the first time by high-temperature flux synthesis. Methods of XRD and chemical analysis, absorption and low-temperature (from T = 5 K) luminescent spectroscopy were used. The results of the band scheme calculating using density functional theory correlate with spectroscopy data. One non-elementary d → f emission band of Ce3+ ions is observed in the region of 520 nm in the luminescence spectra at room temperature at any value of the x parameter. The luminescence decay kinetics of Ce3+ ions upon excitation by a pulsed electron beam, X-ray synchrotron radiation or intracenter photoexcitation is characterized by a nanosecond component. As the parameter x increases, the decay time is reduced from 132 ns (x = 0.005) to 0.88 ns (x = 1). The luminescence decay kinetics upon photoexcitation at x = 0.005–0.12 is characterized by monoexponential decay with τ = 31.4 ± 0.2 ns. Concentration quenching of the Ce3+ ion photoluminescence is not observed up to the value of the parameter x = 0.12; it only appears at x = 1. The anomalously short decay time of the Ce3+ ions luminescence in CsCeSiS4 upon both X-ray excitation and photoexcitation is associated with concentration quenching.At temperature 5 K, new intense bands at 408 and 688 nm in addition to the Ce3+ emission band observed in the photoluminescence spectra of nominally pure CsLaSiS4 or at the lowest parameter value x = 0.005. These bands correspond to the luminescence of self-trapped excitons (STE) and defects. With increasing x parameter, the STE emission band is reabsorbed by the absorption of Ce3+ ions and is quenched due to the resonance energy transfer STE → Ce3+ center. Thermoluminescence glow curves of CsLa1-xCexSiS4 irradiated with X-ray at T = 90 K are characterized by several low temperature intense peaks, which indicates a high concentration of charge carrier traps.

Infrared luminescence properties and energy transfer mechanism in NaYGeO4:Tm3+ powders

Two series of NaY1-xTmxGeO4 olivines with x = 0.005–0.04 and x = 0.0–0.2 have been prepared by the solid state reaction method and citrate technique, respectively. These germanates crystallize in olivine structure and have the orthorhombic lattice, space group Pnma, Z = 4. The diffuse reflectance spectra have been measured and the optical band gap has been estimated. Under 808 nm laser diode excitation, the NaY1-xTmxGeO4 samples yield luminescence in the range of 1300–1600 nm (3H4 → 3F4) and 1600–2200 nm (3F4 → 3H6). The maximum of luminescence integrated intensity has been achieved for the composition NaY0·85Tm0.15GeO4. The luminescence decay kinetics has been explained using migration. The parameters of the cross–relaxation process: 3H4 + 3H6 → 3F4 + 3F4 were obtained taking into account the energy transfer rate between thulium ions. It is shown that the presented materials are characterized by an effective migration-accelerated cross-relaxation process, which occurs as a result of dipole-dipole interactions.

Gd2O3-modulated borate glass for the enhancement of near-infrared emission via energy transfer from Gd3+ to Nd3.

(Li2O)0.20(SrO)0.30(Nd2O3)0.01(B2O3)0.49-x(Gd2O3)x, where x = 0, 3, 5, 7, and 10 mol%, glass was melt-quenched to test it as a laser source in the near-infrared (NIR) region. The structural modification, absorption spectra, Judd-Ofelt (J-O) parameters, luminescence spectra, radiative laser parameters, lifetimes, XRD, and FTIR spectra were studied. Luminescence spectra excited at λexc = 584 nm revealed the highest intensity peak at 1073 nm due to the transition of 4F3/2 → 4I11/2. An important phenomenon of concentration quenching was observed and optimized luminescence was achieved with the sample having the concentration x = 07 mol%. The lifetimes of the donor and acceptor and energy transfer from gadolinium to neodymium were obtained from the luminescence decay kinetics. The findings show that Nd-doped Gd2O3-modified glass materials have potential as NIR laser sources.

High concentration Eu3+ doped yttria-stabilized zirconia ceramics

The series of yttria-stabilized zirconia (YSZ) ceramics doped with high Eu3+ ions concentration (up to 15 wt%) were successfully fabricated by Spark Plasma Sintering (SPS) technique for the first time. The effect of europium concentration and atmospheric annealing on the optical, structural, and luminescent properties has been studied in detail. The combination of XRD and EDS data allows to find two phases in tested YSZ:Eu ceramics such as ZrO2 and Zr2O. The highest transmission values were achieved about 63% at 600 nm for the 10 wt% of Eu2O3 doped YSZ ceramics without annealing. When the annealing temperature changes from 1300° to 1600°C the transmission values increase to 70%. An analysis of the photoexcitation and photoluminescence spectra showed that the main excitation bands are determined by the direct excitation of the 7F0 ground state to higher 4 f levels with following radiation transitions in Eu3+ ions. The optimal Eu3+- dopant concentration in YSZ ceramics was established and the process of emission quenching was discussed. The luminescence decay kinetics are approximated by the single or sum of two exponential functions in dependence of Eu3+ ions concentrations.

Luminescence Dynamics of Single Self-Assembled Chains of Förster (FRET)-Coupled CdSe Nanoplatelets.

Self-assembled linear chains of CdSe nanoplatelets are known to exhibit highly efficient Förster resonant energy transfer (FRET) leading to fast exciton diffusion between platelets. Here, we compare the luminescence decay dynamics of single nanoplatelets, clusters of a few platelets, and self-assembled chains. As the number of stacked platelets is increased, we show that the luminescence decay becomes faster, which can be interpreted as the FRET-mediated effect of quenchers: excitons may diffuse to nearby quenchers so that their decay rate is increased. On the other hand, a minor slow decay component is also observed for single platelets, corresponding to trapping-detrapping mechanisms in nearby trap states. The contribution of the slow component is enhanced for the platelet chains. This is consistent with a FRET-mediated trapping mechanism where the excitons would diffuse from platelet to platelet until they reach a trap state. Finally, we develop toy models for the FRET-mediated quenching and trapping effects on the decay curves and analyze the relevant parameters.

Influence of irradiation with fast electron beam on energy transport in praseodymium-ion doped phosphates

This paper reports the spectroscopic properties of praseodymium-doped phosphates, KLuP2O7, Sr9Sc(PO4)7, K3Lu(PO4)2 doped with Pr3+ ions. Spectra of photoluminescence (PL) upon selective UV photon excitation, PL excitation spectra as well as luminescence spectra and decay kinetics upon pulse synchrotron X-ray excitation were studied. Recordings of luminescence spectra were done with pure samples and after irradiating with fast electrons (E = 10 MeV) using linear electron accelerator. The absorbed dose varied in the range of 150–300 kGy. Pure samples demonstrated three typical channels of emission: interconfigurational d – f transitions, intraconfigurational f – f transitions and defect-related luminescence. After irradiating, two scenarios of changing optical properties were investigated: increasing of defect-related luminescence impact in total light output and “suppressing” of defect-located energy emission.

Structural features and optical-luminescent properties of the Pb-containing germanate and silicate oxyfluoride glasses

The XRD, IR transmission, EPR, optical absorption, luminescence spectra and decay kinetics in new un-doped 0.5PbO–0.3GeO2–0.2AlF3 and 0.53PbO–0.226SiO2–0.244AlF3 glasses were investigated. The XRD patterns were analysed in order to obtain the radial distribution functions and define the average interatomic distances and coordination numbers in the network of investigated glasses. The IR transmission, EPR, and UV–vis optical absorption spectra of the studied glasses were interpreted. Optical band gap and Urbach energy were obtained from analysis of the fundamental absorption edge. Under UV photoexcitation the 0.5PbO–0.3GeO2–0.2AlF3 and 0.53PbO–0.226SiO2–0.244AlF3 glasses demonstrate broad emission band at 493 nm and 499 nm, respectively. Fast (band-to-band recombination) and slow (recombination with a contribution of defects levels) mechanisms of intrinsic luminescence have been proposed from a detailed analysis of luminescence spectra and decay kinetics curves. The CIE chromaticity diagram shows a variation in emission colour of studied glasses with the change in their composition.

Керамические радиационно стойкие сцинтилляторы для регистрации высокоэнергетического излучения

Complex oxides of Y3Al5O12, Gd(Nb,Ta)O4, (Zr,Hf,Y)O2, (Zr,Y)O2, activated with trivalent rare earth ions Nd3+, Eu3+ and Tb3+ have been studied in terms of their luminescent properties. These materials are promising scintillators with high radiation, chemical, and mechanical stability. The aim of the work was to develop ceramic radiation-resistant scintillators based on oxides activated by rare-earth ions. The study included: an evaluation of changes in the intensity and kinetics of luminescence decay from single crystal samples to ceramics; a study of the complete or partial replacement of light elements by heavier ones effect on the luminescent properties; a study of the possibility of using a sensitizer to increase the luminescence yield when luminescence is excited by an electron beam of medium energies.

Orthogonal luminescence lifetime encoding by intermetallic energy transfer in heterometallic rare-earth MOFs

Lifetime-encoded materials are particularly attractive as optical tags, however examples are rare and hindered in practical application by complex interrogation methods. Here, we demonstrate a design strategy towards multiplexed, lifetime-encoded tags via engineering intermetallic energy transfer in a family of heterometallic rare-earth metal-organic frameworks (MOFs). The MOFs are derived from a combination of a high-energy donor (Eu), a low-energy acceptor (Yb) and an optically inactive ion (Gd) with the 1,2,4,5 tetrakis(4-carboxyphenyl) benzene (TCPB) organic linker. Precise manipulation of the luminescence decay dynamics over a wide microsecond regime is achieved via control over metal distribution in these systems. Demonstration of this platform’s relevance as a tag is attained via a dynamic double encoding method that uses the braille alphabet, and by incorporation into photocurable inks patterned on glass and interrogated via digital high-speed imaging. This study reveals true orthogonality in encoding using independently variable lifetime and composition, and highlights the utility of this design strategy, combining facile synthesis and interrogation with complex optical properties.

Bi3+ - doped garnets as possible ultraviolet persistent phosphors

Ultraviolet (UV) persistent luminescence (afterglow) and thermally stimulated luminescence observed in the 3.6–4.2 eV energy range are studied for microcrystalline powders of the Bi3+-doped Lu3Ga5O12, Y3Ga5O12, and Ca3Ga2Ge3O12 garnets after their selective UV irradiation at 295 K in the 4–6 eV energy range. Emission and excitation spectra and decay kinetics of the persistent luminescence, as well as the luminescence intensity dependence on the irradiation duration, are measured at 295 K. No UV emission has been observed in the afterglow spectrum of the Gd3Ga5O12:Bi, Lu3Al5O12:Bi, and Y3Al5O12:Bi garnets. The processes resulting in the appearance of the UV persistent luminescence in the investigated Bi3+-doped garnets are discussed. The conditions are formulated which ensure the appearance of this phenomenon in Bi3+-doped compounds and, thus, could inspire the discovery of new effective UV persistent phosphors.

Perculiarities of yellow luminescence decay kinetics in LiF-UO-=SUB=-2-=/SUB=- crystals

A fast component, on the order 387 ns (300 K), has been detected in the decay kinetics of the yellow luminescence (563 nm) in LiF-UO2 crystals. It is shown that the emitting centers are anisotropic formations oriented in the crystal lattice along the second-order symmetry axes (C2) using the method of azimuthal dependence of the luminescence polarization. A model of the radiating centre is proposed and the position of the oxygen defect excited level is determined, from which the transition of an electron to the conduction band occurs. The luminescence (387 ns) from of the U5+ ion is observed as a result of electron transfer from oxygen ion to the excited U6+ level. The subsequent hole localization on U5+ in the ground state is accompanied by the reduction of the U6+ ion, that luminescence is observed in the green region of the spectrum (523 nm) with time decay 100 microsecond. Keyword: decay kinetics of luminescence, polarization, LiF-UO2 crystals.

Особенности люминесценции керамики на основе кубического (ZR-=SUB=-0.82-x-=/SUB=-HF-=SUB=-x-=/SUB=-Y-=SUB=-0.17-=/SUB=-Eu-=SUB=-0.01-=/SUB=-)O-=SUB=-1.91-=/SUB=-

The ceramics based on cubic (Zr0.82-xHfxY0.17Eu0.1)O1.91 with different contents of hafnium were studied. In the work, the elemental composition of the samples was obtained, the cathodoluminescence (CL) spectra and decay kinetics of europium luminescence were studied. The researched showed increase in the content of hafnium doesn’t affect the position and number of observed bands in the luminescence spectrum. The electric dipole and magnetic dipole radiative transitions ratio was estimated for all samples. It’s demonstrated that a decrease in the local symmetry of the europium ion associated with an increase in the hafnium content. It’s shown the 5D0-7F1 transition Eu3+ decay time doesn’t depend on the hafnium content, but varies significantly in different regions of the sample, which can be attributed to the influence of grain boundaries.

Ceria nanomaterials containing ytterbium: low and high concentration - luminescence analyzed in the near infrared region.

Lanthanide based ceria nanomaterials are important practical materials due to the redox properties that are useful in the avenues pertaining to technology and life sciences. Sub 10 nm spherical and highly monodisperse Ce1-xYbxO2-y (0.04 ≤ x ≤ 0.22) nanoparticles were synthesized by thermal decomposition, annealed separately at 773 K and 1273 K for 2 hours and characterized. Elemental mapping for Yb3+ doped ceria nanoparticles shows homogeneous distribution of Yb3+ atoms in the ceria with low Yb3+ content annealed at 773 K and 1273 K for 2 hours. However, clusters are observed for 773 K annealed ceria samples with high concentration of Yb3+. These clusters are not detected in 1273 K annealed nanomaterials. Introducing small amounts of Yb3+ ions into the ceria lattice as spectroscopic probes can provide detailed information about the atomic structure and local environments allowing the monitoring of small structural changes, such as clustering. The emission spectra observed at room temperature and at 4 K have a manifold of bands that corresponds to the 2F5/2 → 2F7/2 transition of Yb3+ ions. Some small shifts are observed in the Stark splitting pattern depending on the sample and the annealing conditions. The deconvolution by PARAFAC analysis yielded luminescence decay kinetics as well as the associated luminescence spectra of three species for each of the low Yb3+ doped ceria samples annealed at 773 K and one species for the 1273 K annealed samples. However, the ceria samples with high concentration of Yb3+ annealed at the two temperatures showed only one species with lower decay times as compared to the low Yb3+ doped ceria samples.

Рентгенолюминесценция пленок ZnO толщиной более 100 μm

For the first time, the work presents a thin-film X-ray scintillator based on ZnO with a thickness of more than 100 μm with luminescence decay kinetics of the order of 1.1 ns (including the width of the exciting pulse). The absorption edge of the film scintillator is shown to be located in the region 388 nm. The total transmittance of the sample in the visible and near infrared region reaches 40%. The X-ray luminescence spectrum is represented by two intense bands: a narrow band of excitonic nature with a maximum in the region of 389 nm and a wide band of green luminescence related to intrinsic defects.

Investigation of ion-ion (Nd–Nd) interaction mechanisms in Sr3LaNb3O12:Nd3+ crystals

The spectral-kinetic characteristics of Nd3+ optical centers (A, B, C centers) in Sr3LaNb3O12 crystals are studied by selective laser spectroscopy technique. It is found that the luminescence decay of A centers (donors) at the first stage is quenched by an ordered ensemble of acceptors (B centers) while the second stage is disordered and follows the Förster law.The macro-(γ(N1) = 55 cm−1/2, γ(N2) = 95 cm−1/2) and microparameters (CDA = 4.5⋅10−40 cm6/s) of the ion–ion (Nd3+–Nd3+) interaction are calculated using the static quenching theory. The closest distance between neodymium ions involved into the ion–ion (A and B optical centers) interaction is calculated to be Rmin. = 0.45 nm, and the boundary time at which the ordered luminescence quenching stage changes for disordered one is determined as tbound. ∼19 μs. It is shown that the A centers luminescence quenching mechanism is the dipole–dipole (S = 6) one.The Nd3+ luminescence build-up and decay kinetics in ensemble of acceptor centers (B centers) in case of unequal donor and acceptor lifetimes (τD <τA) are determined.

Upconversion FRET quantitation: the role of donor photoexcitation mode and compositional architecture on the decay and intensity based responses

Lanthanide-doped colloidal nanoparticles capable of photon upconversion (UC) offer long luminescence lifetimes, narrowband absorption and emission spectra, and efficient anti-Stokes emission. These features are highly advantageous for Förster Resonance Energy Transfer (FRET) based detection. Upconverting nanoparticles (UCNPs) as donors may solve the existing problems of molecular FRET systems, such as photobleaching and limitations in quantitative analysis, but these new labels also bring new challenges. Here we have studied the impact of the core-shell compositional architecture of upconverting nanoparticle donors and the mode of photoexcitation on the performance of UC-FRET from UCNPs to Rose Bengal (RB) molecular acceptor. We have quantitatively compared luminescence rise and decay kinetics of Er3+ emission using core-only NaYF4: 20% Yb, 2% Er and core-shell NaYF4: 20% Yb @ NaYF4: 20% Yb, 5% Er donor UCNPs under three photoexcitation schemes: (1) direct short-pulse photoexcitation of Er3+ at 520 nm; indirect photoexcitation of Er3+ through Yb3+ sensitizer with (2) 980 nm short (5–7 ns) or (3) 980 nm long (4 ms) laser pulses. The donor luminescence kinetics and steady-state emission spectra differed between the UCNP architectures and excitation schemes. Aiming for highly sensitive kinetic upconversion FRET-based biomolecular assays, the experimental results underline the complexity of the excitation and energy-migration mechanisms affecting the Er3+ donor responses and suggest ways to optimize the photoexcitation scheme and the architecture of the UCNPs used as luminescent donors.

Estimation of yield and decay kinetics of intraband luminescence in multiple-parabolic-branch-band model with account of phonons

The emission spectrum of electron intraband luminescence was calculated for a dielectric crystal with conduction band consists of multiple parabolic branches. This shape of this spectrum adequately correspond to the CsI experimental spectra in the photon energy region ≥ 1.2 eV. The calculated total quantum yield of intraband luminescence of CsI is about 78 photons collected by the silicon photomultiplier per 1 MeV of deposited energy of ionizing radiation. This value is about two times higher than the experimental one, the difference is due to the simplification of the model. It was shown that characteristic times of intraband luminescence are about 1 ps.