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Compared to halides Cs2HfX6 (X = Cl, Br, I) with a vacancy‐ordered cubic double perovskite structure, the halide Cs2HfF6 (CHF), with a hexagonal Bravais lattice, possesses a higher mass density and chemical stability for radiation detection. Luminescence properties and energy transfer mechanisms of rare‐earths‐doped CHF materials are studied here. The structure of CHF is identified as a new type of vacancy‐ordered hexagonal perovskite, with the same type of building blocks of the double perovskite but stacked with single layers. Density‐functional theory calculations reveal a large bandgap of CHF. A broad emission is observed from the pristine CHF host, which is suggested to be associated with self‐trapped excitons (STEs). A series of rare‐earths‐doped materials are designed utilizing the STE emissions, and efficient energy transfers from STEs and Tb3+ to Eu3+ are achieved for tunable emissions. The codoped material shows stable emission under X‐ray irradiation, with 10.2% reduction from its initial emission intensity, associated with possible structural evolution by radiation‐induced deformation of the soft host. The radiation responses of singly and codoped materials are evaluated, and the codoped material is found to be more sensitive to the radiation energy than the singly doped or pristine CHF for radiation detection. [ABSTRACT FROM AUTHOR]

Host–guest doping strategy greatly facilitates and expands the scope of construction of organic phosphorescence materials. Herein, triphenylamine with excellent crystallinity is chosen as the host, and four guests with 2–4 triphenylamine repeating units are chosen as the guests. The similarity in molecular structures of the host and guests simplifies the exploration of the luminescence mechanism in the doped system. The doped materials display strong room temperature phosphorescence (RTP) with above 200 ms lifetimes and 30% quantum yields. In addition, the doped system emits blue fluorescence under mechanical stimulation, that is, shows a phenomenon of mechanoluminescence (ML). The experimental results prove that the host plays different roles in different luminescence processes. In the photophosphorescence process, the triplet energy level of the host assists the guest excitons to undergo intersystem crossing. Meanwhile, in the ML process, the energy generated as a result of piezoelectric property of the host crystal is transferred to the guest, causing the guest molecules to emit fluorescence. This work is significant for the construction of doped materials with multiple luminescence properties, including RTP and ML. [ABSTRACT FROM AUTHOR]

Exploration of upconversion luminescence from lanthanide emitters through energy migration has profound implications for fundamental research and technology development. However, energy migration-mediated upconversion requires stringent experimental conditions, such as high power excitation and special migratory ions in the host lattice, imposing selection constraints on lanthanide emitters. Here we demonstrate photon upconversion of diverse lanthanide emitters by harnessing triplet exciton-mediated energy relay. Compared with gadolinium-based systems, this energy relay is less dependent on excitation power and enhances the emission intensity of Tb3+ by 158-fold. Mechanistic investigations reveal that emission enhancement is attributable to strong coupling between lanthanides and surface molecules, which enables fast triplet generation (<100 ps) and subsequent near-unity triplet transfer efficiency from surface ligands to lanthanides. Moreover, the energy relay approach supports long-distance energy transfer and allows upconversion modulation in microstructures. These findings enhance fundamental understanding of energy transfer at molecule-nanoparticle interfaces and open exciting avenues for developing hybrid, high-performance optical materials. Photon upconversion in lanthanide-doped nanoparticles enables important technological developments. Here the authors demonstrate a mechanism leading to enhanced upconversion emission in core-shell nanoparticles, and long-distance energy transfer between nanoparticles, through triplet state population of an organic surface ligand. [ABSTRACT FROM AUTHOR]

• A series of Mn-doped A 2 PbBr 4 2D perovskites are synthesized and the luminescence properties of Mn2+ ions in related to the A-site cations is explored. • The highest efficiency of the energy transfer from excitons to Mn2+ reaches as high as 78.08 % in (PPA) 2 PbBr 4 :60 % Mn2+ 2D perovskite. • The luminescence mechanism of Mn-doped (PPA) 2 PbBr 4 perovskite with different Mn2+ concentrations are investigated by temperature dependent PL spectra. The incorporation of Mn2+ ions has been widely used to modulate optical properties of two-dimensional (2D) organic-inorganic hybrid perovskites (OIHPs). However, the luminescence mechanism of Mn2+ ions that is related to the A-site cations remains largely unexplored. Herein, we report the synthesis of a series of Mn-doped A 2 PbBr 4 (A = C 6 H 5 (CH 2) n NH 3 , n = 1,2,3,4,) 2D perovskites. The (C 6 H 5 (CH 2) 3 NH 3) 2 PbBr 4 ((PPA) 2 PbBr 4) 2D perovskite exhibited a maximum photoluminescence (PL) quantum yield of 67 %, a prolonged PL lifetime of 0.75 ms, and the highest energy transfer efficiency of 78.07 %. Furthermore, we systematically investigated the luminescence properties of Mn-doped (PPA) 2 PbBr 4 perovskite with different Mn2+ concentrations. The temperature dependent PL spectra indicate a thermalized de-trap process of self-trapped exciton at high temperatures and the presence of permanently shallow defect states in highly doped samples with lower activation energy. We reported the luminescence properties of Mn-doped 2D organic-inorganic hybrid perovskites, with a particular focus on the (PPA) 2 PbBr 4 perovskite material. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, we fabricated Cs 3 ScCl 6 crystals doped with different concentrations of Ce and investigated their luminescence properties. In both the photoluminescence (PL) and scintillation spectra, emission bands attributable to Ce3+ 5d–4f transition were observed. The PL temporal profiles revealed decay time constants of ~35 ns, which are typical values for Ce3+ 5d–4f transition. In the scintillation temporal profiles, two decay components were observed. The fast and slow components could be attributed to Ce3+ 5d–4f luminescence and self-trapped excitons (STEs) or a slow energy transfer from STEs to Ce3+, respectively. The maximum light yield was 9200 photons/MeV for a Ce concentration of 0.5 mol%. [ABSTRACT FROM AUTHOR]

We discuss exciton transport and energy transfer in organic solar cells based on dicyanovinyl-terthiophene (DCV3T). Time-resolved surface luminescence quenching experiments on double layers of DCV3T and zinc-phthalocyanine as luminescence quencher are analyzed in the framework of a three-level luminescence model with an initially absorbing state of short lifetime that relaxes to a longer living emitting state. Luminescence quenching of the emitting state is assigned to Förster-type energy transfer with an apparent Förster radius of 2.1 nm, which is in accordance with the Förster radius obtained from the spectral overlap integral. A diffusion based analysis for the emitting state yields a diffusion length of Le=6.9 nm. The short living initial state is quenched by diffusion of the excitons to the interface with a diffusion length of La=5.3 nm. External quantum efficiency measurements of the photocurrent in a corresponding organic solar cell structure evaluated with a two-level diffusion model give a diffusion length of LEQE=6.0 nm, whereas a two-level model for stationary luminescence quenching yields a diffusion length of Lcw=12 nm. This suggests that only one type of the excitons contributes to the photocurrent. [ABSTRACT FROM AUTHOR]

Ce+3 doped CsLaSiS 4 single crystals were synthesized using high-temperature flux synthesis. XRD analysis showed that the products are isostructural to CsLaSiS 4 and crystallize in orthorhombic space group Pnma. Absorption spectra were studied at room temperature, and photoluminescence properties were examined in the temperature range of 5–310 K. The energy of interband transitions E g = 3.75 eV was determined at room temperature in the Tauc model. At room temperature, only a non-elementary d → f emission band of Ce+3 ions was observed in the 520 nm region. The luminescence kinetics upon excitation by a pulsed cathode beam or X-ray synchrotron radiation exhibited a dominant nanosecond component. Decay time, as well as build-up time, decreased with increasing concentration of Ce+3 ions. Concentration quenching of Ce+3 emission was not observed up to 11.9 mol% of Ce+3 ions. At a low temperature of 5 K, new wide emission bands at 422 and 688 nm appeared in the photoluminescence spectrum. It is shown that the 422 nm band in the photoluminescence spectrum corresponds to host emission, specifically the luminescence of self-trapped excitons (STE). The 688 nm emission band corresponds to defect-related luminescence. STE emission is quenched according to the Mott law at temperatures above 26 K with an activation energy of 20 meV. An efficient energy transfer channel from the STE to the Ce+3 ion via the radiative resonance mechanism is observed. The emission of Ce+3 ions and defect-related luminescence can be excited by the intracenter way, due to electron-hole recombination, or by the creation of defect bound excitons. Based on the obtained spectroscopic data, a band scheme illustrating the processes of relaxation of electronic excitations at T = 5 K in Ce+3 doped CsLaSiS 4 crystals is proposed. [Display omitted] • Ce+3 doped CsLaSiS 4 single crystals were obtained through high-temperature flux synthesis. • Inter configurational d-f transitions in Ce3+ ions were studied upon both UV- and X-ray excitation. • Luminescence kinetic studies were conducted using a pulsed cathode beam and X-ray synchrotron radiation. • Self-trapped excitons, defect-bound excitons, and impurity luminescence were observed at T = 5 K. [ABSTRACT FROM AUTHOR]

Exciton diffusion is of great importance to the future design of high efficiency organic photovoltaics. Exciton diffusion studies require accurate experimental techniques. This paper addresses two important complications that can arise in exciton diffusion length measurements made by analyzing luminescence from thin films on quenching substrates: namely, the effects of optical interference and of energy transfer to the quencher. When there is modest contrast in the refractive indices of the quencher and organic material, as is the case for titania or C60 and most organic materials, interference effects can overwhelm the measurement, thereby making it impossible to accurately determine the diffusion length of excitons in the organic material. We show that this problem can be fully eliminated by using thin (<5 nm) quencher films. The second complication that can occur is energy transfer to the quenching layer. We model the effect this has when fullerenes are used as quenchers. If energy transfer was ignored, one would falsely measure exciton diffusion lengths that are much greater than, and in some cases more than double, the actual diffusion length. Using titania as a quencher we eliminate the possibility of energy transfer, and by using thin titania films we eliminate the effects of interference and accurately measure a diffusion length of 6±1 nm for the commonly used polymer poly[2-methoxy,5-(3,7-dimethyloctyloxy)]-1,4-phenylenevinylene. [ABSTRACT FROM AUTHOR]

Lead-free double perovskites have superb luminescence properties for broad applications. However, increasing or improving near-infrared (NIR) photoluminescence (PL) is still a challenge. In this paper, a high-performance microcrystal is designed based on Tm3+ heavily doped Cs 2 Ag 0.6 Na 0.4 In 0.9 Bi 0.1 Cl 6 (CANIBC), which realize both the self-trapped excitons (STEs) and Tm3+ NIR emission. The emission mechanism and energy transfer (ET) process are studied by steady-state and time-resolved PL spectra. The ET efficiency from STEs to Tm3+ can reach 38.3 %, and the NIR PL quantum yield of Tm3+ can reach 22.7 %. Meanwhile, the PL spectra of Tm3+-doped CANIBC microcrystals (MCs) with different concentrations are used to investigate their temperature sensing properties based on both fluorescence intensity ratio (FIR) and lifetime. Based on the FIR, relative sensitivity (S r) can reach 2.93 % K−1 at 303 K. Moreover, based on lifetimes, S r can maintain more than 1.55 % K−1 from 303 to 453 K, and maximum S r can also achieve 2.38 % K−1 at 360 K. These excellent luminescence and sensing properties offer greater development potential in the field of NIR phosphor and thermometry. • As-synthesized materials present both perovskite and Tm3+ emission. • Energy transfer efficiency is obtained from the peak decompositions. • Near-infrared photoluminescence quantum yield of Tm3+ can reach 22.7 %. • Sensitivity of fluorescence intensity ratio reaches 2.93 % K−1 at 303 K. • Sensitivity of lifetime sensing sustains beyond 1.55 % K−1 from 303 to 453 K. [ABSTRACT FROM AUTHOR]

The paper contains detailed crystal structure and photoluminescence studies of the Bi3+ and Bi3+-Eu3+ co-doped Gd 3 Ga 5 O 12 (GGG) garnet. The studied materials have been synthesized in the form of microcrystalline powders by the common solid-state reaction method. Precise crystal structure parameters were derived from the X-ray powder diffraction data. Photoluminescence studies were done by the steady-state and time-resolved techniques in the 4.2–400 K temperature range. The studied materials show no UV luminescence caused by electronic transitions of a Bi3+ ion. The observed luminescence in visible is interpreted by excitons localized around Bi3+ ions. In particular, two emission bands located at 2.55 eV (486 nm) and 2.05 eV (605 nm) at 4.2 K were revealed. The main emission band at 2.55 eV is attributed to the triplet relaxed state of excitons localized around single (regular) Bi3+ ions, whereas the weaker band at 2.05 eV is related to some associates of a single Bi3+ ion with a crystal lattice defect. The performed studies for Bi3+-Eu3+ co-doped samples indicate that the energy transfer from Bi3+ to Eu3+ is radiative and is caused by reabsorption of the Bi-related exciton emission by Eu3+ ions. The studied materials were also characterized as a single-phase converting phosphor for near-UV excited white LEDs. The possibility of the emission color tuning from blue to orange-red at UV excitation by the way of changing of Bi3+ and Eu3+ concentrations was shown. [ABSTRACT FROM AUTHOR]

Abstract The A′ luminescence band due to the In+ center in co-doped NaCl:I−,In+ crystals is observed even under excitation at the absorption band due to the I− center, indicating the energy transfer processes from the I− center to the In+ center. The temporal profile of the exciton luminescence bound to the I− center in the co-doped NaCl:I−,In+ crystals exhibits the faster decay than that of the bound exciton luminescence in single-doped NaCl:I− crystals. The reduction of the decay profile is observed even in the samples with an average distance of about 20 nm between two kinds of the impurity centers. The average distance is significantly larger than the critical distance of 3.0 nm for resonance energy transfer, which is estimated from the overlap between the bound exciton luminescence band and the C absorption band due to the In+ center. The facts indicate that the energy transfer process is not resonant-type and/or through reabsorption of the luminescence. We discuss the energy transfer mechanism from the I− to In+ centers in the NaCl:I−,In+ crystals. [ABSTRACT FROM AUTHOR]

We have considered the resonant nonradiative energy transfer in hybrid associates of thionine dye (TH+) molecules and Ag2S colloidal quantum dots (QDs) passivated with thioglycolic acid (Ag2S/TGA) and Ag2S QDs stabilized with gelatin (Ag2S/Gel). Used samples of Ag2S QDs possess luminescence, which arises by the exciton mechanism, as well as by the recombination mechanisms of holes with electrons localized at luminescence centers and of electrons with holes localized at the luminescence centers. The quenching of luminescence of Ag2S/TGA QDs (1.8 nm) with a maximum at 630 nm and a decrease in the luminescence lifetime from 13.7 to 6.5 ns, which occurs upon association with TH+ molecules, have been established. On the contrary, for associates of Ag2S/TGA QDs (5.5 nm) with TH+ molecules, we have observed the quenching of luminescence of the dye and a decrease in the lifetime of this luminescence from 0.43 to 0.3 ns, as well as an enhancement of luminescence of QDs. In the case of hybrid association with TH+ molecules, the luminescence enhancement of Ag2S/Gel QDs (1.6 nm) has been established, which results from the recombination of free holes with electrons localized at luminescence centers. Based on our analysis of the luminescence kinetics of the dye, we have inferred the occurrence of resonant nonradiative energy transfer from TH+ molecules to centers of recombination luminescence in Ag2S/TGA (5.5 nm) and in Ag2S/Gel (1.6 nm) QDs with its maxima at 950 and 1205 nm, respectively. For Ag2S/TGA QDs (2.2 nm), which luminesce with a maximum at 620 nm by the exciton mechanism, we have observed a significant overlap both between the luminescence spectra of QDs and TH+ and between their absorption spectra. Close parameters of the luminescence kinetics for both the initial components and their associates indicate the energy transfer, which is realized in opposite directions. [ABSTRACT FROM AUTHOR]

Single-component phosphors with efficient and stable white-light emission are designed to overcome the trouble of various deteriorations and reabsorptions in the conventional mixing multiple-component phosphors for lighting applications. Here, Er3+ is introduced partially into the double perovskite Cs 2 Ag(Na)In(Bi)Cl 6 lattice to tune white-light emission through adjusting its content. The as-synthesized material itself possesses strong tunable white-light emission under irradiation by 405 nm light due to the combination of self-trapped excitons emission and efficient characteristic emission of Er3+. Steady-state photoluminescence (PL) and time-resolved PL spectra are measured to characterize luminescence properties and clarify the luminescence mechanism. The PL quantum yield of undoped Cs 2 Ag(Na)In(Bi)Cl 6 can achieve 64%. After doping 2 mmol Er3+, energy transfer efficiency from perovskite to Er3+ can reach 30.1%, with an improved PL quantum yield of 71%. The full-spectrum white-light emission can be realized by the Er3+ doped Cs 2 Ag(Na)In(Bi)Cl 6 phosphors-converted 410–420 nm light-emitting diode. Commission International de I'Eclairage (CIE) color coordinates of white light can be improved from (0.47, 0.41) to (0.33, 0.35) with the increase of Er3+ content, and the corresponding color temperature is tuned from 2532 to 5760 K. These characteristics demonstrate that Er3+ doped Cs 2 Ag(Na)In(Bi)Cl 6 phosphors are promising single-component white-light phosphors for next-generation lighting. [Display omitted] • The as-synthesized materials possess both perovskite and Er3+ emission. • Energy transfer from perovskite to Er3+ leads to Er3+ emission. • Energy transfer efficiency from self-trapped excitons to Er3+ can reach 30.1%. • Commission International de I'Eclairage (CIE) can be improved to (0.33, 0.35). [ABSTRACT FROM AUTHOR]

Temperature dependence of the exciton and luminescence intensities in Mn-doped CdS/ZnS quantum dots (QDs) emitting both exciton and dopant luminescence simultaneously was studied in the temperature range 77-320 K. With increasing temperature, exciton luminescence intensity decreased as a result of the increased charge carrier trapping, similar to the usual undoped QDs. In contrast, the sensitized Mn luminescence intensity increased with increasing temperature despite the decrease in the exciton population available for the sensitization. The observed opposite temperature dependence of the exciton and Mn luminescence indicates that the exciton-Mn energy transfer rate should increase with temperature significantly more rapidly than the charge carrier trapping. Temperature shift of the bandgap of the host QD and the energy of accepting d-d transition, resulting in the variation of the donor-acceptor spectral overlap, is considered responsible for the large temperature dependence of the energy transfer rate in Mn-doped QDs. [ABSTRACT FROM AUTHOR]

Temperature dependence of the exciton and luminescence intensities in Mn-doped CdS/ZnS quantum dots (QDs) emitting both exciton and dopant luminescence simultaneously was studied in the temperature range 77-320 K. With increasing temperature, exciton luminescence intensity decreased as a result of the increased charge carrier trapping, similar to the usual undoped QDs. In contrast, the sensitized Mn luminescence intensity increased with increasing temperature despite the decrease in the exciton population available for the sensitization. The observed opposite temperature dependence of the exciton and Mn luminescence indicates that the exciton-Mn energy transfer rate should increase with temperature significantly more rapidly than the charge carrier trapping. Temperature shift of the bandgap of the host QD and the energy of accepting d-d transition, resulting in the variation of the donor-acceptor spectral overlap, is considered responsible for the large temperature dependence of the energy transfer rate in Mn-doped QDs. [ABSTRACT FROM AUTHOR]

Particular features and quenching mechanisms of exciton luminescence of water-soluble nanocomposites that are formed as a result of the interaction of surface charged semiconductor quantum dots (QDs) CdSe/ZnS ( d = 2.8 nm) and cationic porphyrins (HTMPyrP and ZnTMPyrP) have been studied theoretically and experimentally. It has been found that, in CdSe/ZnS⊕Porphyrin conjugates, there occurs long-range inductive resonance electronic excitation energy transfer from surface modified (with thioglycolic or mercaptoundecanoic acid) QDs to porphyrins, which is accompanied by quenching of the exciton luminescence of QDs and an increase in the fluorescence intensity of porphyrin. It has been shown that, when mercaptoundecanoic acid is used as a QD shell, the QD luminescence quenching efficiency by porphyrins follows the Förster-Galanin theory and depends on the overlap integral between the CdSe/ZnS luminescence band and the absorption spectra of free-base porphyrin HTMPyrP and its metal complex ZnTMPyrP. It has been revealed that, as the QDs ↔ Zn-porphyrin intercenter distance decreases from 39.1 (mercaptoundecanoic acid) to 30.1), a considerable QD luminescence quenching is observed; however, the energy transfer efficiency substantially decreases, from 55% in the former case to 23% in the latter one. Based on the spectral-luminescent data and quantum-chemical calculations, it has been found that the chemical change of HTMPyrP in the structure of the complex with CdSe/ZnS QDs passivated by thioglycolic or mercaptoundecanoic acid is caused by the formation of a metal complex ZnTMPyrP. Based on calculations of the redox-potentials, it has been concluded that the low luminescence quantum yield of CdSe/ZnS QDs passivated by residues of mercaptocarboxylic acids S(CH)COO and its dependence on the number of CH groups are related to the possibility of photoinduced electron transfer from the HOMO of passivating molecules to QDs (QD* ⇐ S(CH) nCOO hole transfer). It has been shown that the quenching of the exciton luminescence of QDs in heterogeneous structures CdSe/ZnS(thioglycolic acid)⊕ZnTMPyrP, which is complementary to the energy transfer, can be caused by the photoinduced electron transfer that involves the participation of the LUMO of the ZnTMPyrP molecule (QD* ⇒ ZnTMPyrP). [ABSTRACT FROM AUTHOR]

Three new tripyridyl tripodal ligands appended with either fullerene or pyromellitdiimide moieties, named C60-s-Tripod, C60-l-Tripod, and PI-Tripod, were synthesized and introduced into a porphyrin macroring N-(1-Zn)3 (where 1-Zn = trisporphyrinatozinc(II)). From UV-vis absorption and fluorescence titration data, the binding constants of C60-s-Tripod, C60-l-Tripod, and PI-Tripod with N-(1-Zn)3 in benzonitrile were estimated to be 3 × 108, 1 × 107, and 2 × 107 M-1, respectively. These large binding constants denote multiple interactions of the ligands to N-(1-Zn)3. The binding constants of the longer ligand (C60-l-Tripod) and the pyromellitdiimide ligand (PI-Tripod) are almost the same as those without the fullerene or pyromellitdiimide groups, indicating that they interact via three pyridyl groups to the porphyrinatozinc(II) coordination. In contrast, the larger binding constants and the almost complete fluorescence quenching in the case of the shorter ligand (C60-s-Tripod) indicate that the interaction with N-(1-Zn)3 is via two pyridyl groups to the porphyrinatozinc(II) coordination and a π-π interaction of the fullerene to the porphyrin(s). The fluorescence of N-(1-Zn)3 was quenched by up to 80% by the interaction of C60-l-Tripod. The nanosecond transient absorption spectra showed only the excited triplet peak of the fullerene on selective excitation of the macrocyclic porphyrins, indicating that energy transfer from the excited N-(1-Zn)3 group to the fullerenyl moiety occurs in the C60-l-Tripod/N-(1-Zn)3 composite. In the case of PI-Tripod, the fluorescence of N-(1-Zn)3 was quenched by 45%. It seems that the fluorescence quenching probably originates from electron transfer from the excited N-(1-Zn)3 group to the pyromellitdiimide moiety. [ABSTRACT FROM AUTHOR]

Abstract: Emission related to rare earth ions in solids takes place usually due to 4f n →4f n and 4f n−15d1→4f n internal transitions. In the case of band to band excitation the effective energy transfer from the host to optically active impurity is required. Among other processes one of the possibilities is capturing of the electron at the excited state and the hole at the ground state of impurity. The latest results on high pressure investigations of luminescence related to Pr3+ and Eu2+ in different lattices are briefly reviewed. The influence of pressure on anomalous luminescence and 4f n−15d1→4f n luminescence in BaSrF2:Eu2+ and LiBaF3:Eu2+ systems and Pr3+ 4f n →4f n emission quenching is presented and discussed. A theoretical model describing the impurity-trapped exciton as a system where a hole is localized at the impurity and an electron is captured by Coulomb potential at Rydberg-like states is developed. The results show the importance of local lattice relaxation for the creation of stable impurity-trapped exciton states. The ligands shifts create a potential barrier that controls the effect of mixing between the Rydberg-like electron and localized electron wave functions. [Copyright &y& Elsevier]

The relaxation processes that occur in ensembles of coupled silicon nanocrystals are described by a quantitative model that takes into account the energy transfer between them during exciton migration. This model is used to study the formation of singlet oxygen during the photoexcitation of silicon nanocrystals in porous silicon layers under various external conditions. It is experimentally found that, upon fine milling of as-deposited porous silicon films, the photoluminescence decay time increases despite an increase in the concentration of point defects. The photosensitized activity of ensembles of silicon nanocrystals degrades monotonically during their photostimulated oxidation. These experimental results agree completely with the conclusions of the model and are explained by a decrease in the number of exciton migration ways between nanocrystals when the granule size of a porous silicon powder decreases and by an increase in the efficiency of nonradiative recombination during the photostimulated oxidation of the nanocrystals. Our data indicate that nanocrystalline silicon is a promising material for the methods of nontoxic photodynamic therapy of oncological diseases. [ABSTRACT FROM AUTHOR]

Abstract: We analyzed the scintillation mechanism in CsCl single crystals comprising CsPbCl3-like semiconductor nanocrystals. A decay component with a subnanosecond lifetime was observed and ascribed to the exciton luminescence in the nanocrystals. This is the first observation of scintillation from semiconductor nanocrystals. In addition, slower components were observed and ascribed to the intraionic transition at isolated Pb2+ ions and the Auger-free luminescence in the CsCl matrix. Furthermore, it was shown that the nanocrystals absorbed and re-emitted the scintillation photons from the isolated Pb2+ ions. The results in this report clearly indicates that the semiconductor nanocrystals function as ultrafast “luminescent centers,” and complicated scintillation dynamics are observed due to the luminescence from different components in the crystal and the radiative energy transfer between them. [Copyright &y& Elsevier]

Abstract: We studied fast luminescence of barium, calcium and strontium fluoride crystals in the excitonic emission region. For excitation we used high harmonics of Ti:sapphire laser generated in the rare gas cells with photon energies from 15 to 50eV. The usage of 600fs excitation pulses with 1kHz repetition rate coupled with conventional registration system allows us to measure the luminescence decay curves in the wide time domain from 50ps up to 1ms. Decay curves demonstrate the strong deviations from single and/or two-exponential decay laws. The decay curve profiles depend both on excitation and emission photon energies. We attribute the subnanosecond component to the fast dissociation of exciton to the F–H pair at 300K. The energy transfer from exciton to the F-center or another exciton also contributes to the non-exponential decay. [Copyright &y& Elsevier]

Spectral properties, energy structure, and electronic processes in DNA, poly(dAdT)2, d(CCCGGGTTTAAA), d(ATC), d(AT), dGMP, dAMP, dCMP, dTMP were studied. The DNA lowest excited electronic singlet and triplet levels are connected with guanine and adenine bases, correspondingly. The DNA fluorescence is close to a linear combination of the guanine and cytidine emissions and connected, to a greater extent, with the singlet energy transfer to these bases. The origin of the DNA phosphorescence is associated with AT-sequences that are traps of triplet excitations in DNA. The triplet energy transfer to these centers and adenine bases (that are most photostable) leads to the DNA self-protection against a damage induced by electronic excitations of DNA. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the optical properties of polymeric blend poly(3-thiophene acetic acid)–poly(vinyl alcohol). We have observed two band sets with different features in the photoluminescence spectrum. One set shows a band peak at 560nm and the other shows two band peaks at 670 and 710nm. We have analyzed the polarization and temperature dependence of photoluminescence spectrum. We have observed that the first set is unpolarized and shows weak temperature dependence, while the second one shows strong temperature dependence and a polarized band at 710nm. These results were interpreted as evidence of energy transfer associated with migration and trapping of excitons in the poly(3-thiophene acetic acid) chains using a kinetic model with we estimated the energy of the trap site for the triplet exciton emissions. [Copyright &y& Elsevier]

Abstract: Ortho-phthalic anhydride was modified with long chain alcohol (1-hexadecanol, 1-octadecanol and 1-eicosanol) to their corresponding mono-L phthalate (L=hexadecyl, octadecyl and eicosyl), i.e. monohexadecyl phthalate (16-Phth), monooctadecyl phthalate (18-Phth), and monoeicosyl phthalate (20-Phth), respectively. Nine novel lanthanide (Eu3+, Tb3+ and Dy3+) complexes with these three mono-L phthalate ligands were synthesized and characterized by elemental analysis and IR spectra. The photophysical properties of these complexes were studied in detail with various spectroscopes such as ultraviolet–visible absorption spectra, low temperature phosphorescence spectra and fluorescent spectra. The ultraviolet–visible absorption spectra show some band shifts with the different chain-length of phthalate monoester and homologous lanthanide complexes. From the low temperature phosphorescent emission, the triplet state energies for these three ligands were determined to be around 22,650cm−1 (16-Phth), 23,095cm−1 (18-Phth) and 22,400cm−1 (20-Phth), respectively, suggesting they are suitable for the sensitization of the luminescence of Eu3+, Tb3+ and Dy3+. The fluorescence excitation and emission spectra for these lanthanides complexes of the three ligands take agreement with the above predict from energy match. [Copyright &y& Elsevier]

In this paper, the upconversion luminescence of Er3+ ion-doped and Er3+/Tm3+ ion-codoped 70GeS2–10In2S3–20CsBr chalcohalide glasses were studied with 808 or 980nm laser diode as an excitation source. Results show that both excitations induced intensive green upconversion emissions for Er3+ ion-doped samples, which were greatly enhanced by Tm3+ ions codoping with an 808 nm laser source but became weakened under 980 nm excitation. The possible mechanisms involved under the different pump schemes are discussed in view of the energy transfer processes existing in the Er3+/Tm3+ ion-codoped glasses. [ABSTRACT FROM AUTHOR]

Single-phased Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ phosphors were synthesized by solid-state reaction method. The X-ray powder diffraction (XRD), photoluminescence (PL) spectrum and energy transfer from Ce3+ to Mn2+ of the samples were investigated. The PL spectrum of Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ show there is a wide hump in the range of 300 to 450 nm of Ce3+ ions and characteristic peak of Mn2+ ions. The emission intensity of Mn2+ increased and that of Ce3+ decreased with increasing Mn2+ concentration. The color-tunable of the Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ phosphors adjust from blue to yellow by changing the Mn2+ doping concentration. The decay curves show that energy transfer mechanism between Ce3+ and Mn2+ is quadrupole-quadrupole interaction. Moreover, the Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ phosphors exhibit excellent thermal stability. Based on obtained results, the Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ phosphors can act as efficient candidate phosphors materials for NUV-pumped white light-emitting diodes. [ABSTRACT FROM AUTHOR]