Search

Double perovskite Ca 3 LiSbO 6 : x %Mn4+, y %Eu3+ far-red emitting phosphors with zero-thermal quenching properties as well as the sensitization effect of Eu3+ ions were reported. The Ca 3 LiSbO 6 :0.4%Mn4+ phosphor showed an emission intensity of 109 % at 423 K compared with that at 298 K. In addition, the emission intensity of Ca 3 LiSbO 6 :0.8%Mn4+, 4%Eu3+samples can be enhanced to about 1.25 times that of Ca 3 LiSbO 6 :0.4%Mn4+ due to the sensitization of Eu3+ ions. Meanwhile, the Ca 3 LiSbO 6 :0.8%Mn4+, 4%Eu3+ phosphor showed an internal quantum efficiency (IQE) of 78.9 % as compared with that of Ca 3 LiSbO 6 :0.4%Mn4+ (60.7 %), and the external quantum efficiency (EQE) also enhanced from 52.8 % to 68.5 % at the same time. Under the excitation of 365 nm light, the Ca 3 LiSbO 6 : x %Mn4+, y %Eu3+ samples display an emission peak at 698 nm, which is appropriate for the absorption of plant pigments including chlorophyll a , b and phytochrome of PFR. The result indicates that the Ca 3 LiSbO 6 : x %Mn4+, y %Eu3+ phosphors may have a potential in the application fields of pc-LEDs and indoor plant cultivations. [Display omitted] • Energy transfer process from Eu3+ to Mn4+ was observed in Ca 3 LiSbO 6 host. • Sensitization of Eu3+ ions results in a high IQE of 78.9 % for CLSO:0.8%Mn4+, 4%Eu3+ phosphor. • The CLSO:0.4%Mn4+ phosphor showed a zero thermal quenching performance with 109 % PL intensity maintained at 423 K. [ABSTRACT FROM AUTHOR]

Location of lanthanide levels in the bandgap, vacuum referred binding energy (VRBE) in the lanthanide ground state and energy of lanthanide charge transition levels (CTLs) are just three different namings for the same concept. A concept of importance for the performance of lanthanide activated compounds. Energy differences of CTLs with the conduction band bottom and valence band top are important when it concerns e.g. lanthanide luminescence, charge carrier trapping, and valence stability. Effect of temperature on CTL energy or VRBE has so far never been addressed despite that luminescence application and thermoluminescence studies may span a temperature range from 10 K to 1000 K. In this work information on the bandgap (or energy of host exciton creation) around 10 K and at RT in compounds is gathered to demonstrate that bandgap decreases by 0.1 eV to 0.3 eV when temperature increases to RT. A similar decrease will be demonstrated for the energy of electron transfer from the VB to a trivalent lanthanide. The findings have consequences for VRBE-diagram construction, i.e. the experimental parameters for such construction should all apply to the same temperature. They also have consequences on how to relate luminescence thermal quenching energy barriers and TL derived electron and hole trap depths with a VRBE diagram. By proper evaluating the effects of temperature, accuracy of VRBE diagrams and consistency with luminescence and thermoluminescence data can be improved. • Data has been collected on temperature dependence of bandgap and Eu charge transfer band energies. • The effect on VRBE schemes, lanthanide trap depths and quenching temperature has been explored. • Lanthanide and conduction band levels move down and anion levels move up with temperature. [ABSTRACT FROM AUTHOR]

The photoluminescence of terbium(III) chloride in liquid ammonia at 293 K and 8.8 atm is considered. The solubility of TbCl 3 crystal hydrate in ammonia is 5∙10−4 mol/L. The luminescence spectrum of the solvated Tb3+ ion in this solution coincides with the luminescence spectrum of the hydrated Tb3+ ion in a similar aqueous solution at atmospheric pressure. The measured excited state (5D 4) lifetime τ of the terbium ion is somewhat longer in ammonia (470 μs) than in water (420 μs). The (Tb3+)* luminescence in ammonia is quenched by solvated electron (e s –), formed upon dissolution of lithium metal. Under these conditions, a solution of Tb3+ and e s – is unstable, precipitate is being formed, and continuous change in the component concentrations takes place. This hampers obtaining an adequate Stern-Volmer dependence of the Tb3+ luminescence intensity on the concentration of the quencher e s –, which is determined by measuring the absorbance of the solution at 1400 nm at the absorption band of e s –. A linear dependence was obtained by measurement of terbium ion τ with variable e s – concentration. The results were used to calculate the bimolecular rate constant k = (3.2 ± 0.3)∙108 M−1s−1 for the assumed quenching reaction (Tb3+)* + e s – → Tb2+. [Display omitted] • The Tb3+ ion photoluminescence was recorded in liquid NH 3 • The e s −, generated by dissolving Li in NH 3 , quenches Tb3+ photoluminescence • The quenching occurs via (Tb3+)* + e s –.→ Tb2+ reaction • The quenching reaction rate constant was found from (Tb3+)* lifetime dependence on [e s −] [ABSTRACT FROM AUTHOR]

This study presents a comprehensive investigation into the structural and luminescent properties of lanthanide 2-hydroxybenzoate compounds, focusing on Eu3+ and Tb3+ ions in both single and mixed systems. The X-ray structures of (Hphen) 2 [Eu 2 (2-OHBz) 8 (H 2 O) 2 ]·2H 2 O (1a ·2H 2 O) and [Eu(2-OHBz) 3 (phen) 2 ]·PhMe (2a ·PhMe) were determined, where 2-OHBz: 2-hydroxybenzoate and phen: 1,10-phenantroline, revealing triclinic crystal structures with distinct coordination geometries. Compound 1a ·2H 2 O displayed a centrosymmetric dinuclear anion with a coordination number of eight for each Eu3+ center, while compound 2a ·PhMe exhibited a neutral mononuclear complex with a decacoordinated Eu3+ center. A comparative analysis of luminescent properties between these compounds unveiled significant differences in the nonradiative decay rates of the 5D 0 level of Eu3+ ions, suggesting potential luminescence-quenching channels. The investigation is extended to mixed Eu3+-Tb3+ systems, demonstrating efficient Tb3+ to Eu3+ energy transfer, especially at room temperature. Three models, including two novel ones proposed in this study, were considered to rationalize energy transfer in the mixed systems. Our theoretical-experimental investigation reveals that variations in lifetimes of the emitting level 5D 0 of Eu-2-OHBz mononuclear and binuclear complexes, or mixed Eu/Tb-2-OHBz complexes, with 1,10-phenanthrolines, primarily result from multiphonon decay processes; however, low-energy ligand-to-metal charge transfer (LMCT) states play a key role in suppressing luminescence in the binuclear complex compare to the mononuclear ones. The image depicts X-ray structures of (Hphen) 2 [Eu 2 (2-OHBz) 8 (H 2 O) 2 ]·2H 2 O (1a) and [Eu(2-OHBz) 3 (phen) 2 ]·PhMe (2a), sample photos with UV illumination, energy transfer processes, and a luminescence decay curve modeled with three different approaches. These models are used to rationalize the luminescent properties of mononuclear and binuclear Eu/Tb-2-hydroxybenzoate complexes with 1,10-phenanthroline. [Display omitted] • Structural and luminescent properties of the mono and binuclear Eu/Tb-2-hydroxybenzoate complexes with 1,10-phenanthroline. • Luminescence activation and quenching of Eu3+ ions in mixed systems. • Novel models for understanding energy transfer and excited-state lifetimes in mixed lanthanide systems. [ABSTRACT FROM AUTHOR]

In this paper, we performed a comparative spectroscopic analysis of Tm3+-doped glasses based on GeO 2 -BaO-Ga 2 O 3 (GBG) and TiO 2 -GeO 2 -BaO-Ga 2 O 3 (TGBG) to achieve broadband luminescence at 1.8 μm. Glasses were prepared at different doping concentrations (0.05 mol% and 1mol%) in order to investigate the effect of Tm3+ ions as well as host composition (GeO 2 :TiO 2 molar ratios) on near-IR luminescence properties. We report on the hypersensitivity of the transition 3H 6 → 3F 4 of Tm3+ in a series of titanate-germanate glasses, which was shifted to longer wavelengths with increasing TiO 2 concentration. The relative intensity of the main near-IR emission band corresponding to the 3F 4 → 3H 6 (1.8 μm) transition of Tm3+ was 4.8-fold enhanced for glass with molar ratio GeO 2 :TiO 2 = 1:5 compared to GBG glass system. We observed the luminescence quenching phenomena for samples containing more than 0.5 mol% of Tm3+ ions. The calculated spectroscopic parameters, such as measured luminescence lifetime (τ m) and the quantum efficiency (η), were discussed and compared to the different laser glasses. Importantly, luminescence decay curves have been examined using the Inokuti-Hirayama model. Additionally, the correlation between optical properties and local structure in glasses was well evidenced by Raman spectroscopy. The proposed strategy, in combination with various chemical composition of glass host activated by various Tm 2 O 3 concentration, might be beneficial for modern near-infrared photonics. • NIR emission of Tm3+ in BGG glass was examined with TiO 2 and activator content. • The main band due to 3F 4.→ 3H 6 transition of Tm3+ was 4.8-fold enhanced. • The hypersensitive 3H 6.→ 3F 4 transition of Tm3+ was shifted to longer wavelengths. • The luminescence decay curves were examined by the Inokuti-Hirayama model. • Tm3+-doped glasses with GeO 2 :TiO 2 = 1:1, 1:2, 1:3 can be attractive for photonics. [ABSTRACT FROM AUTHOR]

Ceramic samples of two multi-cation fluoride compositions, namely Na 3 CaMg 3 AlF 14 doped with Ce3+ or Eu2+ and KCaAl 2 F 9 doped with Eu2+, have been synthesized using a conventional solid-state reaction method. The XRD analysis shows that the new polymorphic modification of Na 3 CaMg 3 AlF 14 with the cubic A 2 B 2 X 7 pyrochlore crystal structure (space group Fd 3 ‾ m , lattice parameter 10.172 Å) has been obtained. This conclusion is confirmed with the simulation of the XRD pattern for the cubic pyrochlore structure by introducing random occupation of Na+ and Ca2+ ions at the A-type sites as well as Mg2+ and Al3+ ions at the B-type sites in the structure of rhombohedral Na 3 CaMg 3 AlF 14. It has been shown that doping of the Na 3 CaMg 3 AlF 14 pyrochlore matrix with Ce3+ ions creates several Ce3+ optical centers with different spectral and decay properties of 5d-4f luminescence. In contrast to that, doping with Eu2+ ions creates a single optical center by the substitution for the Na/Ca A-type site in the cubic Na 3 CaMg 3 AlF 14 pyrochlore structure. In Eu2+-doped Na 3 CaMg 3 AlF 14 , the Eu2+ emission band caused by the interconfigurational 4f65d – 4f7 transition has a rather narrow width (FWHM = 29 nm) which is considerably less than that observed in Eu2+-doped KCaAl 2 F 9 (FWHM = 44 nm) in which the emission band is broadened due to the existence of two types of sites for doping Eu2+ ions. The Eu2+ ions doped into Na 3 CaMg 3 AlF 14 and KCaAl 2 F 9 hosts emit not only broad-band 4f65d – 4f7 luminescence but also a narrow-line 4f7 – 4f7 (6P 7/2 - 8S 7/2) emission which is not observed under excitation to the lowest-energy 4f65d state. It has been shown that both Na 3 CaMg 3 AlF 14 :Eu2+ and KCaAl 2 F 9 :Eu2+ demonstrate a rather good thermal stability of luminescence with thermal quenching temperature T 1/2 equal to 504 and 573 K, respectively. • Novel cubic polymorphic modification of Na 3 CaMg 3 AlF 14 pyrochlore has been synthesized. • Eu2+ ions create a single luminescence center in the cubic Na 3 CaMg 3 AlF 14 pyrochlore. • In the Na 3 CaMg 3 AlF 14 host Eu2+ ions show both 4f65d-4f7 and 6P 7/2 -8S 7/2 luminescence. • 4f65d-4f7 luminescence of Eu2+ doped into Na 3 CaMg 3 AlF 14 has high thermal stability. • Ce3+ ions create several luminescence centers in the cubic Na 3 CaMg 3 AlF 14 structure. [ABSTRACT FROM AUTHOR]

A set of single-phase Cd 1- x Zn x WO 4 (x = 0–1) solid solutions synthesized by spontaneous crystallization technique was studied by the methods of luminescence and electron paramagnetic resonance (EPR) spectroscopy. Luminescence spectra of all studied solutions are characterised by a single emission band related to the intrinsic emission of self-trapped excitons. The dependence of luminescence spectra and thermostimulated luminescence (TSL) curves on solution composition was investigated, and the origin of TSL peaks was analysed on the basis of the EPR data. It is shown that the values of optical bandgap and activation energy of luminescence thermal quenching gradually change with solution composition. Several phenomena are observed in solid solutions predominantly at intermediate concentrations of Cd and Zn cations that can be connected with the structural disorder of the solid solutions. In particular, the deviation of lattice parameters from the Vegard's law, the redshift and broadening of the emission band, the suppression of low-temperature (T < 80 K) TSL peaks related to self-trapped holes and the broadening of high-temperature (100–200 K) TSL peaks related to structural defects. The structural disorder arises due to the non-homogeneous distribution of substitutional atoms in cation lattice sites, pronounced because of the mismatch in ionic radii of substitutional cations, which reaches 28.3 % for Cd2+ and Zn2+. • Single-phase Cd 1- x Zn x WO 4 solutions were grown by spontaneous crystallization method. • Crystal structure disorder is manifested in luminescence spectra and TSL curves. • Defect origin is determined using EPR spectroscopy. • Hole self-trapping is suppressed in solid solutions due to structural disorder. [ABSTRACT FROM AUTHOR]

The study aim is to establish the effect of various interface passivators (thiocarboxylic acids: thioglycolic acid (TGA), 2-mercaptopropionic acid (2-MPA), 3-mercaptopropionic acid (3- MPA); amorphous SiO 2 shell) on the thermally stimulated luminescence of PbS quantum dots (QDs) with close value of the average nanocrystals size, which are equal to 3.0 ± 0.5 nm. All samples of PbS QDs, passivated with thiocarboxylic acids are characterized by exciton luminescence at 1120 nm and trap state luminescence in the region of 1200–1300 nm. The formation of PbS/SiO 2 core/shell QDs leads to the trap state luminescence quenching in the region of 1200–1300 nm. Two types of shallow traps with a depth of 0.17 eV and 0.25 eV were found for PbS QDs, using the thermally stimulated luminescence technique in the temperature range from 80 K to 350 K. The formation of PbS/SiO 2 core/shell QDs leads to a decrease in the concentration of traps with a depth of 0.25 eV, which indicates their interface nature. The obtained results indicate that the increase in the quantum yield of exciton luminescence at 1120 nm and of trap state luminescence quenching in the region of 1200–1300 nm during the formation of PbS/SiO 2 core/shell QDs is the result of defects passivation with two types. • The effect of various interface passivators on the thermally stimulated luminescence of PbS quantum dots (QDs) with close value of the average nanocrystals size was studied. • Two types of shallow traps with a depth of 0.17 eV and 0.25 eV were found for PbS QDs, using the thermally stimulated luminescence technique in the temperature range from 80 K to 350 K. • The formation of PbS/SiO 2 core/shell QDs leads to a decrease in the concentration of traps with a depth of 0.25 eV, which indicates their interface nature. [ABSTRACT FROM AUTHOR]

The Monte Carlo method was used to calculate static dipole-dipole (Förster) quenching of manganese luminescence in nanoparticles of various sizes in the semi-magnetic semiconductor Zn 0.99 Mn 0.01 S. For the first time, the quenching is stated to play insignificant role in sub-nanosecond huge drop of the emission transient. Parameter values of Förster's quenching stage of luminescence transient – characteristic quenching distance, concentration of quenchers, average quenching rate, probability of quencher absence in a nanoparticle, quenching amplitude, etc. − were found from a comparison of calculations with experimental transients. The values are dependent on nanoparticle growth technology. Calculations show that luminescence efficiency increases with a decrease in actual size of nanoparticles, while probability of obtaining nanoparticles without quenchers asymptotically approaches unity at smaller size. The latter condition together with agglomeration absence and greater intrinsic time decay are the main conditions for higher efficiency of manganese luminescence in ZnS:Mn2+ nanoparticles. The analysis of previous researches and our experiments showed that the most fast transient component originated from ZnS host. • Conditions of high efficiency of manganese luminescence are formulated anew in nanoparticles of Zn:Mn2+. • Monte Carlo model is worked out to calculate parameters of Förster's quenching in a nanoparticle. • Mn2+-quencher interaction strength (anew) and mean rate of the quenching are calculated for the first time. • For the first time, it is shown insignificant role of Förster's quenching within sub-nanosecond time span of the luminescence transient. • The transient sub-nanosecond component is highly probable of ZnS host nature. [ABSTRACT FROM AUTHOR]

In this work, trivalent dysprosium was incorporated with lithium yttrium phosphate LiY 5 P 2 O 13 (LYP), obtaining a yellow-emitting material. The crystallographic sites of introduced Dy3+ activators are determined through the comprehensive analysis of the XRD investigation, DFT computation, and experimental luminescence spectra. Under 353 nm excitation, the LYP:Dy3+ phosphor shows bright yellow emission owing to dominant 4F 9/2 → 6H 13/2 transition (577 nm) of Dy3+. The luminescence quenching occurs when the Dy3+ content exceeds 0.07 mol, originating from the dipole–dipole interaction. Furthermore, the excellent thermal stability behavior (84 % at 423 K) and good resistance to color shifting (0.00634 at 473 K) for title phosphor are manifested by temperature-dependent investigation. Eventually, the w-LED fabricated with LYP:0.07Dy3+ and commercial materials exhibits stable white-emitting output (0.3595, 0.3179) with high R a (85) and low CCT (4203 K). All the study demonstrates that the LYP:Dy3+ material is a perspective candidate in solid-state illustration field. [Display omitted] • The site-selective occupancy of Dy3+ was confirmed via the combination of theoretical and experimental methods. • LiY 5 P 2 O 13 :Dy3+ exhibits excellently thermostable luminescence and good chromaticity shift resistance. • The w-LED with R a = 85 and CCT = 4203 K was assembled. [ABSTRACT FROM AUTHOR]

Optical thermometers based on the luminescence of trivalent rare earth-doped materials are often explored due to their high sensitivity and performance in the visible and infrared spectral regions. Among them, Nd3+ ions are widely used because they operate efficiently in the main biological windows, although an increase in their sensitivity at low temperatures is still desired. This work aims to investigate the influence of the addition of silver nanoparticles (Ag-NPs) on the temperature-dependent luminescence of Nd3+ doped TeO 2 –ZnO glasses over wide temperature ranges (295–480 K). The study shows that the plasmonic effects induced by Ag-NPs lead to an absolute sensitivity increase of up to ∼28.6% in Nd3+-based thermometers operating through a set of three thermally coupled energy levels. In addition, thermometry studies using high-power excitation beams reveal that the thermo-optical properties of Ag-NPs favor optical thermometer sensitivity enhancement due to local heating effects and compensates for the losses caused by luminescence quenching at high concentration of Nd3+ ions. Moreover, an experiment analyzing the speckle patterns generated by Nd3+ doped TeO 2 –ZnO glasses, conducted for the first time to the best of our knowledge, confirms the influence of the thermo-optical effects of Ag-NPs in optimizing the sensitivity of optical thermometers. • Metal NPs are a key piece to optimize the RE-based optical thermometer sensitivity. • Metal NPs consolidate Nd3+-doped TZO glasses as materials for optical thermometers. • Thermo-optical properties of metal NPs can compensate for luminescence quenching. • Speckle patterns are tools to study the thermo-optic effects of RE-doped glasses. [ABSTRACT FROM AUTHOR]

Perovskite, particularly halide perovskite shows tremendous application in the field of optoelectronic devices such as Light emitting diode (LED) and solar cells. Semiconducting nanomaterials like perovskite nanomaterials have photoactive components and are used as electron as well as hole donors. A hybrid combination of organic acceptors such as Anthraquinone (AQ) and Tetracyanoquinodimethane (TCNQ) with CsPbX 3 (X = Cl, Br, I) perovskite nanomaterials at the interface is a unique path for charge separation. The surface of the perovskite nanomaterial plays an important role in the electron-hole charge separation. The surface of the perovskite nanomaterial is responsible for the interaction between this redox couple. Only those molecules show better charge separation which interacts more efficiently with the excited state of the perovskite nanocrystals (PNCs), but very few organic molecules show this kind of redox properties. In the present study, we employed AQ and TCNQ to extract charges from PNCs. We performed photoluminescence (PL) and time-correlated single photon count spectroscopy (TCSPC) to investigate the impacts of both organic acceptor molecules on the lifetime and photoluminescence (PL) of PNCs. PNCs possessed distinct lifetime and luminous characteristics prior to and after the incorporation of quenchers, however, in the case of TCNQ, improved charge separation occurred, as evidenced by PL and TCSPC. We additionally employed SEM (scanning electron microscopy) and TEM (transmission electron microscopy) to investigate the influence of the quencher on morphology. [Display omitted] • CsPbBr 3 perovskite nanocrystals are synthesized using Ligand assisted reprecipitation technique. • Anthraquinone and tetracyanoquinodimethane is used as emission quencher. • Efficient luminescence quenching is observed and characterized by various techniques. • Morphological analysis of the pristine nanocrystals and the composite nanocrystals are also performed. [ABSTRACT FROM AUTHOR]

Highly luminescent red emitting Zn2+ modified Gd 2 O 3 :Eu3+, Li + nanophosphors with superior colour purity were prepared by the organic mediated solvothermal combustion of metal-citrates in diethylene glycol. Structure, morphology, spectroscopic and luminescence dynamics of the nanophosphors were found to be sensitive to Zn2+ concentration. Simultaneous incorporation by Zn2+ and Li+ ions in Gd 2 O 3 :Eu3+ resulted in better emission features and improved photophysical radiative properties. Enhanced photoemission has resulted from the cooperative and combined roles caused by Li+ and Zn2+ ions, improvement of crystallinity, modifications of the crystal field and reduced symmetry around Eu3+ ions in Gd 2 O 3. Photoemission intensity of the optimal zinc compensated phosphor with composition Gd 1.71 Eu 0.1 Li 0.15 Zn 0.04 O 3 was found to be 1.82 times that of Gd 1.75 Eu 0.1 Li 0.15 O 3 and it exhibited a lifetime of 1.467 ms with the highest colour purity of 97.06 %. Luminescence decay profiles of all the synthesized phosphors were found to follow single exponential behaviour. Judd-Ofelt analysis revealed that the emission intensity parameters were found to be optimum for Gd 1.71 Eu 0.1 Li 0.15 Zn 0.04 O 3 phosphor, indicating the highest asymmetry of local environment around Eu3+ ions in this material. Better radiative and Judd-Ofelt intensity parameters obtained indicate that this highly luminescent red emitting phosphor can act as a promising material for high resolution phosphor coated displays, deep UV excited phosphor converted LEDs and for developing defence security inks. [Display omitted] •Zn2+ modified Gd 2 O 3 : Eu3+, Li + red nanophosphors have been synthesized by a novel organic mediated solvothermal method. •Zn2+ in Gd 2 O 3 : Eu3+, Li+ promoted the grain growth, crystallinity and altered the structural symmetry around Eu3+ ions. •Emission intensity of Gd 1.71 Eu 0.1 Li 0.15 Zn 0.04 O 3 (Lifetime: 1.467 ms, colour purity: 97.06%) was 1.82 times that of Gd 1.75 Eu 0.1 Li 0.15 O 3. •Photometric and radiative parameters were evaluated by Judd-Ofelt theory and discussed the results in detail. •Zn2+ modified Gd 2 O 3 : Eu3+, Li+ nanophosphors may act as a potential red phosphor in functional photonics. [ABSTRACT FROM AUTHOR]

The fluorophosphate glasses with composition of Ba(PO 3) 2 – AlF 3 –CaF 2 – MgF 2 –BaF 2 – SrF 2 –YbF 3 – ErF 3 were synthesized and their spectroscopic properties were studied. The main attention here was paid to studying the luminescence kinetics Yb3+ (1040 nm) and Er3+ (1550 nm, 655 nm and 540 nm). It has been found that the population of the 4I 13/2 (Er3+) level and the relaxation of the 2F 5/2 (Yb3+), 4F 9/2 , and 2H 11/2 +4S 3/2 (Er3+) levels are close to exponential and the probabilities of these processes are well approximated by linear functions with respect to the ytterbium concentration. All this led to the conclusion that the migration-accelerated energy transfer makes a significant contribution to the population and deactivation of these energy levels. A scheme of the main energy transfer channels in an ensemble of ytterbium and erbium ions and the corresponding system of rate equations are proposed. On the basis of these equations, mathematical modeling of the luminescence kinetics of ytterbium and erbium ions was carried out and the energy transfer parameters were estimated. • Er3+ and Yb3+ doped fluorophosphate glasses spectroscopic properties were studied. • Mathematical modeling of the luminescence kinetics of Er3+ and Yb3 was carried out. • Energy transfer parameters between Er3+ and Yb3 were estimated. [ABSTRACT FROM AUTHOR]

This study has demonstrated a salient negative thermal quenching behavior of upconversion (UC) luminescence in YAG:Yb/Er transparent ceramic phosphor in a wide temperature range from 100 to 500 K. With the rise of temperature, UC luminescence deteriorates under the excitation at λ ex = 932 nm, whereas it intensifies remarkably at λ ex = 974 nm (i.e., the integrated emission intensity increased by nearly 30 folds from T = 100 K to T = 500 K), indicating a dynamic UC luminescence-temperature relation dependent upon the incident excitation energy. Our later photophysical analysis shows that the negative thermal quenching behavior was mainly ascribed to a phonon-assisted thermal excitation process which occurs at low excitation energy. More interestingly, it is found that despite a final decline at high temperature, the UC luminescence lifetime increases as the temperature rises before certain degrees. A modified equation for luminescence lifetime was proposed and used for our interpretation. This work not only demonstrates large negative thermal quenching of UC luminescence in the ceramic phosphor for the first time, but also provides a deep insight into the photophysical behavior of UC luminescence. • A large-negative thermal quenching of UCL has been achieved from 100 to 500 K. • A solid explanation with thermal excitation was proposed for our observation. • Luminescence lifetime increases at low temperature with the excitation at 974 nm. • A modified expression was deduced for luminescence dynamics at low temperature. [ABSTRACT FROM AUTHOR]

Spectra of steady-state X-ray excited luminescence (XEL) and thermally stimulated luminescence (TSL) of CsPbBr 3 single crystals in the temperature range of 80–294 K were studied. Each of the measured XEL spectra of CsPbBr 3 single crystal contain only one elementary band peaking at 535 nm, which can be attributed to the radiative decay of the matrix exciton. The activation energy of exponential luminescence thermal quenching in this range, as determined by Mott's formula, is equal to 75 meV, close to the hole trap depth of 110 meV obtained for the main TSL peak of this crystal at 125 K. This value of the XEL quenching activation energy is associated with the thermal deactivation of the exciton hole component in the CsPbBr 3 matrix. Doping of KBr crystals with CsPbBr 3 perovskite impurities (0.05–1 mol. %) leads to the formation of CsPbBr 3 micro- and nanocrystals in a KBr matrix with characteristic spectra of exciton photo- and XEL luminescence. A five-fold increase in the intensity of XEL was registered in KBr: CsPbBr 3 (0.05 mol. %) samples at 294 K compared to that of CsPbBr 3 single crystal. The temperature dependence of the XEL intensity of KBr: CsPbBr 3 crystals and the analysis of their TSL integral curves allow us to make a conclusion about the hole mechanism of high-energy excitation energy transfer from the matrix to the activator resulting in the appearance of typical exciton luminescence in CsPbBr 3 nanoparticles. • A five-fold increase in the intensity of XEL was registered in KBr: CsPbBr 3 (0.05 mol. %) crystal at 294 K. [ABSTRACT FROM AUTHOR]

ZnO nanoparticles (NPs) doped with iron were synthesized by the microwave-hydrothermal method using various reagents. The properties of these NPs were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL), cathodoluminescence (CL) measurements. In the article, we discuss the surprising results of optical studies of ZnO:Fe NPs. The phenomenon of luminescence quenching by the magnetic ion, characteristic for bulk materials, was not observed. We examined three potential reasons for this observation. • ZnO:Fe nanoparticles were synthesized by microwave hydrothermal method using various reagents. • no quenching of luminescence by iron ions in ZnO was found. • XRD, SEM, EDX, PL, CL, XPS measurements were carried out and Mӧssbauer spectra were recorded. [ABSTRACT FROM AUTHOR]

Two 1-D lanthanide-based CPs (coordination polymers), Eu-CP and Tb-CP , have been solventhermally synthesized from a phenolic-linked tricarboxylate ligand 1,3,5-tri(2-carboxyphenoxy)benzene (H 3 L). Both complexes demonstrate stability and strong characteristic luminescence emissions in organic and water media. They also possess excellent luminescence sensing activities toward Fe3+ and Cr 2 O 7 2−/CrO 4 2− in DMF and aqueous solutions as well as simulated biological system. Notably, Tb-CP is one of the very few examples to effectively distinguish between CrO 4 2− and Cr 2 O 7 2− in aqueous and HEPES media. Both CPs could be simply and quickly regenerated at least five circles. The research on sensing mechanism indicated that the luminescence quenching may be related with the energy competition and weak interactions between CPs and sensing analytes. Image 1 [ABSTRACT FROM AUTHOR]

Tb3+/Dy3+ co-doped Y 6 Si 3 O 9 N 4 :Ce3+ oxynitride phosphors were prepared in this work. The properties of the prepared phosphors, e.g. X-ray diffraction (XRD), photoluminescence (PL) spectra, lifetime and thermal-dependent luminescence quenching were investigated systematically. Under near-UV excitation, co-doped Tb3+ and Dy3+ into Y 6 Si 3 O 9 N 4 :Ce3+ phosphor generated a narrow green line peaked at 550 nm and a yellow line peaked at 575 nm, respectively. Energy is efficiently transferred from Ce3+ to Dy3+ and Tb3+ ions according to the study results. Fluorescence decay patterns are studied as a function of Tb3+ and Dy3+ concentrations. For the new synthesized phosphors, their temperature-dependent photoluminescence properties were investigated, which demonstrates that the emission intensity at 150 ○C reduced from 100% to 32.0% measured at 30○C. Commission on illumination value of color tumble emission is also discussed in detail. This work verifies the suitable application of the new oxynitride phosphor in the LEDs. We introduce a Tb3+/Dy3+ co-doped oxynitride Y 6 Si 3 O 9 N 4 :Ce3+ phosphor for near-UV LEDs. Image 1 [ABSTRACT FROM AUTHOR]

Eu3+-, Er3+-doped and Er3+/Yb3+-codoped niobium alkali germanate glasses, in the compositional host system GeO 2 -Nb 2 O 5 -K 2 O were synthesized by the conventional melt-quenching technique. Glass-ceramics were manufactured by controlled heat treatment of the precursor glasses. Homogeneous glasses and nanocrystalline glass-ceramics were investigated by DSC, XRD, TEM and spectroscopic analysis. K 2 Nb 14 O 36 crystals are formed in the prepared glass-ceramics. This crystalline phase has low phonon energy as compared to the precursor glass and a variety of chemical sites for rare-earth ions. In glass-ceramics, the rare-earth ions occupy higher symmetry sites of the K 2 Nb 14 O 36 nanocrystals resulting in inhomogeneous broadband emissions. Judd-Ofelt parameters were obtained for the Eu3+- and Er3+-doped samples. Glass-ceramics heat-treated for 20 h exhibited the highest photoluminescence quantum efficiency. The increased quantum efficiency is due to the decrease of nonradiative decay processes, that depopulate the excited levels, as well as the decrease in hydroxyl content and overall phonon energy. However, luminescence quenching is verified for samples with longer crystallization times, which emphasizes the importance of optimized heat treatment parameters. The gain coefficient and upconversion data were obtained and corroborate the potential application of these materials as photonic devices, such as visible and NIR laser and optical amplifiers. Image 1 [ABSTRACT FROM AUTHOR]

In the present paper, we present an analysis of the luminescence decays for colloidal quantum dots (QDs) with interfaces doped with Eu3+ ions of the corresponding thenoyltrifluoroacetone complexes. The luminescence decay features related to concentration and temperature effects are considered. The Stern-Volmer plots obtained at 300 and 77 K for the trap state luminescence of CdS:Eu3+ QDs show that the QD luminescence quenching is of a dynamic character with the Stern-Volmer constant being K d y n = 3.7 ⋅ 10 5 M−1. Non-radiative excitation energy transfer from the trap state luminescence centers in CdS quantum dots to Eu3+ ions is observed. In addition, the value of the quenching rate k d y n = 2.37 ⋅ 10 13 s − 1 ⋅ M − 1 indicates that the energy transfer process has a non-diffusive nature. This conclusion is supported by the effective quenching in a frozen solution at 77 K where there is no diffusion. For CdS/TGA QDs doped with europium ions, we observe a significant increase in the luminescence lifetime (from 190 μs to 346 μs) for the band peaked at about 615 nm as compared to the free Eu:TTA complex. We conclude that Eu3+ ions are incorporated into the QD interfaces. [ABSTRACT FROM AUTHOR]

Tellurite-tungsten glasses doped with Er3+-Pr3+ were fabricated by conventional melt-quenching, increasing the Pr 2 O 3 content to enhance the emission performance and bandwidth of the 1.5 μm emission band. The spectroscopic properties in the visible and near-infrared regions are described, besides the Judd – Ofelt analysis of the Er3+. Results of the 1.5 μm emission intensity of the Er3+ under 980 nm, moreover the up-conversion emission, show an enhancement with the addition of Pr3+. Increments in the FWHM (≈ 90 nm) in the Er3+: 4I 13/2 → 4I 15/2 band are also reported, where the increment of Pr 2 O 3 content plays an important role. The analyses of the dynamics between Er3+ and Pr3+ in these glasses comprehensively explain the Er3+ emission performance in the visible and near-infrared regions for optical communications applications. • Tellurite - tungsten glasses doped with Er3+ and Pr3+ were fabricated with the melt-quenching technique and investigated. • Luminescence quenching of the emission of Er3+ was obtained due to the presence of Pr3+. • FWHM increments of the 1.5 μm emission band with the addition of Pr3+ were observed. • The dynamics between Er3+ and Pr3+ is discussed. [ABSTRACT FROM AUTHOR]

Abstract The luminescence quenching in RE3+-containing materials (RE: rare earth) has a close dependence with the water content on the first coordination sphere around the activator ions. The hydration content of [RE(TMA)] systems (TMA = 1,3,5-benzenetricarboxylic acid) is dependent on the RE3+ ionic radius, leading to elements smaller than Gd3+ to form anhydrous matrixes. It is noteworthy that [Sm(TMA)·6(H 2 O)] is hexahydrate, while [Y(TMA)] is anhydrous. In this work, we report the synthesis, characterization and the luminescent properties of [Y(TMA)] anhydrous metal organic frameworks (MOFs) serving as hosts for Sm3+ ions. The materials are synthesized by a quick and easy coprecipitation procedure in aqueous solution. Under calcination at mild conditions (starting at 500 °C, benzenecarboxylate method), the precursor complexes are converted into Y 2 O 3 :Sm3+ with strong Sm3+ photoluminescence. The compounds were characterized by different techniques (elemental analyses, infrared spectroscopy, thermogravimetry, powder X ray diffraction and photoluminescence). The phenomenological intensity parameters (Ω 2,4,6) of Sm3+ were determined by a least squares procedure based on the Judd-Ofelt theory. [ABSTRACT FROM AUTHOR]

Abstract Borophosphate glasses doped with Ag ions have been successfully prepared by melt-quenching method. Their structure and luminescence properties were analyzed by XRD, ATR-FT-IR, TEM, EDS, optical absorption, and photoluminescence measurements. The unique properties of excitation/emission of silver oxide embedded glass matrix, the inhomogeneous broadband character of B (Ag+-Ag0 pairs) and C (Ag+-Ag+ pairs) centers were identified upon 310 nm and 400 nm excitation wavelengths. Under 310 nm excitation, for heat treated samples, the B-center emission becomes narrower with an unexpected blue shift (∼463 nm), and luminescence quenching. Additionally, at 400 nm excitation (surface plasmon resonance of Ag NPs), for all samples, a broadband emission (C-center) was identified at the 450–700 nm range. The suppression of B center emission followed by an inhomogeneous broad region toward the low energy side is interpreted as due to non-radiative energy transfer process. The nanosecond decay curves were recorded at 470 nm (λ exc = 310 nm) and 550 nm (λ exc = 400 nm), respectively, and were fitted by double exponential function. The observed increase of τ 2 (longer lived decay) in HT samples is due to different size/site distribution of Ag nanoclusters/particles in glass. The evolution of τ 2 of B and C with HT is an indicative of the energy transfer from B→C and Ag NP→B→C in the studied glasses. [ABSTRACT FROM AUTHOR]

Abstract A novel near infrared long-persistent phosphor La 2 MgGeO 6 : Cr3+ was successfully prepared. Near infrared emission originates from the 2E→4A 2 transition of Cr3+ in strong crystal field. Due to the electric dipole-dipole interaction, the luminescence quenches when doping concentration of Cr3+ beyond 0.003. By co-doping Dy3+ and Sm3+, the long-persistent luminescence intensity is significantly enhanced, and the long-persistent luminescence time is also prolonged. The results of the thermoluminescence measurement show that there are two kinds of traps in La 2 MgGeO 6 :Cr3+ phosphors. The depths of two traps were calculated to be 0.796 and 1.200 eV, respectively. The co-doping of Sm3+ and Dy3+ has a great influence on deep traps and has little effect on shallow traps. The present investigation has important guiding significance for a deep understanding of the nature of traps, which has an important influence on the long-persistent luminescence of the phosphors. [ABSTRACT FROM AUTHOR]

Abstract By using tetracarboxylatoresorcin[4]arene 2,8,14,20-tetrapentyl-6,12,18,23-tetra- methoxy-4,10,16,22-tetra-carboxymethoxy-resorcin[4]arene (H 4 L), eight lanthanide-based coordination polymers (CPs), [M(HL)(DMF)(H 2 O) 2 ]·3H 2 O (M = Tb 1 , Eu 2 , Gd 3 , Yb 4 and Sm 5) and [M(HL)(DMF)(H 2 O)] (M = Ce 6 , Pr 7 and La 8), have been constructed. Isostructural CPs 1 – 5 exhibit charming ribbons built with rare earth cations and cup-like HL3− anions. The ribbons are lengthened by hydrogen bonds to constitute supramolecular layers, respectively. CPs 6 – 8 are isostructural and show unique layer networks. The luminescent properties of 1 and 2 in solid states were studied. The detection of CPs 1 and 2 towards metal cations, polyoxometalates (POMs) and organic small molecules by luminescent quenching and enhancement process has been systematically investigated. Graphical abstract Eight coordination polymers based on lanthanide ions and a tetracarboxylate-functionalized resorcin[4]arene ligand have been constructed. 1 and 2 exhibit high activities in detecting Fe3+, POMs, nitromethane and nitrobenzene by quenching effects. 2 could be employed as a turn-on-type luminescent sensor for N,N -dimethylformamide and N,N -dimethylacetamide. fx1 [ABSTRACT FROM AUTHOR]

Abstract Rod like green emitting ZnGa 2 O 4 :Tb3+ phosphor were synthesized and the effect of Tb3+ on the structural and optical properties of zinc gallate were analysed. Cubic spinel nature of ZnGa 2 O 4 :Tb3+ nano crystallite was verified from the x-ray diffraction. From the photoelectron spectroscopy analysis, chemical states of constituent elements were identified. Photoluminescence spectra reveal the green emission quenching and there are no reports about this mechanism from ZnGa 2 O 4 :Tb3+ phosphor synthesized via solid state reaction route. Quadrupole – quadrupole interaction leads to this quenching behaviour and the critical distance is 21 Å. [ABSTRACT FROM AUTHOR]

Abstract A α-Al 2 O 3 :C,Mg single crystal was investigated by means of optical absorption and photoluminescence measurements aimed at the identification of defects involved in the luminescence process. It was also investigated by thermoluminescence (TL) measurements as a function of the spectral emission in the 1.7–5.0 eV range. Radioluminescence measurements under X-ray excitation as a function of the temperature, from room temperature up to 400 °C were executed. These measurements revealed the presence of F, F-type, F-aggregate, and Mg-perturbed F-type and F-aggregate centers, and their thermal quenching behavior. Further, the role of these defects as recombination centers in the TL process was revealed. [ABSTRACT FROM AUTHOR]

The energy transfer behavior from guest organic molecules to Tb3+ activators was systematically investigated using various benzoate derivatives with high ultraviolet (UV)-harvesting ability and ready exchangeability into interlayer galleries of layered yttrium hydroxide host, Y 1·80 Tb 0·20 (OH) 5 X∙ n H 2 O (X = benzoate and its amino, hydroxy, chloro, cyano, and nitro derivatives of 2(ortho)-, 3(meta)-, and 4(para)-isomers). The difference in the interlayer arrangement of X anions depending on the types and positions of functional groups was found to be a critical factor for the energy transfer, sensitizing the luminescence of Tb3+. Despite the energy-level matching between the triplet state of X and the excited state of Tb3+, the difference in triplet state energy could not solely explain the significant change in energy transfer in the host-guest system. Instead, the interaction of X guests with host layers would be a major factor that determines the transfer of UV energy absorbed for the S 0 → S 1 transition of X to the 5D 4 excited energy level of Tb3+. In contrast, when the triplet state of X was significantly lowered by the nitro group, the inverse transfer from Tb3+ to X was followed by energy dissipation, resulting in luminescence quenching, irrespective of the difference in interlayer interaction. The effect of the types and positions of functional groups bonded to the benzene ring of benzoate on the energy absorption and transfer behavior in the host-guest system was systematically investigated using Tb3+-doped layered yttrium hydroxide. [Display omitted] • Layered rare-earth hydroxide family is an emerging class of two-dimensional host materials. • Guest benzoate derivatives were employed to sensitize the luminescence of Tb3+-doped LYH. • The positions and types of functional groups strongly affected the energy transfer to Tb3+ ions. • The luminescence of Tb3+ depended on the host-guest interaction as well as the triplet level of the guest. [ABSTRACT FROM AUTHOR]

YAlO 3 crystals doped with different concentrations (0.05, 0.1, 1.0 at.%) of Pr3+ ions were studied in this work. The crystals were grown from the melt by a micro-pulling-down (MPD) method. Luminescence and energy-storage properties of YAlO 3 :Pr crystals were studied using cathodoluminescence (CL), as well as thermoluminescence (TL) and optically stimulated luminescence (OSL). Instead of a conventional optical illumination with blue LEDs, infrared light was used for optical stimulation (IRSL). For the YAlO 3 :Pr crystals both TL glow-curves and IRSL decay curves were extensively analyzed. Both d-f transitions in UV range and f-f transitions in the visible range of Pr3+ ions were observed including radiative transitions from 3P j (j = 0,1,2) to 3F 2,3,4 and 3H 4,5,6 levels. The highest CL signal was measured for the lowest Pr3+ concentration of 0.05 mol% and a strong luminescence quenching was observed for the increase in the Pr3+ content. For the increasing dose of radiation, the intensity of the main TSL glow-peak at around 170–200 °C shows a linear behavior, regardless of the applied dopant concentration. Due to the highest TL and IRSL radio-sensitivity and stability in time after the irradiation, the YAlO 3 :Pr (0.05 mol%) perovskite seems most promising material for radiation measurement applications. • YALO 3 crystals made by micro-pulling-down technique have been investigated. • The crystals were doped with Pr3+ Rare-Earths ions. • Luminescence of Pr3+dopants was clearly observed. • Good embedded of Pr3+ions in YALO 3 matrix was confirmed. • YALO 3 with Pr3+ (0.05 mol%) was found to present the best dosimetric properties. [ABSTRACT FROM AUTHOR]

Narrow-band green-emitting phosphor plays a key role in the backlighting display field. In this work, a borophosphate phosphor RbBaBP 2 O 8 (RBBP):Tb3+ was synthesized by a solid-state reaction. Excited by 351 nm near-ultraviolet light, it displays the narrow-band green-emitting performance with the dominant 5D 4 →7F 5 transition. The green fluorescence was studied in response to the Tb3+ concentration. The quenching origin is determined. Meanwhile, the investigation of luminescence temperature quenching reveals that the phosphor possesses high thermal stability and excellent resistance to color shifting. The study suggests that the RBBP:Tb3+ phosphor would be a narrow-band green-emitting alternative for backlighting display application. [Display omitted] • A RbBaBP 2 O 8 -based phosphor activated with Tb3+ was developed. • The RbBaBP 2 O 8 :Tb3+ phosphor exhibits narrow-band green emission with the dominant 5D 4.→7F 5 transition. • The excellent thermal stability and resistance to color shifting is illustrated. [ABSTRACT FROM AUTHOR]

The study of optical and photoluminescence properties of codoped Lu 2 SiO 5 :Ce, Yb single crystals was performed using conventional spectroscopy as well as time-resolved spectroscopy under excitation by pulsed synchrotron radiation. It was shown that the quenching of cerium luminescence is due to the nonradiative energy transfer from Ce3+ to Yb3+ ions. It was confirmed also that such energy transfer is not cooperative process. According to the constructed vacuum referred binding energy diagram the possible mechanism of quenching of cerium luminescence is the metal-to-metal electron transfer from Ce3+ to Yb3+. • The formation of luminescence properties of LSO:Ce,Yb crystals were studied at UV-VUV excitation. • The nonradiative energy transfer from the cerium to ytterbium has been shown. • The energy transfer mechanism is not cooperative. • Vacuum referred binding energy diagram for Lu 2 SiO 5 :Ce,Yb was constructed. [ABSTRACT FROM AUTHOR]

Electronic level schemes with the host valence and conduction band together with the level locations of ground and excited states of defects are used to explain and predict luminescence and carrier trapping phenomena. These schemes are always constructed and interpreted by using the electron picture. In this work the alternative hole picture is presented. Such picture is sometimes used in the field of semi-conductors but hardly ever in the field of wide band gap inorganic compounds. We will focus on the lanthanides, and first show where to draw the hole ground state and excited hole states in our scheme. It leads to up-side-down Dieke diagrams and up-side-down configuration coordinate diagrams but for the rest everything is equivalent to the electron picture. With the hole picture, luminescence quenching via hole ionization to the valence band and hole trapping in defects can be illustrated much more conveniently than with the electron picture. As examples the quenching of the Tb 3 + D 4 5 emissions by electron ionization and the quenching of the Eu 3 + D 0 5 emissions by hole ionization are compared. [ABSTRACT FROM AUTHOR]

Five novel europium β -diketonate complexes containing a pyrazole fragment were investigated. The influence of the number of fluorine atoms in diketonate ligands on luminescent properties was analyzed. Luminescence intensity of Eu 3 + complexes increases significantly when CH bonds with high oscillation energy are replaced with CF bonds with low oscillation energy as the efficiency of energy transfer is improved. Further extension of the fluorinated chain length results in a substantial decrease in non-radiative relaxation rates while the increase in luminescence decay rates is observed. The theoretical results elaborated in terms of Judd-Ofelt theory are in good agreement with the experimental data obtained by time-resolved luminescence spectroscopy. [ABSTRACT FROM AUTHOR]

The effect of posttreatment in HNO 3 at room temperature on the photoluminescence properties and surface chemical bonds of stain etched porous silicon were investigated. It was shown that, such posttreatment results in reversible quenching of photoluminescence. Investigation of the FTIR spectra showed that this posttreatment allows dividing usually occurring simultaneously processes of hydrogen desorption and surface oxidation in two separate processes. It is found that the photoluminescence quenching associated with significant desorption of hydrogen from the surface of porous silicon under the HNO 3 action, and its subsequent recovery associated with surface oxidation in air. This recovery of luminescence is correlated with the appearance of absorption on the oxygen bonds at 1180 cm −1 and 1045 cm −1 . Stability of photoluminescence peak position, despite of changing intensity, both in treated and untreated samples, during exposure to air, correlates with the absorption stability on the oxygen bonds at 1108 cm −1 and 882 cm −1 . These oxygen bonds arise during the formation of stain etched porous silicon and are present in the luminescent and nonluminescent samples. Thus, these oxygen bonds can lead to the occurrence of local levels in the bandgap of silicon nanocrystallites, creating radiative recombination centers. [ABSTRACT FROM AUTHOR]

β-Cyclodextrin (βCD)-coated CdSe/ZnS quantum dots (QDs), provide a sensitive method for the determination of phenolic compounds. The current study aimed to explain the mechanisms involved in photoluminescence quenching of CdSe/ZnS QDs, during the determination of quercetin and gallic acid, and select derivatives thereof. Quercetin, quercetin glycosides, gallic acid and gallate esters, were investigated to understand how the glycoside moiety in glycosides and the hydrocarbon chain in esters, affect the interactions of the investigated polyphenols with βCD-coated QDs. The phenomenon of βCD-coated CdSe/ZnS photoluminescence quenching, is caused by the effective formation of host-guest inclusion complexes between polyphenols and βCD. The presence of the glycoside moiety in the quercetin molecule reduced the effectiveness of the complex formation, while, in contrast, the efficiency of complexation increased with increasing hydrocarbon chain length of the gallate ester molecule. QD photoluminescence quenching may be a consequence of the proximity between the interacting phenolic compounds with the QD surface, rather than βCDs peeling off from the QD surface, resulting in structural destabilization. From the thermodynamic parameters, it was concluded that the formation of the complexes is based both on the van der Waals interactions forces and hydrophobic interactions between guest and host molecules. Ionic interactions may also play an important role in the effectiveness of polyphenol-βCD inclusion complex formation. In order to obtain QDs with long-term stability, there is a need to increase the zeta potential value of the QD surface. Recognition of the above-described mechanisms, should enable the optimization of existing methods and the development of new applications of βCD-coated CdSe/ZnS QDs, such as determination of octyl gallate in foodstuffs. [ABSTRACT FROM AUTHOR]

The aim was to design a multi-chromatic phosphor based on the colour mixing principle, whereby white light can be produced from an appropriate mixture of blue, green, and red emissions by a single phosphor. In this perspective, Tm 2 O 3 , Tb 4 O 7 , and Eu 2 O 3 were simultaneously doped in single host glass matrix. A series of Tm 2 O 3 single- as well as Tm/Tb/Eu triple-doped glasses were synthesised. The photoluminescence behaviour and luminescence quenching were investigated for Tm 2 O 3 single-doped glasses. Keeping Tm 2 O 3 constant at the saturation concentration in the Tm/Tb/Eu triple-doped glasses and varying the doping ratio of the two other lanthanides (Tb 4 O 7 and Eu 2 O 3 ) in the host glass allow to some extent the control of the spectral composition and consequently the generation of tunable colour impressions. The latter can also be adjusted by keeping the concentration ratio of the three lanthanides constant and varying the excitation wavelength. Upon 358-nm excitation of the Tm/Tb/Eu triple-doped glasses, white light emission is achieved and the corresponding correlated colour temperatures are also determined. The different energy transfers occurring in between the three lanthanides are investigated and possible energy transfer routes are proposed. [ABSTRACT FROM AUTHOR]

The luminescence properties of a single crystal of KYb(WO4)2 doped with Tb3+ are investigated as a function of temperature at ambient pressure and at room temperature under high hydrostatic pressure. The observed quenching of the green Tb3+ (5D4→7F5) luminescence is ascribed to a pressure-induced downshift of the Tb3+→W6+ metal to metal charge transfer (impurity trapped exciton) state. A model is introduced to account for the pressure-induced quenching of the Tb3+ luminescence at room temperature in this double tungstate crystal. [ABSTRACT FROM AUTHOR]

We study defect states in Eu-doped Y 3 Al 5 O 12 powder by thermally stimulated luminescence (TSL) in the temperature range 77–500 K. We identify the main TSL peaks, analyze them by the initial rise technique and calculate the characteristic parameters of the corresponding traps. Tunneling of charge carriers between traps and recombination centers up to about 265 K is observed and discussed. Recent study established the presence of both Eu 2+ and Eu 3+ centers in the studied Y 3 Al 5 O 12 powder. The TSL spectra show that Eu 2+ and Eu 3+ centers compete in the charge carrier capture. We show that previously observed Eu 2+ luminescence quenching is due to both classical thermal quenching and thermal ionization of the Eu 2+ excited state. We model the temperature dependence of the delayed recombination intensity. [ABSTRACT FROM AUTHOR]

Defects inside fluorescent materials are often an important cause of the anti-thermal quenching of fluorescent materials. Adjusting the thermal compensation effect of defects on luminous centers is often achieved by adjusting the types, quantities and depths of defect traps. In this contribution, we found that doping Ga3+ into LiTaO 3 matrix containing intrinsic defects of lithium vacancies (V L i ，) and antisite-tantalum ( T a L i 4 + ) resulted in Bi3+ from non-luminescence to luminescence. It is speculated that the luminescence is mainly due to the charge compensation of Ga3+ instead of Ta5+, which promotes the conversion from Bi2+ to Bi3+, and then makes phosphor produce obvious luminescence. Interestingly, due to the increase of Ga3+ content, when excited at 304 nm, the integral intensity of sample (0.10 Ga3+) at 420–470 nm is 1.98 times that of sample (0.01 Ga3+). The effect of defect traps on luminescent properties was characterized by thermoluminescence (TL) and X-ray photoelectron spectroscopy (XPS). It is confirmed that the thermal compensation from 303 to 383 K comes from V O · · , B i L i 2 + , T a L i 4 + and G a L i 2 + . And the proportion of these defects will change with the change of the heterovalent substitution of Ga3+/Ta5+. At the same time, the increase of Ga3+ concentration from 1 to 10% in defect modification results in the change of crystal structure, which also increases the Bi3+ band gap from 3.40 eV to 3.50 eV, thus increasing the proportion of the integral intensity of 423 K to original intensity of 303 K at 420–470 nm from 0.45 to 0.67. This defect engineering strategy of Ga3+ modification is helpful for a more complete understanding of the causes for the change of luminescence and thermal quenching characteristics of phosphors in the process of heterovalent substitution, as well as the development of anti-thermal quenching phosphors for high-quality w-LEDs. [Display omitted] [ABSTRACT FROM AUTHOR]

The spectral-kinetic characteristics of Nd3+ optical centers (A, B, C centers) in Sr 3 LaNb 3 O 12 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(N 1) = 55 cm−1/2, γ(N 2) = 95 cm−1/2) and microparameters (C DA = 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 R min. = 0.45 nm, and the boundary time at which the ordered luminescence quenching stage changes for disordered one is determined as t bound. ∼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 (τ D <τ A) are determined. • Perovskite crystals (Sr 3 LaNb 3 O 12 :Nd3+) have been studied as promising materials for solar cells and neutron detectors. • Possible channels for the transfer of electronic excitation energy between the optical centers of Nd3+ ions have been established. • The macro- and micro-parameters of the interionic interaction of Nd3+ - Nd3+ were determined. [ABSTRACT FROM AUTHOR]

A series of near-UV to blue emitting Sr 3 Lu 2 (Si 3 O 9 ) 2 :Ce 3+ phosphors were prepared by a solid state reaction. The optical properties of synthesized phosphors were investigated as a function of Ce 3+ concentration and temperature. These luminescent materials strongly absorb UV radiation shorter than 360 nm. The optimal Ce 3+ concentration was 0.1% (external quantum efficiency ca. 45%). Temperature dependent measurements showed that Sr 3 Lu 2 (Si 3 O 9 ) 2 :Ce 3+ phosphors possess good thermal stability and loses only about 40% to 50% of initial intensity in the temperature range of 77–500 K depending on activator concentration. [ABSTRACT FROM AUTHOR]

The determination of histamine based upon the photoluminescence static quenching of thioglycolic acid modified CdTe quantum dots (TGA-CdTe QDs) is proposed. Under optimum conditions, the analytical response followed a Stern-Volmer model. Experimental conditions were adjusted to enable a robust and reproducible analytical response. The linear response observed in the QDs aqueous dispersion covered the histamine concentration from 9.6×10 −6 mol L −1 (1.1 µg mL −1 ) to 5.7×10 −4 mol L −1 (63 µg mL −1 ). The approach was tested in the analysis of fresh and canned tuna fish samples after cationic solid phase extraction, in order to improve selectivity of determination. Analytical results of the eluted extracts were compared to the ones achieved with a reference spectrophotometric method using a concentration range that can be accessed by both methods and also by liquid chromatography with mass detection. Satisfactory recoveries were achieved for both canned and fresh tuna fish samples. The application in real samples has been demonstrated at the mg kg −1 level. The possible mechanism for histamine quenching is investigated. [ABSTRACT FROM AUTHOR]

Chemosensor C1 , namely, 3-acetoacetyl-7-hydroxycoumarin, was synthesized and exhibited highly selective and sensitive fluorescence sensing ability for Cu 2+ over other metal ions under physiological conditions. The fluorescence quenching response of C1 for Cu 2+ indicated that C1 can be used as an on-off fluorescent chemosensor to selectively detect Cu 2+ . The binding process was confirmed by UV–vis absorption, fluorescence measurement, mass spectroscopy, IR spectra and DFT calculation. To test the practical use of the probe, the determination of Cu 2+ in real water samples was evaluated. The application of the fluorescent probe in monitoring intracellular Cu 2+ in HeLa cells has also been demonstrated. [ABSTRACT FROM AUTHOR]

A novel Pr 3+ ions doped red phosphor Ca 19 Mg 2 (PO 4 ) 14 :Pr 3+ was first synthesized and the phase purity as well as the characteristic photoluminescence property was investigated through X-ray diffraction, diffuse-reflectance and photoluminescence spectra measurement. The analysis revealed that Ca 19 Mg 2 (PO 4 ) 14 :Pr 3+ had strong absorption from 450 to 470 nm and could exhibit red emission peaking around 610 nm under 450 nm excitation. The emission quenching behavior of 1 D 2 – 3 H 4 transitions via increasing the Pr 3+ contents was investigated and the mechanism was discussed in detail. The temperature dependent emission spectra of Ca 19 Mg 2 (PO 4 ) 14 : x Pr 3+ with different doping contents ( x =0.002 and x =0.02) were studied and the abnormal thermal quenching property was investigated. [ABSTRACT FROM AUTHOR]

Today, the development of broadband optical amplifiers for optical communication applications continues to motivate research into rare earth ion (RE)-activated near-infrared (NIR) emissive materials. Pr3+-doped BiLa 2 O 4.5 phosphors were prepared via the facile solid-state reaction. The phase formation, structural characteristics, and broadband NIR emission of Pr3+ ions are presented. Unlike commonly reported materials activated by Pr3+ ions, 1320 nm luminescence, that usually applied as an amplifier technology in O-band optical communication, has not been detected in BiLa 2-2 x Pr 2 x O 4.5 (x = 0.005–0.05). However, BiLa 2-2 x Pr 2 x O 4.5 shows a broad 1D2→1G4 emission (1400 nm–1550 nm) extending over the E−, S -, and C - bands in optical communication, and its full-width at half-maximum (FWHM) can reach 143 nm at room temperature. Pr3+-doped BiLa 2 O 4.5 is expected to serve as a potential candidate for amplifier materials in E− and S -band communication system technologies. The quenching of the 1320 nm luminescence in BiLa 2-2 x Pr 2 x O 4.5 was discussed via the energy gap based on the high-energy phonons of the host. The maximum doping concentration to achieve maximum near-infrared luminescence (1400 nm–1550 nm band) in BiLa 2-2 x Pr 2 x O 4.5 is x = 0.03. The concentration quenching and luminescence mechanism are discussed via cross-relaxation. • Pure-phased BiLa 2 O 4.5 :Pr3+ was prepared by a simple solid-phase reaction. • 1320 nm emission used in O-band optical communication was not detected. • 1D2.→1G4 emission has broad FWHM of 143 nm at 300 K extending over E−, S -, and C - bands. • 1D2.→1G4 emission exhibits an abnormal temperature dependence (10–300 K). • Concentration quenching and luminescence mechanism were discussed. [ABSTRACT FROM AUTHOR]

A polycrystalline Eu 2 Mo 4 O 15 phosphor sample was prepared by high temperature solid state reaction. Phase purity and morphological features of the phosphor were investigated by X-ray diffraction and scanning electron microscopy, respectively. Reflectance spectra showed that the optical band gap of Eu 2 Mo 4 O 15 is 2.95 eV. Phosphor emits intensive red light when excited with 394 and 465 nm radiation. Temperature dependent emission and luminescence lifetime measurements revealed that external and internal quantum yields decrease at the same rate and that luminescence quenches due to photoionization. The calculated external quantum yields for 394 and 465 nm excitation were 7.8% and 53.5%, respectively. [ABSTRACT FROM AUTHOR]

A novel red phosphor Ba 2 Si 4 O 10 : Eu 3+ was synthesized by the high-temperature solid state reaction method in air atmosphere. The crystal results reveal that Ba 2 Si 4 O 10 has two different phases, in which the high-temperature phase belongs to monoclinic system and exhibits better photoluminescence property compared with low-temperature phase. The monoclinic Ba 2 Si 4 O 10 was obtained at 1250 °C and matched well with the JCPDS Card No. 83-1446. Photoluminescence excitation and emission spectra, fluorescence lifetime and quantum yield are conducted to investigate the luminescent property of Ba 2 Si 4 O 10 : Eu 3+ phosphor. The results show that the phosphor can be excited by 393 nm light ( 7 F 0 → 5 L 6 ) effectively and emit a strong red emission at 612 nm ( 5 D 0 → 7 F 2 ). The optimal concentration of Eu 3+ ions in Ba 2 Si 4 O 10 matrix is 0.02, where the fluorescence lifetime was 1.0837 ms and the quantum yield was up to 31.64%. Additionally, the chromaticity coordinates of the optimal composition Ba 1.98 Si 4 O 10 : 0.02Eu 3+ phosphor is calculated to be (0.65, 0.34). These results suggest that Ba 2 Si 4 O 10 : Eu 3+ phosphor could be a potential red phosphor for practical application and optical devices. [ABSTRACT FROM AUTHOR]

Tb 3+ or/and Cr 3+ doped or co-doped Y 3 Al 5 O 12 (YAG) garnets were prepared by a citric acid sol–gel method. Single-phase YAG, YAG:Tb 3+ ,YAG:Cr 3+ and YAG:Cr 3+ ,Tb 3+ powders were obtained already at 1000 °Cand were further annealed at 1600 °C to increase the crystallinity. All materials were characterized by X-ray diffraction (XRD), thermogravimetric (TG), photoluminescence (PL), reflection and photoluminescence decay measurements. Scanning electron microscopy (SEM) was used for morphology description. Luminescence measurements indicated that Tb 3+ ions located at dodecahedral sites transfer absorbed energy to Cr 3+ ions located at octahedral sites resulting quenched Tb 3+ and strengthened Cr 3+ emission in YAG:Cr 3+ , Tb 3+ upon 273 nm excitation. [ABSTRACT FROM AUTHOR]

The strongly luminescent and highly oxygen-sensitive Tb(III) complex [{(MeMeArO) 3 tacn}TbIII(THF)] (denoted hereafter as [ 1 Tb THF]) was studied with density functional theory (DFT) and wavefunction-based ab initio electronic structure methods combined with Tb relativistic ab initio pseudopotentials. The optimized geometries as well as the calculated UV–vis absorption spectra at the DFT level agree well with the available experimental data. The calculated vertical S 0 */5D 4 → S 0 */7F J (ligand/Tb3+ states) emission energies for J = 0–6 at the RSPT2//CASSCF level including spin-orbit corrections are 475, 511, 549, 583, 614, 638, and 644 nm, respectively, and are lower by 15, 36, 39, 39, 39, 35, and 35 nm, respectively, than the corresponding experimental values. The luminescence quenching mechanism of [ 1 Tb THF] in presence of O 2 was investigated. RSPT2//CASSCF calculations for [ 1 Tb THF]·O 2 indicate that the S 0 */7F J (J = 0–6)/1O 2 (1Δ g or 1Σ+ g) states (ligand/Tb3+/O 2 states) are energetically more stable than the emission states S 0 */5D J (J = 0–4)/3O 2 (3Σ- g). Therefore, after initial photo excitation of the ligand and subsequent energy transfer to the Tb3+ ion, the energy will be further transferred to O 2 leading to the observed luminescence quenching of [ 1 Tb THF] in air. A comparison is made to [ 1 Sm THF]·O 2 which shows a significantly smaller luminescence quantum yield and no oxygen quenching. [Display omitted] • Quantum chemical study of the complex [{(MeMeArO) 3 tacn}TbIII(THF)] ([ 1 Tb THF]). • Structures, UV–vis absorption and emission spectra agree with experimental data. • Explanation why [ 1 Tb THF] shows strong luminescence and O 2 quenching. • Explanation why [ 1 Sm THF] shows weak luminescence and no O 2 quenching. [ABSTRACT FROM AUTHOR]