Quenching of electronically excited Ln3+* ions by C60 fullerene

Quenching of electronically excited states of Ln^3+* ions generated upon photoexcitation of toluene solutions of Ln(acac)₃·H₂O (Ln = Tb, Eu) complexes by C₆₀ fullerene at 293 K was detected and investigated. The dependences of quenching efficiency on C₆₀ concentration obtained from data on the decrease in the photoluminescence intensity and Ln^3+* lifetimes obey the Stern-Volmer law. Quenching is due to inductive-resonant energy transfer from Ln^3+* to C₆₀ fullerene. The bimolecular rate constants for quenching, the overlap integrals of the Ln^3+* photoluminescence spectra with the C₆₀ absorption spectra, and the critical energy transfer distances were determined. No sensitized luminescence of C₆₀ in the system studied was detected. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 921–925, June, 2006.     

ZnAl2O4:Mn材料的制备及发光性能

以共沉淀法与煅烧法联用,成功制备了一系列ZnAl₂O₄:xMn样品。通过扫描电镜和X射线粉末衍射测试研究了样品的形貌和物相特征,结果表明尖晶石结构的ZnAl₂O₄中[AlO₆]的八面体位可以有效被Mn⁴⁺替代。通过荧光激发和发射光谱研究了样品的发光性能,发现Mn⁴⁺在ZnAl₂O₄体系中掺杂可以显示出明亮的红色发光(发射峰值位于680 nm处)。比较不同Mn⁴⁺浓度(Mn与Al的物质的量之比)掺杂样品的发光强度时发现,Mn⁴⁺最佳掺杂浓度为0.06%。通过德克斯特公式分析了发光强度与浓度关系,探究浓度猝灭机制,结果表明最邻近离子之间能量传递造成Mn⁴⁺浓度猝灭的发生。为了提高Mn⁴⁺的发光强度,选择了7种金属离子(Li⁺、Na⁺、K⁺、Ca²⁺、Sr²⁺、Sn²⁺和Ga³⁺)与Mn⁴⁺共掺杂进入ZnAl₂O₄基质中,其中效果较突出的为Li⁺和Ga³⁺,其共掺杂使Mn⁴⁺发光强度分别增强0.6倍和1倍。     

Obtain full visible spectrum light-emitting diode illumination via bismuth-activated cyan phosphors

Developing highly efficient cyan-emitting fluorescent materials is essential to bridge the cyan gap in phosphor-converted white light-emitting diodes for full-spectrum white illumination. Here, a Bi-doped cyan phosphor has been reported to solve this gap. The phase purity, photoluminescence emission/excitation spectra, concentration quenching, lifetime decay curves, and temperature-dependent photoluminescence emission spectra were systematically investigated. SrLaGaO₄:Bi³⁺ exhibits a broad excitation band (250–400 nm), which matches with the emission of a commercial near-ultraviolet light-emitting diode chip. The cyan light peaked at 475 nm is observed, which is attributed to the ³P₁→¹S₀ transition of Bi³⁺. The thermal quenching experiment was performed, and the activation energy was calculated as 0.36 eV. Finally, full-spectrum white light-emitting diode devices were fabricated using SrLaGaO₄:Bi³⁺ phosphors, commercial blue BaMgAl₁₀O₁₇:Eu²⁺ phosphor, green (Ba, Sr)₂SiO₄:Eu²⁺ phosphor, and red CaAlSiN₃:Eu²⁺ phosphor, which displayed an International Commission on an illumination coordinate of (0.3732, 0.3850), a correlated color temperature of 4290 K, and a color rendering index of 93.2 at a drive current of 20 mA. This result indicates that SrLaGaO₄:Bi³⁺ plays an essential role in bridging the cyan gap, providing new inspiration for applying cyan-emitting phosphors in full-spectrum white lighting.     

Thermally stable deep-red emitting Sr2GdTaO6:Mn4+ double perovskites for indoor plant growth LEDs

Indoor artificial cultivation of plants is a novel technology applied to agriculture, and the emission band of luminescent materials can be matched with the needs of plants to promote plant growth. In this contribution, novel Mn⁴⁺ doped Sr₂GdTaO₆ (SGTO) deep-red phosphor was synthesized. This material was characterized, in detail, by X-ray diffractometer, SEM, and photoluminescence emission spectra. Sr₂GdTaO₆:Mn⁴⁺ (SGTO:Mn⁴⁺) can be effectively excited by near-ultraviolet (NUV) light, and the broadband emission of deep-red light matches the absorption band of plant phytochromes P_R and P_FR. The optimum doping concentration of Mn⁴⁺ in SGTO was 0.6 mol%, and the concentration quenching mechanism was attributed to dipole-quadrupole (d-q) electric interaction. The photoluminescence emission intensity of SGTO:0.006Mn⁴⁺ at 423 K is 80.6% of that at room temperature and the internal quantum efficiency of SGTO:0.006Mn⁴⁺ is 36.09%. Finally, the performance of the commercial 440 nm light-emitting diode chip/SGTO:0.006Mn⁴⁺ encapsulated light-emitting diode device was stable and can meet the needs of plants for the blue and red light. The results showed that SGTO:0.006Mn⁴⁺ deep-red phosphor is expected to be a phosphor suitable for indoor plant growth lighting.     

Spectroscopic investigation of La7Ta3W4O30:Sm3+ orange-red phosphor for white LEDs

The novel orange-red light emitting La₇Ta₃W₄O₃₀:xSm³⁺ (x = 0.005–0.20) phosphors were synthesized via the solid-state reaction method. The crystal structure, photoluminescence (PL) properties, optimum concentration, color purity, decay life, and thermal stability of the samples were systematically studied. Under the excitation of 404 nm, La₇Ta₃W₄O₃₀:Sm³⁺ emits intense orange-red light at 597 nm. The PL spectra of La₇Ta₃W₄O₃₀:Sm³⁺ phosphors are ascribed to the ⁴G_5/2 to ⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm³⁺ ions. The concentration quenching occurs at the doping level of 1 mol%. The quenching temperature is higher than 500 K. Finally, a white LED (w-LED) with the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of (0.312, 0.296) and good color rendering index (Ra) of 86 was fabricated. As a consequence, all the results suggest that the orange-red phosphors La₇Ta₃W₄O₃₀:Sm³⁺ have potential applications in w-LEDs structures.     

Multibubble sonoluminescence of Tb3+ ion in aqueous solutions of dimethyl sulfoxide

The intensity and spectra of multibubble sonoluminescence of TbCl₃ solutions in water-DMSO mixtures saturated with air and argon are studied. The spectra represent the superposition of the characteristic glow of Tb³⁺ ions and the continuum of emission of electronically excited products of solvent sonolysis (with H₂O*, OH*, and SO₂* as main emitters). Abnormal action of DMSO and sulfur dioxide on the characteristic luminescence of Tb³⁺ ions during sonolysis of aqueous solutions is revealed. These additives enhance the sonoluminescence of water to different extent, quench the sonoluminescence of Tb³⁺, and differently influence the photoluminescence quantum yield of this ion (DMSO acts as activator, whereas SO₂ acts as quencher). Sulfur dioxide quenches the sonoluminescence of Tb3+ much more efficiently than the photoluminescence of Tb³⁺. The abnormal effect of DMSO on sonoluminescence is most probably due to the quenching action of sulfur dioxide formed during sonolysis of DMSO on Tb³⁺* ions in cavitation bubbles.     

Quantitative determination of site occupancy of multi-rare-earth elements doped into Ca2SnO4 phosphor by electron channeling microanalysis

X-ray fluorescence analysis based on electron channeling effects in transmission electron microscopy (TEM) was performed on Ca₂SnO₄ phosphor materials doped with Eu³⁺/Y³⁺ at various concentrations, which showed red photoluminescence associated with the ⁵D₀-⁷F₂ electric dipole transition of Eu³⁺ ions. The method provided direct information on which host element site dopant elements occupy, the results of which were compared with those of X-ray diffraction (XRD)-Rietveld analysis. The obtained results indicated that while it is not favorable for a part of Eu³⁺ to occupy the smaller Sn⁴⁺ site, this is still energetically better than creating Ca vacancies or any other of the possible charge balance mechanisms. The local lattice distortions associated with dopant impurities with different ionic radii were also examined by TEM-electron energy-loss spectroscopy (TEM-EELS). The change in PL intensity as a function of dopant concentration is discussed based on the experimental results, although the general concept of concentration quenching applies.     

Distribution-related luminescence of Eu sensitized by SnO2 nano-crystals embedding in oxide glassy matrix

Eu³⁺ doped transparent glass ceramics embedding SnO₂ nano-crystals were prepared by melt quenching and subsequent heating. Site selective excitation experiments revealed that some Eu³⁺ ions were incorporated in the SnO₂ lattices by substituting Sn⁴⁺ ions, whereas the rest located in the oxide glassy matrix. Interestingly, it is found that the Eu³⁺ ions residing in the SnO₂ lattices exhibited much longer luminescent decay lifetime than those in the glassy matrix. Measurements on the photoluminescence excitation and photoluminescence spectra demonstrated the occurrence of energy transfer from the SnO₂ nano-crystals to the Eu³⁺ ions. The influences of Eu³⁺ content, and furthermore, their location on the energy transfer process were discussed.     

Multimode Luminescence Tailoring and Improvement of Cs2NaHoCl6 Cryolite Crystals via Sb3+/Yb3+ Alloying for Versatile Photoelectric Applications

Lead-free halide double perovskites are currently gaining significant attention owing to their exceptional environmental friendliness, structural adjustability as well as self-trapped exciton emission. However, stable and efficient double perovskite with multimode luminescence and tunable spectra are still urgently needed for multifunctional photoelectric application. Herein, holmium based cryolite materials (Cs₂NaHoCl₆) with anti-thermal quenching and multimode photoluminescence were successfully synthesized. By the further alloying of Sb³⁺ (s-p transitions) and Yb³⁺ (f-f transitions) ions, its luminescence properties can be well modulated, originating from tailoring band gap structure and enriching electron transition channels. Upon Sb³⁺ substitution in Cs₂NaHoCl₆, additional absorption peaking at 334 nm results in the tremendous increase of photoluminescence quantum yield (PLQY). Meanwhile, not only the typical NIR emission around 980 nm of Ho³⁺ is enhanced, but also the red and NIR emissions show a diverse range of anti-thermal quenching photoluminescence behaviors. Furthermore, through designing Yb³⁺ doping, the up-conversion photoluminescence can be triggered by changing excitation laser power density (yellow-to-orange) and Yb³⁺ doping concentration (red-to-green). Through a combined experimental-theoretical approach, the related luminescence mechanism is revealed. In general, by alloying Sb³⁺/Yb³⁺ in Cs₂NaHoCl₆, abundant energy level ladders are constructed and more luminescence modes are derived, demonstrating great potential in multifunctional photoelectric applications.     

Promising photoluminescence optical approach for triiodothyronine hormone determination based on smart copper metal–organic framework nanoparticles

A copper metal–organic framework nanoparticles (Cu‐MOF‐NPs) synthesized via simple technique. The prepared Cu‐MOF‐NPs nanoparticles were further characterized using ¹H‐NMR, FE‐SEM/EDX and thermal study (DSC/TGA). The FE‐SEM/EDX, thermal analysis, and NMR spectrum data with the other analysis support the nano‐Cu‐MOF structure and the monomeric unit (n[Cu (AIP)₂(APY)(H₂O)₂].4H₂O) of Cu‐MOF‐NPs. The photoluminescence (PL) studies of triiodothyronine hormone (T3) based on the prepared Cu‐MOF‐NPs investigated. The results revealed that the Cu‐MOF‐NPs might be used as a biosensor in the determination of triiodothyronine hormone (T3) in biological fluids through a significant quenching of the photoluminescence intensity of Cu‐MOF‐NPs at excitation wavelength 492 nm. The calibration plot achieved over the concentration range 0.0–200.0 ng/dL T3 hormone with a correlation coefficient 0.996 and limit of detection (LOD) and quantification (LOQ) 0.198 and 0.60 ng/dL, respectively. The PL spectra are indicating that Cu‐MOF‐NPs has highly selective sensing properties for T3 hormone without interfering with other human many hormones types. This approach considered a promising analytical tool for early diagnosis of the cases of thyroid disease. The mechanism of quenching between the Cu‐MOF‐NPs, and T3 hormone studied. The mechanism was a dynamic type and obtained due to the energy transfer mechanism.     

Synthesis,characterization, and photoluminescence of SrBPO5:R,Na+ (R = Eu3+, Tb3+) phosphor for solid state lighting

A series of phosphors SrBPO₅:R,Na⁺ (R = Eu³⁺, Tb³⁺) were prepared by high-temperature solid-state synthesis, and their phase purity, morphology, IR spectra, and UV-Vis photoluminescence properties were investigated. The f-f transitions of Eu³⁺ and Tb³⁺ ions in the host lattice were assigned and discussed. The excitation and emission spectra indicate that SrBPO₅:Eu³⁺,Na⁺ and SrBPO₅:Tb³⁺,Na⁺ can be effectively excited by ultraviolet (394 and 370 nm), and exhibit reddish orange emission and yellowish green emission, respectively. The influence of the doping concentration on the relative emission intensity of Eu³⁺/Tb³⁺ was investigated, and the critical distance R_c was estimated in term of the concentration quenching data. The present study suggests SrBPO₅:R,Na⁺ (R = Eu³⁺, Tb³⁺) phosphor can be a potential candidate as an UV-convertible phosphor for white light-emitting diodes (LEDs).     

Controlling the Dual-Emission Character of Aryl-Modified o-Carboranes by Intramolecular CH⋅⋅⋅O Interaction Sites

It is still challenging to realize a dual-emission system, in which two luminescent bands simultaneously appear by photoexcitation, in solid with organic dyes due to the difficulty in regulation of electronic properties in the excited state and concentration quenching. o-Carborane is known to be a versatile platform for constructing solid-state emitters since the sphere boron cluster is favorable for suppressing intermolecular interactions and subsequently concentration quenching. Here, we show solid-state dual-emissive o-carborane derivatives. We prepared 4 types of o-carborane derivatives and found dual-emission behaviors both in solution and solid states. By regulating the rotation at the o-carborane unit with the intramolecular C_cageH⋅⋅⋅O interaction, the dual-emission intensity ratios were changed. Finally, it was demonstrated that the overall photoluminescence spectra can be estimated using the binding energy of intramolecular interactions.     

Synthesis and characterization of novel blue emitting Na2CaSiO4:Ce3+ phosphor

The blue phosphors Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ were synthesized by the sol–gel method and their luminescence characteristics were investigated for the first time. Structural information about prepared samples is obtained by analyzing the XRD patterns and SEM micrographs. The photoluminescence (PL) excitation spectra indicate that the Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ phosphors can be effectively excited by ultraviolet (360 nm) light. The PL emission spectra exhibit tunable blue broadband emission with the dominant wavelength of 427–447 nm under excitation of 360 nm by controlling the doping concentration of Ce³⁺. The concentration quenching effect for Ce³⁺ was found at the optimum doping concentration of 4 mol%. The Commission Internationale de l’Eclairage 1931 chromaticity coordinates of Na_1.96Ca_0.96SiO₄:0.04Ce³⁺ are (0.1447, 0.0787), which are better color purity compared to the commercial Eu²⁺-doped BaMgAl₁₀O₁₇ phosphor. Na_1.96Ca_0.96SiO₄:0.04Ce³⁺ composition shows intense blue emission (peak wavelength, 439 nm) with relative intensity versus commercial BaMgAl₁₀O₁₇:Eu²⁺ blue phosphor (Nichia) 65 and 158 % under 254 and 365 nm excitation, respectively. All the results indicate that Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ phosphors are potential candidate as a blue emitting phosphor for UV-converting white light-emitting diodes.     

The influence of the temperature of a liquid on multibubble sonoluminescence of Tb3+ ions in an aqueous solution

The influence of temperature on the yield of multibubble sonoluminescence of Tb³⁺ ions in an aqueous solution of TbCl₃ was studied over the temperature range 5–55°C. The yield monotonically decreased as the temperature increased. The effective activation energy of this temperature quenching was larger than that of photoluminescence of terbium but smaller than for solvent sonoluminescence quenching. The result obtained was explained using the earlier suggested hypothesis of intrabubble f-f excitation of lanthanide ions in the sonolysis of aqueous solutions and two-stage (in the gas and liquid phases) deactivation of their long-lived (longer than 10^?4 s) excited states in a bubble medium.     

Hydrothermal homogeneous urea precipitation of hexagonal YBO3:Eu nanocrystals with improved luminescent properties

Well-crystallized YBO₃:Eu³⁺ nanocrystals were prepared by a mild hydrothermal method in the presence of urea, and a pure hexagonal phase could be obtained at a low temperature of 200°C only. The photoluminescence spectra showed a remarkable improvement on the chromaticity as well as the luminescent intensity, compared with the samples synthesized by solid-state reaction (SR). The effects of the synthesis temperature, urea concentration, and the doping concentration of Eu³⁺ on the crystallization and luminescent properties were investigated. The results showed that both high temperature and low urea concentration were favorable to the formation of YBO₃:Eu³⁺, and the ratio of red emission (⁵D₀→⁷F₂) to orange emission (⁵D₀→⁷F₁) increased with decreasing the synthesis temperature and the urea concentration. Furthermore, the samples exhibited a higher quenching concentration of Eu³⁺ in comparison with those prepared by the SR, which was beneficial to further enhancing the luminescent intensity. These synthesis-dependent phenomena were analyzed, and possible explanations were proposed.     

Structure and optical properties of cerium(III)-doped PbWO4 micro-crystals synthesized by a facile wet chemical method

Cerium(III) doped PbWO₄ micro-crystals with different doping contents were synthesized via a facile wet chemical method in air atmosphere at room temperature. X-ray diffraction patterns of as-synthesized powders revealed that these micro-crystals were pure scheelite PbWO₄, without any impurities such as Ce₂(WO₄)₃ and PbO, and Ce³⁺ could enter into Pb²⁺ sites, which would induce the formation of lead vacancies in the PbWO₄ crystal lattice. The UV–vis diffuse reflection spectra, Raman spectra and photoluminescence (PL) spectra of doped and pure PbWO₄ micro-crystals were studied in detail, which indicated that optical properties of doped PbWO₄ were greatly changed. The adsorption edge of Ce(III)-doped PbWO₄ micro-crystals would shift toward high wavelength (red-shift) with gradually increasing Ce³⁺ doping concentration. It shows an obvious decrease in blue emission band which made the shape of the whole emission band remodeled with the Ce³⁺ doping.     

Emission Properties of the Plasma in Mixtures of Helium with Diethylzinc and Hydrogen Selenide Vapors

The emission properties in the range 200-600 nm of the low-temperature plasma in mixtures of He with Et₂Zn and H₂Se vapors were studied. The spectrum of emission accompanying decomposition of Et₂Zn includes 26 identified lines of Zn atoms and strong emission of electronically excited CH* radicals, and in the case of decomposition of H₂Se two emission lines of Se atoms and an emission band of SeH* radicals are observed. The rate constants of quenching of the levels He 4d ³ D _2,1 and 3p ¹ P ₁ on introduction into the He plasma of Et₂Zn and H₂Se vapors were determined; Et₂Zn is a stronger quenching agent than H₂Se. Analytical lines allowing monitoring of ZnSe film deposition were selected. Direct plasmochemical decomposition of mixtures of Et₂Zn with H₂Se results in growth of textured ZnSe(cub) layers with substantial inclusions of the hexagonal phase and with carbon-containing inclusions. The photoluminescence spectra of the films obtained exhibit a strong edge band at 460 nm, overlapping with a strong self-activated band centered at 540 nm.     

Characterization of the Interaction Between Caffeine and Soybean Selenoprotein by Spectroscopic and Cyclic Voltammetric Methods

The quantitative interaction of soybean selenoprotein (SSP) with caffeine (CAF) has been studied by fluorescence, cyclic voltammetry and resonance Rayleigh scattering (RRS) spectra. Fluorescence results demonstrate that the quenching of SSP, induced by CAF, can mainly be attributed to static quenching, and the relative contribution of dynamic quenching is about 0.37% by using a Stem–Volmer analysis. The binding constant (K _a) and binding sites (n) of the formed SSP/CAF complex at 293 K calculated from the fluorescence quenching results were found to be 4.29 × 10⁴ L·mol^?1 and 1.22, respectively, which is relatively consistent with the corresponding values obtained by cyclic voltammetry. Based on Förster’s theory, the average binding distance (r) between CAF and SSP was found to be 3.03 nm. The interaction mechanism between CAF and SSP was also supported by inspecting the RRS spectra. The effect of CAF on the conformation of SSP was investigated by using the fluorescence phase diagram and circular dichroism spectra. The experimental results show that SSP binding to CAF follows the two-state model and the helical content of SSP decreases after the interaction. In addition, the effect of CAF on the antioxidant activity of SSP was revealed by ultraviolet spectrophotometry. According to the results, SSP/CAF possesses significantly higher antioxidant activity than the control soybean selenoprotein.     

The influence of the temperature on the carbonate complexation of uranium(VI): a spectroscopic study

The interaction of uranium(VI) with carbonate ions was studied with absorption spectroscopy and time-resolved laser-induced fluorescence spectroscopy due to the importance of these complexes in environmental relevant waters. In the pH range from 2 to 11 the influence of the temperature on the spectra was studied to check changes in the abundances of several binding forms. It was found that several binding forms are predominant at different temperatures and pH values. This observation can be explained by speciation changes due to the dependence of chemical equilibria on the temperature. Furthermore photoluminescence spectra of aqueous solutions of uranyl carbonate complexes were observed at ambient temperatures for the first time and single component absorption spectra of the uranyl carbonate complexes UO₂(CO₃)₃ ⁴⁻ and UO₂(CO₃)₂ ²⁻ were derived.     

Photophysical and Photochemical Properties of Ru(bpy)3 2+ in Si-Ti Mixed Oxides Xerogels Prepared by the Sol-Gel Process

The luminescence spectra and lifetime of tris(2,2-bipyridine)ruthenium(II), Ru(bpy)₃ ²⁺, were studied in sol-gel reaction systems of tetramethoxysilane (TMOS) and titanium(IV) isopropoxide (TTIP) with HCl. Luminescence lifetime in the TMOS system increased as the sol-gel reaction proceeded, because diffusion-controlled luminescence quenching such as oxygen and collisional quenching with solvent molecules were suppressed in the rigid matrices. On the other hand, luminescence lifetime in the TTIP system decreased during the sol-gel reaction. The decrease in lifetime was ascribed to electron transfer from photoexcited Ru(bpy)₃ ²⁺ to the conduction band of the TiO₂ xerogels. Extended X-ray absorption fine structure (EXAFS) measurements were done to associate lifetime in the Si-Ti xerogels with the structures of Ti⁴⁺ sites in the xerogels.