Luminescent Properties of Hybrid Nanostructures Based on Quantum Dots of CdS,Europium 1,3-Diketonate,and Methylene Blue Molecules

The luminescent properties of hybrid nanostructures constructed from colloidal quantum dots (QDs) of CdS passivated with thioglycolic acid, europium(III) tris(tenoyltrifluoroacetonate), and methylene blue dye molecules are studied. Spectral features typical for the formation of core/shell QDs of the CdS/CdS:Eu³⁺ type are found. It is noted that the adsorption of the europium complex at the QD interfaces and the formation of QDs of the CdS/TGA/Eu³⁺ are probable. Spectral patterns that reveal nonradiative energy transfer from the recombination luminescence centers of CdS QDs to the Eu³⁺ ions in the CdS/CdS:Eu³⁺ and CdS/TGA/Eu³⁺ structures are obtained. This is manifested in quenching the recombination luminescence of QDs and in the ignition of the intracentric luminescence of Eu³⁺, which enhance with an increase in the concentration of the europium complex. When such structures are combined with methylene blue molecules, the half-width of the absorption spectra is found to increase by 10–15% with an unchanged position of the absorption band maximum. With an increase in the concentration of methylene blue molecules, decreases in the intensity of the recombination luminescence band of CdS QDs at a wavelength of 530 nm and in the luminescence intensity of Eu³⁺ ions and simultaneously the rise up of the fluorescence of methylene blue at a wavelength of about 675 nm are observed. At the same time, a decrease in the luminescence lifetime of the bands of QDs and europium ions are observed. It is concluded that the nonradiative excitation energy transfer from both the recombination luminescence centers and Eu³⁺ ions to methylene blue molecules takes place.     

Re-dispersible Li<Superscript>+</Superscript> and Eu<Superscript>3+</Superscript> co-doped CdS nanoparticles: Luminescence studies

Re-dispersible CdS, 5 at.% Eu³⁺-doped CdS, 2 at.% Li⁺ and 5 at.% Eu³⁺ co-doped CdS nanoparticles in organic solvent are prepared by urea hydrolysis in ethylene glycol medium at a low temperature of 170°C. CdS nanoparticles have spherical shape with a diameter of ∼80 nm. The asymmetric ratio (A ₂₁) of the integrated intensities of the electrical dipole transition to the magnetic dipole transition for 5 at.% Eu³⁺-doped CdS is found to be 3.8 and this ratio is significantly decreased for 2 at.% Li⁺ and 5 at.% Eu³⁺ co-doped CdS (A ₂₁ = 2.6). It establishes that the symmetry environment of Eu³⁺ ion is more favored by Li-doping. Extra peak at 550 nm (green emission) could be seen for 2 and 5 at.% Eu³⁺ co-doped CdS. Also, the significant energy transfer from host CdS to Eu³⁺ is found for 5 at.% Eu³⁺-doped CdS compared to that for 2 at.% Li⁺ and 5 at.% Eu³⁺ co-doped CdS.      

Understanding the role of particle size on photophysical properties of CdS:Eu nanocrystals

Here, we report the role of particle size on the photoluminescence (PL) properties of CdS:Eu³⁺ nanocrystals by steady-state and time-resolved PL spectroscopy. It is found that the average decay time 〈τ〉 of undoped CdS nanocrystals increases with increasing the size. The fast component (nanosecond) is assigned due to trapping and slow component (above 10 ns) is due to defect-related emission. The decrease of fast component from 6.6 to 1.32 ns and the slow component from 20 to 14.6 ns of CdS (host) is observed in presence of Eu ions, indicating that the energy transfer occurs from CdS nanoparticles to Eu³⁺ ions. The decay time of Eu³⁺ in CdS shows two decay components (microsecond scale) and we believe that the fast component is attributed to surface-bound Eu³⁺ ions and slow component is due to lattice-bound Eu³⁺ ions. Analysis suggests that PL efficiency of Eu³⁺ ions depends on size of nanoparticles.     

Synthesis and characterization of disodium ethylenediaminetetraacetic acid capped and europium doped CdS nanoparticles

We present a novel two-step chemical synthesis route to produce of disodium ethylenediaminetetraacetic acid (EDTA) capped and europium doped CdS nanoparticles. First EDTA was applied to chelate with cadmium on the surface of cadmium-rich CdS nanoparticles and act as a capping agent. Further, the purified EDTA-capped particles were used to bind with Eu³⁺. The purified and redispersed particles were characterized by UV/vis absorption, photoluminescence, TEM and SEM. It was observed that Eu³⁺ on the nanoparticle surface significantly increased the band gap emission intensity of the CdS nanoparticles.     

Energy transfer from benzoic acid to lanthanide ions in benzoic acid-functionalized lanthanide-doped CaF2 nanoparticles

The preparation of benzoic acid-functionalized CaF₂:Ln³⁺ (Ln = Eu or Tb) nanoparticles and their sensitized luminescence are described in this report. First, to achieve sufficient proof for energy transfer from benzoic acid (BA) to lanthanide ions doped in nanoparticles, we employ Eu³⁺ as the microscopic probe and investigate the luminescent spectra of benzoic acid-functionalized CaF₂:Eu³⁺ (BA-CaF₂:Eu³⁺) nanoparticles. Next, to further reveal the difference between sensitized luminescence and common luminescence for Eu³⁺ doped in CaF₂ nanoparticles, we study the emission spectra of BA-CaF₂:Eu³⁺ nanoparticles excited at 286 nm and 397 nm, respectively. Finally, we analyze and compare the luminescent spectra of BA-CaF₂:Tb³⁺ and CaF₂:Ce³⁺, Tb³⁺ nanoparticles in detail. Our results indicate that both Eu³⁺ and Tb³⁺ doped in CaF₂ nanoparticles can be efficiently sensitized through benzoic acid.     

Probing of surface Eu ions present in ZnO:Eu nanoparticles by covering ZnO:Eu core with Y2O3 shell: Luminescence study

Eu³⁺ doped ZnO nanoparticles are known to have significance extent of surface Eu³⁺ ions due to a large difference in ionic radii. Effect of such Eu³⁺ ions on the luminescence properties of ZnO:Eu nanoparticles has been understood from the luminescence studies of ZnO:Eu nanoparticles covered with Y₂O₃ shell. Based on the asymmetric ratio of luminescence and extent of energy transfer, it is established that when ZnO:Eu nanoparticles are covered with Y₂O₃ shell, a part of Eu³⁺ ions present with ZnO:Eu core migrate to Y₂O₃ shell and occupy Y³⁺ lattice positions.     

Preparation and characterization of nanosized (Y,Bi)VO4:Eu and Y(V,P)O4:Eu red phosphors

Nanosized luminescent (Y,Bi)VO₄:Eu³⁺ and Y(V,P)O₄:Eu³⁺ were synthesized at low temperatures either by a coprecipitation method or by a hydrothermal method from aqueous solutions. The effect of Bi³⁺ ion or P⁵⁺ ion content in the lattice, annealing temperature effects on the crystal structure and the particle size, and the luminescence property of (Y,Bi)VO₄:Eu³⁺ and Y(V,P)O₄:Eu³⁺ nanoparticles were examined with a field-enhanced scanning electron microscopy, XRD, and a spectrofluorometer. The pristine YVO₄:Eu³⁺, (Y,Bi)VO₄:Eu³⁺, or Y(V,P)O₄:Eu³⁺ nanoparticles are 35-50 nm in size. The luminescence spectrum of the Eu³⁺ ion was used to probe its position in the crystal lattice. The dopant ions enter the same lattice sites in the nanocrystalline as in the corresponding bulk material, resulting similar spectral features between them. Photoluminescence intensity is weak for the pristine nanoparticles. Annealing the nanoparticles at temperatures up to 1000 °C results in the increased luminescence intensity (>80% of micrometer-sized phosphors) with the minimal particle growth and the improved particle crystallinity.     

Synthesis and luminescence properties of nanocrystalline Gd2O3:Eu by combustion process

The nanocrystalline Gd₂O₃:Eu³⁺ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 15, and 23 nm for the precursor and samples annealed at 600, 700 and 800 °C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O²⁻-Eu³⁺ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu³⁺ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu³⁺, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu³⁺ ions.     

Charge states of the activator and size effects in BaF2: Eu nanophosphors

ABSTRACT

According to the spectra of stationary X-ray excited luminescence (XEL) of BaF₂: Eu nanophosphors at 80 and 294 K, it was revealed that the thermal annealing of fine-grained nanoparticles (d?=?35?nm) in the range of 400–1000°C, which is accompanied by an increase of their sizes in the range of 58–120?nm, does not result in effective changes of the charge state of Eu^{3 +} → Eu^{2 +} activator, in contrast to CaF₂: Eu nanoparticles. The maximum light output of X-ray excited luminescence of BaF₂: Eu nanophosphors in the 590?nm emission band of Eu³⁺ ion was observed at an annealing temperature of 600°C with the average size of nanoparticles 67?nm. The subsequent growth of annealing temperatures, especially in the range of 800–1000°C, causes decrease in the light output of X-ray excited luminescence due to the increase of defect concentration in the lattice as a result of sharp increase of nanoparticle sizes and their agglomeration. In BaF₂: Eu nanoparticles of 58?nm size, according to the thermostimulated luminescence (TSL) spectrum, transformation of Eu³⁺ → Eu²⁺ under the influence of long-time X-ray irradiation was revealed for the peak of 151?K. Thus, X-ray excited luminescence spectra of BaF₂: Eu nanophosphors are formed predominantly due to the emission of Eu³⁺ ions, while emission of Eu²⁺ ions is observed in the TSL spectra.     

The charge states’ conversion of the activator ions in CaF2:Eu nanophosphors

According to stationary X-ray-excited luminescence spectra and thermally stimulated luminescence spectra of CaF₂:Eu nanophosphors, it was found that Eu³⁺?→?Eu²⁺ conversion can occur during thermal annealing of fine-grained (d?=?25?nm) nanoparticles in the 200–800°C range, which is accompanied by an increase in their size within 40–189?nm. An important role of the exciton mechanism of Eu²⁺ luminescence excitation was revealed according to the temperature dependence of X-ray-excited luminescence spectra of CaF₂:Eu nanoparticles of 114?nm size. The maximum of the X-ray-excited luminescence light output of CaF₂:Eu nanophosphors in the Eu²⁺ ions’ emission band was traced out at 400–500°C annealing temperature and at the size of nanoparticles of 114–180?nm. The subsequent growth of the annealing temperatures, particularly in the 800–1000°C range, causes the reduction of X-ray-excited luminescence light output because of the increment of lattice defects’ concentration due to a sharp increase in the size of nanoparticles and their agglomeration.     

Luminescence studies on lanthanide ions (Eu, Dy and Tb) doped YAG:Ce nano-phosphors

Yttrium aluminum garnet nanoparticles both undoped and doped with lanthanide ions (Ce³⁺, Eu³⁺, Dy³⁺ and Tb³⁺) having average size around 30 (±3 nm) nm were prepared by glycine nitrate combustion method followed by annealing at a relatively low temperature of 800 °C. Increase in the annealing temperature has been found to improve the luminescence intensity and for 1200 °C heated samples there exists strong energy transfer from Tb³⁺ to Ce³⁺ ions in YAG:Ce(2%),Tb(2%) nanoparticles as revealed by luminescence studies. Co-doping the YAG:Ce nanoparticles with Eu³⁺ results in significant decrease in the emission intensity of both Ce³⁺ and Eu³⁺ ions and this has been attributed to the oxidation of Ce³⁺ to Ce⁴⁺ and reduction of Eu³⁺ to Eu²⁺ ions. Dy³⁺ co-doping did not have any effect on the Ce³⁺ emission as there is no energy transfer between Dy³⁺ and Ce³⁺ ions.     

Luminescence studies on ZnO-P2O5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Zinc phosphate glasses doped with Gd₂O₃:Eu nanoparticles and Eu₂O₃ were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P₂O₅ glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu³⁺ ions has been observed when Eu₂O₃ is incorporated in ZnO-P₂O₅ glasses. Lack of energy transfer from these defect centres to Eu³⁺ in Gd₂O₃:Eu nanoparticles doped ZnO-P₂O₅ glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu³⁺ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd₂O₃:Eu nanoparticles or Eu₂O₃ incorporation.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped in Anodise Alumina membrane pores array

Sol–gel template method has been used to prepare BaFBr:Eu²⁺ nanophosphor-SiO₂ hybrid entrapped within the nanopores array (of about 200 nm size) of a comercial anodized alumina (AA) membrane. Structural and morphological measurements using electron microscopy (SEM) and X-ray diffraction (XRD) have shown the presence of the BaFBr:Eu²⁺ nanophosphor in the silica xerogel entrapped within the nanopores array; photoluminescence and X-ray excited luminescence measurements have shown Eu²⁺ luminescence at 395 nm accompanied by a broad band due to AA membrane. The method assures a relatively uniform spreading of the BaFBr nanophosphor into the AA membrane pores array without the nanoparticles agglomeration. Preliminary imaging tests have shown a spatial resolution in the micrometer range and even in the submicrometer range can be expected. As BaFBr:Eu²⁺ is a very efficient X-ray phosphor the material might be used as X-ray micro-imaging detector.     

Probing of inversion symmetry site in Eu-doped GdPO4 by luminescence study: Concentration and annealing effect

Eu³⁺-doped gadolinium orthophosphate (GdPO₄) (Eu³⁺ at%=0, 2, 5, 7, 10, 15, 20 and 30) nanoparticles have been prepared by ethylene glycol route and subsequently heated at 500 and 900 °C. The crystallite size increases with increasing heat-treatment temperature. Luminescence study shows that magnetic dipole transition (⁵D₀→⁷F₁) is prominent over the electric dipole transition (⁵D₀→⁷F₂), which has been attributed to occupancy of inversion symmetry site by more Eu³⁺ ions in Eu³⁺-doped GdPO₄. The luminescence intensity is enhanced as heat-treatment temperature increases from 500 to 900 °C due to the improved crystallinity. Optimum luminescence is observed for 5–7 at% Eu³⁺ in GdPO₄ nanoparticles. Above this concentration, luminescence intensity decreases due to concentration quenching effect. This is supported by lifetime study.     

Red persistent luminescent silicate nanoparticles

Red persistent luminescent diopside nanoparticles doped with Mn²⁺ and codoped with RE³⁺ (Eu²⁺, Dy³⁺) have been obtained by sol-gel method. The influence of codoping rare earth ions on the persistent luminescence was studied by wavelength-resolved thermally stimulated luminescence (TSL) measurements from 30 to 650 K after X-ray irradiation. From these first results, a mechanism of persistent luminescence is proposed. In this mechanism Mn²⁺ and Eu²⁺ act as TSL recombination centers, Mn³⁺ and Eu³⁺ being stable hole centers, whereas Dy³⁺ acts as a good electron trap giving rise to a TSL peak at high temperature. Finally, persistent luminescence was measured. Intensity and persistence of the red luminescence of CaMgSi₂O₆: Mn²⁺–Dy³⁺ are better than those of CaMgSi₂O₆: Mn²⁺ and CaMgSi₂O₆: Mn²⁺–Eu²⁺, which are in agreement with the results of TSL.     

Magnetic nanoparticles trigger cell proliferation arrest of neuro-2a cells and ROS-mediated endoplasmic reticulum stress response

The synthesis, morphological characterization, and optical properties of colloidal, Eu(III) doped Gd₂O₃ nanoparticles with different sizes and shapes are presented. Utilizing wet chemical techniques and various synthesis routes, we were able to obtain spherical, nanodisk, nanotripod, and nanotriangle-like morphology of Gd₂O₃:Eu³⁺ nanoparticles. Various concentrations of Eu³⁺ ions in the crystal matrix of the nanoparticles were tested in order to establish the levels at which the concentration quenching effect is negligible. Based on the luminescence spectra, luminescence lifetimes and optical parameters, which were calculated using the simplified Judd–Ofelt theory, correlations between the Gd₂O₃ nanoparticles morphology and Eu³⁺ ions luminescence were established, and allowed to predict the theoretical maximum quantum efficiency to reach from 61 to 98 %. We have also discussed the impact of the crystal structure of Gd₂O₃ nanoparticles, as well as coordinating environment of luminescent ions located at the surface, on the emission spectra. With the use of a tunable femtosecond laser system and the Z-scan measurement technique, the values of the effective two-photon absorption cross-section in the wavelength range from 550 to 1,200 nm were also calculated. The nonlinear optical measurements revealed maximum multi-photon absorption in the wavelength range from 600 to 750 nm.

     

Preparation and Time-Resolved Luminescence Bioassay Application of Multicolor Luminescent Lanthanide Nanoparticles

Because highly luminescent lanthanide compounds are limited to Eu³⁺ and Tb³⁺ compounds with red (Eu, ~615 nm) and green (Tb, ~545 nm) emission colors, the development and application of time-resolved luminescence bioassay technique using lanthanide-based multicolor luminescent biolabels have rarely been investigated. In this work, a series of lanthanide complexes covalently bound silica nanoparticles with an excitation maximum wavelength at 335 nm and red, orange, yellow and green emission colors has been prepared by co-binding different molar ratios of luminescent Eu³⁺–Tb³⁺ complexes with a ligand N,N,N¹,N¹-(4′-phenyl-2,2′:6′,2′′-terpyridine-6,6′′-diyl)bis(methylenenitrilo) tetrakis (acetic acid) inside the silica nanoparticles. The nanoparticles characterized by transmission electron microscopy and luminescence spectroscopy methods were used for streptavidin labeling, and time-resolved fluoroimmunoassay (TR-FIA) of human prostate-specific antigen (PSA) as well as time-resolved luminescence imaging detection of an environmental pathogen, Giardia lamblia. The results demonstrated the utility of the new multicolor luminescent lanthanide nanoparticles for time-resolved luminescence bioassays.     

Luminescence properties of Tb and Eu-doped alumina films prepared by sol-gel method under various conditions and sensitized luminescence

Rare earth ion (Tb³⁺ and Eu³⁺)-doped alumina films were prepared by the aqueous sol-gel method under various conditions. The influences of the OH groups (phonon relaxation) and rare earth ion concentration (cross-relaxation) on luminescence were examined. In regard to the former relaxation, at treatment temperature above 600°C, reciprocal lifetime decreased with OH concentration, and below 500°C, decreased markedly and nonlinearly. On the other hand, in regard to the latter relaxation, there was negligible effect on luminescence for these doped films. The quantitative treatment was tried to lifetime considering these influences. Tb³⁺ and Eu³⁺ co-doped alumina films showed enhanced Eu³⁺ luminescence by the energy transfer from Tb³⁺ to Eu³⁺. Eu³⁺ luminescence intensity increased with a greater Tb³⁺ concentration.     

Influence of Eu doping content on photoluminescence of Gd2O3:Eu phosphors prepared by liquid-phase reaction method

Europium-doped cubic Gd₂O₃:Eu³⁺ nanoparticles containing various activator content in the range of 5-15 wt% were synthesized by a liquid-phase reaction method to investigate the influence of Eu³⁺ loading on the optical properties of phosphors by using XRD, TEM, BET, spectrometer and fluorometer. The size of Gd₂O₃:Eu³⁺ powders was in the range 21-41 nm. The phosphors showed an initial increase in luminescence and then a subsequent decrease with further doping (above 10 wt%). The decay time was reduced with increasing Eu loading; however, it decreased significantly above the 10% Eu doping. From spectroscopic studies, the Eu³⁺ doping ion distribution was uniform and homogeneous up to the 10 wt% loading because no concentration quenching effect was observed. However, further Eu³⁺ doping above 10 wt% reduced the luminescence due to the concentration quenching effect, as deduced from the shortening of the decay time.