Emission Spectra Of Eu3 Research Articles

Enhanced hypersensitive (5D0→7F2) transition characteristics of Eu3+ doped β-Ga2O3 microrods

Exploring and realizing the luminescence characteristics of rare earth metal (RE) ions doped gallium oxide (Ga2O3) is crucial for developing optoelectronic device applications. The current research used the solid-state reaction approach to synthesize Ga2O3 microrods doped with various europium (Eu3+) concentrations (0.1, 0.2, 0.3, 0.5, 0.75, and 1 mol). X-ray diffraction (XRD) and Raman spectral analyses confirm the monoclinic structure of β-Ga2O3. The intensity of the Raman phonon modes decreased and a peak shift was observed for Eu:β-Ga2O3. The electron microscopy (SEM, TEM) images depicted a nearly uniform distribution of microrods for undoped and Eu:β-Ga2O3 samples. The interplanar distance (d = 0.290 nm, 0.561 nm, and 0.433 nm), from HR-TEM images, corresponding to (0 0 4), (1 0 0), and (1 0 2) crystallographic orientations confirm the monoclinic structure of β-Ga2O3. The elemental mapping images showed a nearly homogeneous Ga, O, and Eu distribution. The UV–visible diffuse reflectance spectroscopy (UV-DRS) showed a notable reduction in the bandgap as the Eu3+ concentration increased. The emission spectra of Eu: β-Ga2O3 microrods showed a narrow red emission at 612 nm (5D0 → 7F2), which relates to the 5D0 → 7Fj (j = 0, 1, 2, 3) energy level arising from an intra-4f transition of Eu3+ ions upon 394 and 465 nm excitation. The red emission was found to increase with Eu content up to 0.5 mol.%. A quenching of emission due to the multipole–multipole interactions was obtained beyond 0.5 mol.% of Eu. The absolute quantum yield (η) calculated for Eu: β-Ga2O3 (0.5 mol.%) was 3.82 %. The luminescence decay curve using the bi-exponential fit and the average lifetime (τ) of the Eu: β-Ga2O3 (0.5 mol.%) was found to be ∼0.172 ms. CIE chromaticity and correlated color temperature analyses of Eu:β-Ga2O3 microrods yielded a red emission with a superior color purity (93 %). The obtained results suggest that Eu:β-Ga2O3 (0.5 wt.%) microrods could be one of the potential candidates for red light sources.

On the temperature dependent photoluminescence of nanoscale LuPO4:Eu3+ and their application for bioimaging.

This work concerns a synthesis method for efficiently luminescent LuPO4:Eu3+ nanoscale particles (∼100 nm) as well as their temperature (77-500 K) and time dependent photoluminescence. In addition, the incubation of these particles into cells of a human lung adenocarcinomic cell line A549 is briefly presented. This points to the application for bioimaging and detection of cancer cells in the field of medical diagnostics. The emission spectra of Eu3+ doped LuPO4 nanoparticles show four [Xe]4f6 → [Xe]4f6 transition multiplets between 580 and 720 nm, which are typically for Eu3+ comprising luminescent materials, however the most intense one is the 5D0 → 7F4 (696.40 nm, 1.78 eV) transition due to the crystallographic position point symmetry D 2d of Eu3+ in xenotime LuPO4. Such an Eu3+ spectrum is rather useful for diagnostics due to the high penetration depth of 700 nm radiation into tissue.

Innovative approach to tailoring upconversion luminescence in Yb3+/Eu3+ doped CaZrO3 perovskite host matrix

This study presents the synthesis and characterization of upconverter nanostructures consisting of a perovskite host matrix, CaZrO3, co-doped with trivalent ytterbium (Yb3+) and europium (Eu3+), denoted as CaZrO3:Yb3+/Eu3+. Single-doped CaZrO3:Eu3+ samples were excited using a 394 nm UV source, while CaZrO3:Yb3+/Eu3+ samples were excited with a 980 nm diode laser source. Yb3+ ions efficiently absorb the 980 nm light and transfer the absorbed energy to the nearby ion Eu3+ ions, leading to the emission of visible light around 590, 614, and 655 nm, respectively. The emission spectra of Eu3+ ions exhibit an initial increase with increasing Yb3+ concentration, peaking at 7 mol%, followed by a decrease due to luminescence quenching. The decay lifetime of Eu3+ ions under 300 nm excitation decreases simultaneously with increasing Yb3+ concentration, indicating energy migration between Yb3+ and Eu3+. Detailed explanations of the energy transfer mechanism between Yb3+ and Eu3+ ions are provided, supported by equations and diagrams. This study provides valuable insights into the optimization of dopant concentrations for enhancing upconversion luminescence in CaZrO3:Yb3+/Eu3+ nanostructures, with 3 mol% Eu3+ concentration identified as optimal based on preliminary experiments. The findings presented in this paper contribute to the understanding of energy transfer processes in luminescence upconversion materials and highlight the potential of CaZrO3:Yb3+/Eu3+ nanostructures for applications in lighting, displays, and bio-imaging. This work represents a significant advancement in the field of upconversion luminescence emission, particularly in the utilization of CaZrO3 codoped with Yb3+ and Eu3+, and lays the foundation for further research in this area.

Modification of the electronic and optical properties of YVO4:Eu induced by different charge states of the Eu ion

By employing first-principles calculations within the frame of density functional theory, we investigated the modifications of the electronic and optical properties of isolated Eu impurities within YVO4:Eu3+ compound in the presence of additional electron charges. This scenario arises when YVO4:Eu3+ is exposed to gamma radiation that ejects electrons from certain ions and makes them available for capture by others. Our findings reveal that a significant portion of the additional charge is captured by the Eu3+ ion (0.32 e), but this portion is insufficient to confirm a change in the Eu oxidation state from 3+ to 2+. Nevertheless, this capture significantly modifies the Eu electronic configuration, elevating the energy of its occupied 4f-states and bringing them closer to the conduction band bottom. This fact causes the optical absorption of Eu to be generated by 4f → 5d electron transitions, instead of 4f → 4f as in the case of the non-irradiated compound. The presented results qualitatively explain drastic changes in the Eu emission spectrum induced by gamma irradiation of the YVO4:Eu3+, perceived experimentally.

Synthesis and luminescence properties of Eu3+-activated Mg3(PO4)2 phosphors and substitution of phosphate with molybdate, tungstate and sulphate

In the present work, trivalent europium (Eu3+) ion activated Mg3(PO4)2 red phosphors have been synthesized through solid-state reaction method. X-ray diffraction (XRD) confirmed the successful formation of Mg3(PO4)2:Eu3+ phosphors with monoclinic phase with space group P21/c (14). The photoluminescence (PL) spectroscopy was used to record the excitation and emission spectrum of Eu3+ activated Mg3(PO4)2 phosphor. Under the excitation of 395 nm, the resultant samples exhibited the characteristic emissions of Eu3+ ions corresponding to the 5D0 → 7FJ transitions. The optimal doping concentration of Eu3+ ions was determined to be 0.5 mol%. The Commission Internationale de l'Eclairage (CIE) coordinates of Eu3+ activated Mg3(PO4)2 phosphor is calculated, which shows strong red emission. In addition, phosphate group replaced with molybdate, tungstate and sulfate group and found enhancement in emission intensity of prepared phosphors. The obtained results demonstrated that the Eu3+-activated Mg3(PO4)2 phosphors are very appropriate red-emitting phosphors for applications in near-ultraviolet-excited white Light emitting diodes (LEDs).

Web-based application software for Judd-Ofelt analysis of Eu3+ ion luminescence

This article reports on the development of a new Web-based application software for calculating Judd-Ofelt intensity parameters and derived quantities from the emission spectra of Eu3+ doped compounds. The application was entirely developed in JavaScript, and it is compatible with all major browsers. The web application can be accessed via the following link https://sciapps.sci-sim.com/judd_ofelt_analysis_Eu.html. Test samples of ZnO doped with different amounts of Eu3+ were synthesized using the combustion method, and their radiative properties and the chemical environment in the Eu surroundings were thoroughly investigated by Judd-Ofelt intensity and the derived parameters using the online application. In contrast to the tediousness and time-consuming process of these types of calculations, by using this online software, all intensity parameters and the derived quantities can be obtained within a short time.

Monitoring decomposition of Eu3+ doped LaPO4 nanocrystals in glass using Eu3+ as an optical probe for applications in temperature sensing

The methods to directly introduce crystals of known chemistry, size, and optical properties into a glass matrix are useful to circumvent some limitations related to the control of the growth of crystalline phases in glass-ceramics. The emission spectrum of LaPO4:Eu3+ is characteristic for highly symmetrical coordination of Eu3+ and very distinct from the emission spectrum of Eu3+ in amorphous host, which allows for its application as an optical probe. Here, Eu3+ - doped LaPO4 crystals were prepared using solid state reaction and added into various phosphate glass melt before quenching. From the changes in the micro-luminescence spectra, the decomposition occurs along with the diffusion of the Eu3+ ions into the glass confirming that the measurement of the micro-luminescence allows one to precisely track the crystal's decomposition inside the composite. It is demonstrated, for the first time to our knowledge, that the thermometric sensitivity of the Eu3+ ions can be enhanced by adding the LaPO4:Eu3+ crystals into phosphate fluoride glasses due to special separation of the crystallites during the composite preparation and also to the reduction of the self-absorption of the 5D1→7F1 emission. The composite material is promising for applications in temperature sensing.

Optical thermometry based on fluorescence intensity ratio of doped ions and matrix in CaWO4: Eu3+ phosphors

In this work, Eu3+ doped CaWO4 phosphors with various concentrations were obtained by hydrothermal method. XRD and the FE-SEM were used to indicate the structure and morphology of the samples. The temperature-dependent excitation and emission spectra of Eu3+ doped CaWO4 phosphors were measured. Analyzing the test results found that the luminescence of WO42− decreased significantly with the increase of temperature, showing a normal thermal quenching trend, but the luminescence of Eu3+ showed a novel trend of first rising and then decreasing. This novel phenomenon is the result of enhancement of energy transfer effect from the matrix to Eu3+ with temperature increase. The thermal quenching trend of Eu3+ and WO42− luminescence is markedly different. So, the high relative sensitivity is obtained by using FIR of Eu3+ and WO42− to represent temperature. The maximum of relative sensitivity was 3.25% K−1 at 303 K. Meanwhile, the luminescence color of phosphor changed significantly from blue to orange-red with increasing temperature. To sum up, Eu3+ doped CaWO4 phosphor was a potential optical temperature sensing material.

Influence of Tartrate Ligand Coordination over Luminescence Properties of Chiral Lanthanide-Based Metal-Organic Frameworks.

The present work reports on a detailed discussion about the synthesis, characterization, and luminescence properties of three pairs of enantiopure 3D metal-organic frameworks (MOFs) with general formula {[Ln2(L/D-tart)3(H2O)2]·3H2O}n (3D_Ln-L/D, where Ln = Sm(III), Eu(III) or Gd(III), and L/D-tart = L- or D-tartrate), and ten pairs of enantiopure 2D coordination polymers (CPs) with general formula [Ln(L/D-Htart)2(OH)(H2O)2]n (2D_Ln-L/D, where Ln = Y(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III) or Yb(III), and L/D-Htart = hydrogen L- or D-tartrate) based on single-crystal X-ray structures. Enantiopure nature of the samples has been further corroborated by Root Mean Square Deviation (RMSD) as well as by circular dichroism (CD) spectra. Solid-state emission spectra of Eu(III), Tb(III), and Dy(III)-based compounds confirm the occurrence of ligand-to-metal charge transfers in view of the characteristic emissions for these lanthanide ions, and emission decay curves were also recorded to estimate the emission lifetimes for the reported compounds. A complete theoretical study was accomplished to better understand the energy transfers occurring in the Eu-based counterparts, which allows for explaining the different performances of 3D-MOFs and 2D-layered compounds. As inferred from the colorimetric diagrams, emission characteristics of Eu-based 2D CPs depend on the temperature, so their luminescent thermometry has been determined on the basis of a ratiometric analysis between the ligand-centered and Eu-centered emission. Finally, a detailed study of the polarized luminescence intensity emitted by the samples is also accomplished to support the occurrence of chiro-optical activity.

Enhanced luminescence of Eu-doped films based on gap coupled plasmons

Coupled plasmons are promising candidates for enhancing the luminescence, which can drastically alter the electromagnetic environment of emitters and modulate their emission process. In this paper, we have carried out a comparison of enhanced luminescence based on different plasmonic nanostructures and designed a gap coupled structure Au nanorods (NRs)/space layer/Ag nanoparticles (NPs) film to enhance the photoluminescence (PL) of Eu film. The current result indicates that our maximum enhancement factor is 53.5-fold. And our studies reveal that the Ag NPs film as the substrate provides electromagnetic field enhancement, the space layer as the intermediate layer adjusts the distance to decrease the nonradiative energy transfer. A dominant role of the Au NRs in luminescence enhancement is also indicated due to the perfect match between local surface plasmon resonance (LSPR) of Au NRs and the emission spectrum of Eu. Our designed gap coupled nanostructure has multiple plasmon couplings, which can be beneficial to certain applications such as gap coupled plasmonic nanostructure-based detectors and devices.

Dopant concentration induced tuning of emission in Eu3+-doped zirconia nanoparticles

Eu3+-doped zirconia has been considered an efficient phosphor material due to its multi-colour emissive photoluminescence properties. Tuning of emission colour is possible by changing the Eu3+-ions concentration and excitation wavelength. The influence of Eu3+-ions and excitation wavelength on the emission intensity, asymmetric ratio, CIE coordinates, and Judd-Ofelt parameters of the Eu3+-doped zirconia nanophosphors have been explored in this work. Ultra-fine nano-sized particles of pure tetragonal zirconia were observed when the samples were calcined under an argon atmosphere at 800 °C. The expansion and distortion of tetragonal zirconia has been confirmed from XRD and Raman Spectra of Eu3+-doped zirconia samples, respectively. The XPS analysis suggested elemental composition and incorporation of trivalent state of Eu-ions in Eu3+-doped zirconia sample calcined under argon calcination condition. Further, emission spectra of Eu3+-doped zirconia samples have been investigated at the excitation wavelength of 240 nm, 393 nm, and 463 nm. The emission spectra of 3 mol % and 6 mol % Eu3+-doped zirconia samples revealed several emission peaks in the range of 580–710 nm corresponding to the Eu3+-ions transition of 5D0 → 7Fj (=0 to 4). However, due to lower emission intensity, these transitions were not clearly visible up to 1 mol % Eu3+-ions. The CIE coordinates confirmed the tuning of emission colour in Eu3+-doped zirconia nanophosphor at different excitation wavelengths. The Judd-Ofelt parameters also suggested that the Eu3+-doped zirconia may be utilized for better optical gain. So, nano-sized Eu3+-doped zirconia phosphor materials may consider as a potential candidate for different luminescence applications.

Synthesis, properties, luminescence of mixed ligands complexes of acetylsalicylate and 1,10-phenantroline with some light rare earth elements

Mixed ligands complexes of acetylsalicylic and 1,10-phenantroline of Ln(III) with the general formula Ln(AcSa)3(Phen).3H2O (Ln: Nd, Sm, Eu; AcSa-: Acetylsalicylate, Phen: 1,10-phenantroline) have been prepared. The characterization of these complexes have been studied by IR, thermal analysis and mass-spectroscopy methods; The luminescence of complexes was investigated by measuring the excitation and emission spectra. IR spectra suggest that complexes have been synthesised successfully. Mass-spectroscopy showed that the complexes are monomes and they are stable. The intramolecular ligand-to-rare earth energy transfer mechanisms were discussed. The emission spectra of Eu(AcSa)3(Phen).3H2O consist of the 5D0 → 7F2 and 5D0 → 7F1 dominant transitions located at 614 nm and 593 nm, the weaker 5D0 → 7F4 transition located at 699 nm, the weakest 5D0 → 7F3 transition located at 654 nm. The emission spectra of the Sm(AcSa)3(Phen).3H2O displayed three bands, in there, the 4G5/2 – 6H7/2 and 4G5/2 – 6H9/2 equivalent transitions located at 599 nm and 645 nm, the weakest 4G5/2 – 6H5/2 transition located at 564 nm. The emission spectra of the Nd(AcSa)3Phen.3H2O displayed one band at 440 nm, i.e. 4F3/2 – 4I9/2 energy level of Nd3+ was observed. These complexes showed room-temperature photoluminescence

Fabrication and optical properties of Eu3+-doped Ba(Zr, Mg, Ta)O3 transparent fluorescent ceramics

With the development of high-power white light-emitting diodes, transparent ceramics have attracted more and more attention. In this paper, highly transparent Eu-doped Ba(Zr0.16Mg0.28Ta0.56)O3 (Eu3+:BZMT) transparent ceramics with different Eu-doped concentrations were fabricated via a high-temperature solid-state reaction approach. For 1-mm-thickness sample, the in-line transmittance of Eu3+:BZMT transparent ceramics is 72.3% at 650 nm, which is almost 92.3% of the theoretical transmittance. The emission spectrum of Eu3+:BZMT is discovered at 575–650 nm (5D0→7F1 (575–600 nm) and 5D0→7F2 (600–650 nm)), which displays an orange-red emitting. Through the study of the variable temperature spectrum, an outstanding thermal stability has been observed in Eu3+:BZMT. The experiment suggests that Eu3+:BZMT can be potentially adopted as a red phosphor for high-power WLEDs.

Site occupancy and phonon sideband of trivalent europium doped calcium aluminosilicate phosphors

A series of Eu3+ doped Ca2Al2SiO7 were synthesized by the solid-state reaction method. Structural and luminescent properties of the obtained samples were investigated through X-ray diffraction, Raman and luminescence spectra. The luminescent characteristic of the 5D0 → 7F0,1 transitions from emission spectra of Eu3+ ions showed that the Eu3+ ions occupy at two different sites in Ca2Al2SiO7 lattice. The Ca2Al2SiO7:Eu3+ red phosphors have three phonon sidebands with energies ~673 cm−1, 848 cm−1 and 1443 cm−1 which have been determined via the excitation spectra of Eu3+ ions in Ca2Al2SiO7 materials. These obtained phonon energies coincided with the vibrational energies observed from Raman spectra. The multiphonon relaxation rates for the excited levels of 5D1, 5D2 and 5D3 of Eu3+ ions in Ca2Al2SiO7 were also calculated.

Influence of Calcination Temperature on Crystal Growth and Optical Characteristics of Eu3+ Doped ZnO/Zn2SiO4 Composites Fabricated via Simple Thermal Treatment Method

This research paper proposes the usage of a simple thermal treatment method to synthesis the pure and Eu3+ doped ZnO/Zn2SiO4 based composites which undergo calcination process at different temperatures. The effect of calcination temperatures on the structural, morphological, and optical properties of ZnO/Zn2SiO4 based composites have been studied. The XRD analysis shows the existence of two major phases which are ZnO and Zn2SiO4 crystals and supported by the finding in the FT-IR. The FESEM micrograph further confirms the existence of both ZnO and Zn2SiO4 crystal phases, with progress in the calcination temperature around 700–800 °C which affects the existence of the necking-like shape particle. Absorption humps discovered through UV-Vis spectroscopy revealed that at the higher calcination temperature effects for higher absorption intensity while absorption bands can be seen at below 400 nm with dropping of absorption bands at 370–375 nm. Two types of band gap can be seen from the energy band gap analysis which occurs from ZnO crystal and Zn2SiO4 crystal progress. It is also discovered that for Eu3+ doped ZnO/Zn2SiO4 composites, the Zn2SiO4 crystal (5.11–4.71 eV) has a higher band gap compared to the ZnO crystal (3.271–4.07 eV). While, for the photoluminescence study, excited at 400 nm, the emission spectra of Eu3+ doped ZnO/Zn2SiO4 revealed higher emission intensity compared to pure ZnO/Zn2SiO4 with higher calcination temperature exhibit higher emission intensity at 615 nm with 700 °C being the optimum temperature. The emission spectra also show that the calcination temperature contributed to enhancing the emission intensity.

Temperature-induced solvent assisted single-crystal-to-single-crystal transformation of Mg(II)-Ln(III) heterometallic coordination polymers

Two new heterometallic coordination polymers (CPs) [Ln2 (pydc)6Mg3(H2O)6]·11H2O (Ln ​= ​Eu (1), Tb (2); H2pydc ​= ​pyridine-2,6-dicarbolylic acid) were synthesized by solvothermal method at 120 ​°C in 48 ​h. Interestingly, after being left in the mother liquor for 3 days at room temperature, the crystal structures of the coordination polymers transform into anionic complexes 2 [Mg(H2O)6]·2 [Ln (pydc)3]·2Him·im•8H2O (Ln ​= ​Eu (3), Tb (4); im ​= ​imidazole; Him ​= ​protonated imidazole) by single-crystal-to-single-crystal transformation. The four complexes were characterized by elemental analysis, IR, TG, XRD as well as single-crystal X-ray diffraction. Coordination polymers 1 and 2 exhibit three-dimensional network structure and their topology symbol is {44.62}3{49.66}2, whereas complexes 3 and 4 are zero dimensional molecules. The luminescence properties of the complexes were determined at solid state. They show characteristic emission spectra of Eu(III) and Tb(III) ions, respectively. The quantum yield Фtotal is 48.42 ​± ​10%, 95.65 ​± ​10%, 44.22 ​± ​10%, and 76.97 ​± ​10% for coordination polymers 1 (Mg–Eu), 2 (Mg–Tb), 3 (Mg–Eu), and 4 (Mg–Tb), respectively. The corresponding fluorescence decay lifetime of 1–4 is τobs1 ​= ​1884.72 ​± ​1.51, 1777.75 ​± ​1.45, 1625.17 ​± ​1.40, and 1487.75 ​± ​1.36 ​μs? The effect of Mg(II) on the fluorescence properties of the lanthanide coordination polymers was investigated.

Highly Luminescent and Anti-Photobleaching Core-Shell Structure of Mesoporous Silica and Phosphatidylcholine Modified Superparamagnetic Iron Oxide Nanoparticles.

Highly fluorescent magnetic nanoparticles (Eu(TTA)3(P(Oct)3)3@mSiO2@SPION) [europium (III) chloride hexahydrate = Eu; 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione = TTA; trioctylphosphine = (P(Oct)3); mesoporous silica = mSiO2; superparamagnetic iron oxide nanoparticle = SPION] were developed as a dual-functional imaging agent. The hierarchical structure was composed of a magnetic core and mesoporous silica shell was constructed using a cationic surfactant template after coating with phosphatidylcholine of oleic acid coated SPION. Afterward, the surface and cavities of mSiO2@SPION were modified with 3-(trimethoxysilyl) propyl methacrylate (TMSPMA) as a silane coupling agent to introduce methacrylate groups. Eu(TTA)3(P(Oct)3)3 molecules are penetrated, located and bonded covalently inside of the cavities/mesopores of mSiO2, it shows extremely stable anti-photobleaching properties. The emission spectra of Eu(TTA)3(P(Oct)3)3@mSiO2@SPION indicated typical hypersensitivity transition 5D0→7F2 at 621 nm. The concentration of Eu(TTA)3(P(Oct)3)3@mSiO2@SPION was varied between 10 and 500 μL/mL to evaluate the cytotoxicity with NCI-H460 (H460) cells using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. In addition, the presence of a strong red-emitting Eu(TTA)3(P(Oct)3)3@mSiO2@SPION in the cytoplasm was observed by fluorescence microscopy. Those results that it can be a potential candidate for dual-functional contrast agent and PL nanomaterials for fabricating the diagnostic kits to amplify the low signal.

Cathodoluminescence of organo-lanthanide complexes

The cathodoluminescence (CL) of organo-lanthanide complexes is studied as a modeling of beta luminescence. It is found that complexes of Sc, La, and lanthanides with anionic ÔO, ÔN bidentate and O-monodentate ligands under excitation by fast electrons display luminescence of various intensities. In the spectra of Sc, La, Nd, Er, and Tm compounds, only broadened bands of the ligands peaked about 450 nm are observed. A similar spectrum gives anthracene, which is used as a reference compound. In contrast, the emission spectra of Eu and Tb compounds contain only the narrow bands of f–f transitions characteristic of these metals. The spectra of Sm, Dy, and Yb derivatives exhibit both the bands of ligands and weak metal-centered luminescence. X-ray luminescence (RL) of several terbium complexes is also investigated. A comparison of the photoluminescence, CL and RL spectra of the studied compounds reveals a similarity of the shape of the spectra but a significant difference in their intensities. Terbium compounds show record scintillating activity. Possible mechanisms of luminescence of organo-lanthanide complexes upon different types of excitation are discussed.

Energy transfer and luminescent properties of Eu3+, Tb3+, Eu3+-Yb3+and Tb3+-Yb3+ doped α-NaYF4 nanophosphors prepared by coprecipitation route

Cubic α-NaYF4 nanometer-sized crystals doped with Eu3+, Tb3+, Yb3+-Eu3+ or Yb3+-Tb3+ were synthesized by an original coprecipitation route. The obtained nanoparticles exhibited primary particles showing cubic shape with sizes ranging between 35 and 65 nm. The singly- or co-doped nanophosphors exhibited strong red (Eu3+) or green (Tb3+) fluorescence upon ultraviolet (UV) or near infrared (NIR) excitation, which resulted respectively from down- or up-conversion processes occurring in their structure. Spectroscopic properties were investigated on the basis of emission spectra as well as luminescence decays. From the emission spectra of Eu3+ doped samples, the Ω2 and Ω4 Judd-Ofelt intensity parameters were calculated. The concentration quenching of the Eu3+ or Tb3+ ion emissions in singly-doped or Yb3+ co-doped α-NaYF4 were ascribed to resonant cross-relaxations. The main derived interaction between the active ions was evidenced as an electric dipole-dipole one through fitting the decays curves with the Inokuti-Hirayama model. The critical distances and energy transfer microparameters for the transfer processes were given showing very short range interaction. The dependence of integral up-conversion intensity on the NIR energy of the beam power was measured. The results indicated a two-photon process based on a cooperative energy transfer.

Bright red luminescence emission of macroporous honeycomb-like Eu3+ ion-doped ZnO nanoparticles developed by gel-combustion technique

The impact of europium (Eu3+) ion doping has been outlined in improving the structure and optical properties of macroporous honeycomb-like zinc oxide (ZnO) nanoparticles, produced by the gel-combustion technique by changing the quantity of dopant. The X-ray diffraction (XRD) research verified that the hexagonal wurtzite structure of ZnO was not disturbed by Eu3+ substitution. Scherrer method, Scherrer plots (SP), Williamson-Hall (W–H) plots and Size-Strain plots (SSP) were used to estimate the crystallite size. Decreased crystallite size in ZnO:Eu3+ was noticed along with lower angle shift of XRD peaks and increased lattice parameters such as unit cell volume that can be described as replacement result of Eu3+ at Zn sites. Fourier transform infrared (FTIR) spectroscopy analysis confirmed the Eu3+ dopant by moving the peak from 474 cm−1 to 525 cm−1. Field-emission scanning electron microscopy (FESEM) pictures verified macroporous honeycomb-like structures. UV–Visible (UV–Vis) absorption spectroscopic studies show that the ability of ZnO:Eu3+ nanoparticles concerning the absorption of visible light increased upon Eu3+ doping with a red shift compared to ZnO nanoparticles. Photoluminescence (PL) emission spectra of Eu3+ doped ZnO nanoparticles exhibited five intense band emissions at 579, 591, 617, 652, and 706 nm ascribed to 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4 transitions of Eu3+ ions when excited at 465 nm wavelength, originated from intra-4f transition of Eu3+ ions, respectively. ZnO:Eu3+ nanoparticles intensified with concentration progression and revealed as nanoparticles emitting red under 465 nm excitation.