Synthesis,characterization and formation mechanism of monodispersed Gd<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Eu<Superscript>3+</Superscript> nanocrystals

Monodispersed Gd₂O₂S:Eu³⁺ nanostructures with tunable morphologies have been selectively fabricated by solvothermal method in the presence of stable inorganic precursors avoiding metalorganic precursors. The size and morphology of the products were controlled successfully by adjusting the reaction conditions. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). The corresponding UV absorption and photoluminescence excitation spectra show a significant blue-shift confirming the quantum confinement effect. A possible growth mechanism for the formation of monodispersed Gd₂O₂S:Eu³⁺ nanocrystals has been proposed. The luminescence mechanism and the size dependence of their fluorescence properties are also discussed.     

Controlled synthesis, formation mechanism and lumincence properties of novel 3-dimensional Gd2(MoO4)3:Eu3+ nanostructures

Orthorhombic Gd₂(MoO₄)₃:Eu³⁺ nanosized particles with complex 3D self-assembled superstructures (dumbbell) were successfully synthesized by a hydrothermal method in ethyleneiamine tetra-acetic acid (EDTA) mediated processes. The pH value, reaction time, temperature, ando molybdenum source have crucial influence on the growth mechanism, shape evolution, and nanostructures. In the hydrothermal process, EDTA not only acts as a chelating reagent to facilitate the formation of Gd₂(MoO₄)₃:Eu³⁺, but also acts as a surface capping agent to adhere to the newly created surface and to promote the crystal splitting. Comprehensive structural, morphological studies like X-ray diffraction, scanning and transmission electron microscopy were employed to characterize the as synthesized nanostructures. Photoluminescence studies on Gd₂(MoO₄)₃:Eu³⁺ showed strong red emission upon UV illumination, and this implied potential application in the field of luminescent nano ceramics.     

Luminescence properties of Nd-doped (Y,Gd)BO3 phosphors

A system of 0.03 mol Nd³⁺-doped (Y,Gd)BO₃ phosphors were prepared by the conventional solid state reaction method for different concentrations of Gd³⁺ ions and were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and NIR emission measurements. The emitted radiation was dominated by 1057 nm peak in the NIR region as a result of ⁴F_3/2 → ⁴I_11/2 transitions of Nd³⁺ ions. As the concentration of Gd³⁺ ions increases from 0.00 to 0.57 mol, the grain sizes and the intensity of NIR emission peaks were improved. The results are discussed in comparison with similar reported works.     

Hydrothermal synthesis and photoluminescence properties of Gd2Zr2O7:Tb phosphors

This paper presents hydrothermal synthesis, characterization, and photoluminescence (PL) properties of novel green-emitting phosphors, Gd₂Zr₂O₇:Tb³⁺. Their crystal structure, morphology and photoluminescence properties were investigated by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM) and fluorescence spectrophotometer. The results revealed that one-dimensional Gd₂Zr₂O₇:Tb³⁺ nanorods with diameter of about 30 nm and length of 150-300 nm were formed, and the products exhibited a fluorite-type structure. PL study revealed that Gd₂Zr₂O₇:Tb³⁺ phosphors presented dominant green emission luminescence, which was attributed to the transitions from ⁵D₄ excited states to ⁷F_J (J = 3-6) ground states of Tb³⁺. The luminescence intensity of Gd₂Zr₂O₇:Tb³⁺ with different Tb³⁺ concentration was also investigated and reported, and an obvious concentration quenching was observed when Tb³⁺ ion concentration was 5 at.%.     

Electrospinning preparation of LaOBr:Tb3+ nanostructures and their photoluminescence properties

Tb³⁺-doped LaOBr nanostructures including nanofibers, nanobelts, and hollow nanofibers were synthesized for the first time via calcinating the electrospun polyvinyl pyrrolidone/[La(NO₃)₃ + Tb(NO₃)₃ + NH₄Br] composites. X-ray diffraction analysis revealed that LaOBr:Tb³⁺ nanostructures are tetragonal in structure with space group of P4/nmm. The morphologies and sizes of LaOBr:Tb³⁺ nanostructures were investigated using scanning electron microscope and transmission electron microscope. Under the excitation of 254-nm ultraviolet light, LaOBr:Tb³⁺ nanostructures exhibit the green emissions of predominant peak at 543 nm, which is ascribed to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. It is found that the optimum doping concentration of Tb³⁺ ions in the LaOBr:Tb³⁺ nanofibers is 3 %. Interestingly, we found that the luminescence intensity of hollow nanofibers is obviously greater than that of nanofibers and nanobelts for LaOBr:Tb³⁺ under the same measuring conditions. Moreover, the luminescence of LaOBr:Tb³⁺ nanostructures are located in the green region in Commission Internationale de L’Eclairage chromaticity coordinates diagram. The formation mechanisms of LaOBr:Tb³⁺ nanofibers, nanobelts, and hollow nanofibers were also proposed. LaOBr:Tb³⁺ nanostructures are promising nanomaterials for applications in the fields of light display systems and optoelectronic devices.     

Shape-selective synthesis and opto-electronic properties of Eu<Superscript>3+</Superscript>-doped gadolinium oxysulfide nanostructures

A simple and facile hydrothermal route has been demonstrated for the shape-selective preparation of highly crystalline Gd₂O₂S:Eu³⁺ nanostructures, such as nanocrystals/nanoplates, nanosheets, nanobelts, nanotubes, nanorods, and nanowires are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), photoluminescence (PL) techniques. The as-prepared samples are characterized using X-ray photoelectron spectra (XPS), to investigate the elementary states on the surfaces. The concentration of precursor chemicals, pH, the reaction time, and the temperature are important factors in the morphological control of Gd₂O₂S:Eu³⁺ nanostructures. The adjustment of these parameters can lead to an obvious shape evolution of products. The origin and nature of the opto-electronic transitions were observed using opto-impedance measurements. An erratum to this article can be found at     

Preparation of highly ordered growth of single-crystalline Gd2O2S:Eu nanostructures

A simple and facile template-assisted hydrothermal route has been demonstrated for the shape-selective preparation of highly ordered single-crystalline Gd₂O₂S:Eu³⁺ nanostructures, such as nanotubes, nanorods and nanoflowers. These fabricated nanostructures possess desirable atomic structures, surfaces, morphologies and properties to meet the growing demands and specific requirements of new technologies. The concentration of precursor chemicals, the temperature, the reaction time, and the use of a capping agent are key factors in the morphological control of Gd₂O₂S:Eu³⁺ nanostructures. The morphology and the phase composition of the prepared nanostructures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy disperse spectroscopy (EDS) and photoluminescence (PL). We believe this technique will be readily adopted in realizing other forms of various nanostructured materials.     

Study of the relationship between crystal structure and luminescence in rare-earth-implanted Ga2O3 nanowires during annealing treatments

A systematical analysis of the correlation between the crystalline quality and the luminescence of rare-earth-implanted β-Ga₂O₃ nanostructures with potential applications in visible and ultraviolet photonics is presented. Europium ions led to red emission while gadolinium ions are efficient ultraviolet emitters. Different degrees of lattice recoveries of the nanostructures have been achieved after implantation by rapid thermal annealing treatments carried out at different temperatures. The recovery process has been analyzed by transmission electron microscopy (TEM), high-resolution TEM, and Raman techniques. High-fluence implantation with either of the two rare earth ions induces partial amorphization of the structures. Partial recrystallization of the nanostructures above 500 °C is revealed by Raman analysis. Nearly complete recovery of the crystal structure is obtained in the annealing temperature range 900–1100 °C, coincident with the expected value for bulk Ga₂O₃. Cathodoluminescence and photoluminescence allowed comparison of the Eu³⁺ and Gd³⁺ intraionic luminescence lines after annealing at different temperatures and their correlation with the crystallinity. It has been found that the width of the Eu³⁺ luminescence lines clearly correlates with the width of the Raman peaks, both decreasing with annealing temperature, which shows the possibility of using the luminescence of this rare earth as a probe for lattice disorder. On the other hand, our results suggest that Gd³⁺ lines are much less sensitive to disorder.     

NIR-excited NIR and visible luminescent properties of amphipathic YVO<Subscript>4</Subscript>: Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> nanoparticles

This article reports the luminescence properties of amphipathic YVO₄:Er³⁺/Yb³⁺ nanoparticles (average grain size ca. 20 nm) obtained by an oleate-aided hydrothermal process. Depending on the upconversion (UPC) and downconversion (DWC) processes, they show luminescence in the visible and near-infrared (NIR) regions, respectively, by 980-nm excitation. The sample doped with Er³⁺:2.5 mol% and Yb³⁺:10 mol% showed the highest luminescence intensity in both the visible and NIR regions as a result of efficient energy transfer from Yb³⁺ to Er³⁺ ions. The hydrothermal treatment greatly enhanced both the DWC and UPC luminescence efficiencies. This is due to the reduction in the concentration of surface defects and ligands, accompanied by grain growth. NIR Fluorescence microscopy revealed for the first time that DWC luminescence is sufficiently intense for application of these nanocrystals as a NIR bioprobe.     

Synthesis and photoluminescence study of narrow-band UVB-emitting LiSr<Subscript>4</Subscript>(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>:Gd<Superscript>3+</Superscript>, Pr<Superscript>3+</Superscript> phosphor

A series of Pr³⁺, Gd³⁺ and Pr³⁺–Gd³⁺-doped inorganic borate phosphors LiSr₄(BO₃)₃ were successfully synthesized by a modified solid-state diffusion method. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. Surface morphology of the sample was studied by scanning electronic microscopy (SEM). The optimal concentrations of dopant Gd³⁺ ions in compound LiSr₄(BO₃)₃ were determined through the measurements of photoluminescence (PL) spectra of phosphors. Gd³⁺-doped phosphors LiSr₄(BO₃)₃ show strong band absorption in UV spectral region and narrow-band UVB emission under the excitation of 276 nm was only due to ⁶P _J → ⁸S_7/2 transition of Gd³⁺ ions. The effect of Pr³⁺ ion on excitation of LiSr₄(BO₃)₃:Gd³⁺ was also studied. The excitation of LiSr₄(BO₃)₃:Gd³⁺, Pr³⁺ gives a broad-band spectra, which show very good overlap with the Hg 253.7 nm line. The photoluminescence spectra of LiSr₄(BO₃)₃ with different doping concentrations Pr³⁺ and keeping the concentration of Gd³⁺ constant at 0.03 mol have also been studied. The emission intensity of LiSr₄(BO₃)₃:Pr³⁺–Gd³⁺ phosphors increases with increasing Pr³⁺ doping concentration and reaches a maximum at 0.01 mol. From the photoluminescence study of LiSr₄(BO₃)₃:Gd³⁺, Pr³⁺ we conclude that there was efficient energy transfer from Pr³⁺→ Gd³⁺ ions in LiSr_4?x?y Pr _x Gd _y (BO₃)₃ phosphors.     

Visible quantum cutting through downconversion in Eu3+-doped K2GdZr(PO4)3 phosphor

K₂Gd_1?xZr(PO₄)₃:Eu_x³⁺ (0.02 ≤ x ≤ 0.1, x is in mol.%) were prepared by solid-state reaction method and their photoluminescence properties were investigated in ultra-violet (UV) and vacuum ultra-violet (VUV) region. The phenomenon of visible quantum cutting through downconversion was observed for the Gd³⁺–Eu³⁺ couple in this Eu³⁺-doped K₂GdZr(PO₄)₃ system. Visible quantum cutting, the emission of two visible light photons per absorbed VUV photon, occurred upon the 186 nm excitation of Gd³⁺ at the ⁶G_J level via two-step energy transfer from Gd³⁺ to Eu³⁺ by cross-relaxation and sequential transfer of the remaining excitation energy. The results revealed that the efficiency of the energy transfer process from Gd³⁺ to Eu³⁺ in the Eu³⁺-doped K₂GdZr(PO₄)₃ system could reach to 155% and K₂GdZr(PO₄)₃:Eu³⁺ was effective quantum cutting material.     

A novel strategy to synthesize Gd2O2S:Eu3+ luminescent nanobelts via inheriting the morphology of precursor

Gd₂O₃:Eu³⁺ nanobelts were fabricated by calcination of the electrospun PVP/[Gd(NO₃)₃ + Eu(NO₃)₃] composite nanobelts. For the first time, Gd₂O₂S:Eu³⁺ nanobelts were successfully prepared via inheriting the morphology and sulfurization of the as-prepared Gd₂O₃:Eu³⁺ nanobelts precursor using sulfur powders as sulfur source by a double-crucible method we newly proposed. X-ray diffraction analysis indicated that Gd₂O₂S:Eu³⁺ nanobelts were pure hexagonal in structure with space group P \( \bar{3} \) m1. Scanning electron microscope analysis results showed that the width and thickness of the Gd₂O₂S:Eu³⁺ nanobelts were ca. 2.1 μm and 129 nm, respectively. Under the excitation of 330-nm ultraviolet light, Gd₂O₂S:Eu³⁺ nanobelts emitted red emissions of predominant peaks at 628 and 618 nm which were attributed to the ⁵D₀ → ⁷F₂ energy levels transitions of the Eu³⁺ ions. It was found that the optimum doping molar concentration of Eu³⁺ ions in Gd₂O₂S:Eu³⁺ nanobelts was 5 %. Possible formation and sulfurization mechanisms of Gd₂O₂S:Eu³⁺ nanobelts were also proposed. This new sulfurization technique is of great importance, not only can inherit the morphology of rare earth oxides, but also can fabricate pure-phase rare earth oxysulfides at low temperature compared with conventional sulfurization method.     

Luminescence properties and gamma-ray response of the Ce and Ca co-doped (Gd,Y)F3 single crystals

The Ca0.5% and Ce1%, 3%, 7%, 10% co-doped Gd_0.5Y_0.5F₃ single crystals were grown by the μ-PD method. In the Ca0.5% and Ce3% co-doped sample, Ce³⁺-perturbed luminescence at 380 nm was observed with 32.4 ns photoluminescence decay time. The energy transfer in the sequence of the regular Ce³⁺→ (Gd³⁺)_n→ the perturbed Ce³⁺ sites was evidenced through observation of decay time shortening of the regular Ce³⁺ and Gd³⁺ centers and the change between the Gd³⁺ and Ce³⁺-perturbed emission intensity. The gamma-ray excited scintillation response of the Ca0.5%, Ce7% co-doped Gd_0.5Y_0.5F₃ sample was investigated with the help of the pulse height spectra and the light yield, energy resolution and non-proportionality was evaluated in the interval of energies of 59.4-1274 keV.     

Gd induced the variations of anti-site defect and magnetism in the double perovskite oxides Sr2FeMoO6

Crystal structure, magnetic and transport properties of Sr_2−xGd_xFeMoO₆ (0 ≤ x ≤ 0.25) are investigated. The anti-site defect in this series can be adjusted by rare-earth element of Gd. Gd³⁺ replace for Sr²⁺ results in the increase of anti-site defect due to the differences in valence and size between Gd³⁺ and Sr²⁺. The moment of Gd³⁺ may be in canted structure. The effective moment of Gd³⁺ is about 1.5 μ_B/Gd³⁺, which is anti-parallel to that of Fe³⁺. The moment of Gd³⁺, Fe³⁺, and Mo⁵⁺/Mo⁴⁺ interact each other, and play important roles on transport and magnetic properties.     

One-pot synthesis and strong near-infrared upconversion luminescence of poly(acrylic acid)-functionalized YF<Subscript>3</Subscript>:Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript> nanocrystals

This paper describes the synthesis of new upconverting luminescent nanoparticles that consist of YF₃:Yb³⁺/Er³⁺ functionalized with poly(acrylic acid) (PAA). Unlike the upconverting nanocrystals previously reported in the literature that emit visible (blue-green-red) upconversion fluorescence, these as-prepared nanoparticles emit strong near-infrared (NIR, 831 nm) upconversion luminescence under 980 nm excitation. Scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction were used to characterize the size and composition of the luminescent nanocrystals. Their average diameter was about 50 nm. The presence of the PAA coating was confirmed by infrared spectroscopy. The particles are highly dispersible in aqueous solution due to the presence of carboxylate groups in the PAA coating. By carrying out the synthesis in the absence of PAA, YF₃:Yb³⁺/Er³⁺ nanorice materials were obtained. These nanorice particles are larger (∼700 nm in length) than the PAA-functionalized nanoparticles and show strong typical visible red (668 nm), rather than NIR (831 nm), upconversion fluorescence. The new PAA-coated luminescent nanoparticles have the pottential be used in a variety of bioanalytical and medical assays involving luminescence detection and fluorescence imaging, especially in vivo fluorescence imaging, due to the deep penetration of NIR radiation.      

Synthesis and luminescence of ultrafine Er3+- and Yb3+-doped Gd11SiP3O26 and Gd14B6Ge2O34 particles for cancer diagnostics

In search of new contrast materials for NMR and fluorescence diagnostics and neutron capture therapy of cancer, we have synthesized ultrafine Er³⁺- and Yb³⁺-doped Gd₁₁SiP₃O₂₆ and Gd₁₄B₆Ge₂O₃₄ particles and studied their luminescence properties. We measured the Er³⁺ upconversion luminescence spectra of the gadolinium erbium ytterbium phosphosilicates and borate germanates in the visible range and evaluated the absolute quantum yield of their luminescence. The quantum yield of luminescence in the gadolinium phosphosilicate Gd₁₁SiP₃O₂₆ doped with 5.0 at % Yb and 2.5 at % Er is comparable to that in known Yb³⁺/Er³⁺ codoped fluorides. The nonradiative Yb³⁺ ?? Er³⁺ energy transfer efficiency is evaluated.     

Synthesis and photoluminescent properties of Gd3O4Br:Er phosphors prepared by solid-state reaction method

Pure orthorhombic Gd₃O₄Br:Er³⁺ upconversion phosphors were synthesized by a solid-state reaction method and the structural properties of Gd₃O₄Br:Er³⁺ were investigated by X-ray diffraction; field emission scanning electron microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The results show that Gd₃O₄Br has low phonon cutoff energy, indicating that Gd₃O₄Br:Er³⁺may have high luminescent efficiency. Intense green (514–582 nm) and strong red (645–692 nm) upconverted luminescence of Gd₃O₄Br:Er³⁺ were observed under 980 nm laser excitation. The bright green emission is visible to the naked eyes even for 1 mW of the pump power (980 nm) for Gd₃O₄Br:Er³⁺ (0.1%) samples, indicating that Gd₃O₄Br:Er³⁺ may be used as upconversion phosphors.     

Ultraviolet upconversion luminescence of Gd3+ and Eu3+ in nano-structured glass ceramics

Ultraviolet multiphoton upconversion emissions of Eu³⁺ (⁵H_3–7, ⁵G_2–6, ⁵L₆ → ⁷F₀) and Gd³⁺ (⁶I_J, ⁶P_J → ⁸S_7/2) are studied in the Eu³⁺ (or Gd³⁺) doped SiO₂–Al₂O₃–NaF–YF₃ precursor glasses and glass ceramics containing β-YF₃ nanocrystals, under continuous-wavelength 976 nm laser pumping. It is experimentally demonstrated that energy transfer from Yb³⁺ to Tm³⁺, then further to Eu³⁺ or Gd³⁺ is responsible for the upconversion process. Compared to those in the precursor glasses, the upconversion emission intensities in the glass ceramics are greatly enhanced, owing to the participation of rare earth ions into the low-phonon-energy environment of β-YF₃ nanocrystals. Hopefully, the studied glass ceramics may find potential applications in the field of ultraviolet solid-state lasers.     

Luminescence of SrGdGa3O7:RE(RE = Eu, Tb) phosphors and energy transfer from Gd to RE

Eu³⁺- and Tb³⁺-activated SrGdGa₃O₇ phosphors were synthesized by the solid-state reaction and their luminescence properties were investigated. Sr(Gd_1 − xEu_x)Ga₃O₇ and Sr(Gd_1 − xTb_x)Ga₃O₇ formed continuous solid solution in the range of x = 0-1.0. Unactivated SrGdGa₃O₇ exhibited a typical characteristic excitation and emission of Gd ion. The SrGdGa₃O₇:xEu³⁺ and SrGdGa₃O₇:xTb³⁺ phosphors also showed the well-known Eu³⁺ and Tb³⁺ excitation and emission. The energy transfer from Gd³⁺ to Eu³⁺ and Tb³⁺ were verified by photoluminescence spectra. The dependence of photoluminescence intensity on Eu³⁺ and Tb³⁺ concentration were also studied in detail and the photoluminescence (PL) intensity of SrGdGa₃O₇:Eu and SrGdGa₃O₇:Tb were compared with commercial phosphors, Y₂O₃:Eu and LaPO₄:Ce,Tb. The luminescence decay measurements showed that the lifetimes of Eu³⁺ and Tb³⁺ were in the range of microsecond. The energy transfer from Gd³⁺ to Tb³⁺ was also observed in decay curve.     

Energy transfer and radiative recombination processes in (Gd, Lu)3Ga3Al2O12:Pr3+ scintillators

(Gd_xLu_3−x)Ga₃Al₂O₁₂:0.3 at.%Pr (x = 0.025, 0.05, 0.1, 0.2, 0.4, 0.6) (GLGAG:Pr) polycrystalline powders are prepared by solid-state reaction method. To better understand the luminescence mechanism, the optical diffuse reflectance, photoluminescence emission and excitation, X-ray excited luminescence spectra and decay kinetics of GLGAG:Pr were investigated in detailed, allowing the determination of energy transfer from 5d state of Pr³⁺ to 4f state of Gd³⁺, and the non-radiative relaxation from 5d to 4f state of Pr³⁺. Besides, the former process plays more negative role in the emission quenching of GLGAG:Pr than later one. Pr³⁺ ion is regarded as an ineffective activation ion in Gd-based multicomponent aluminate garnets. In addition, the wavelength-resolved thermoluminescence spectra of GLGAG:Pr were studied after UV and X-ray irradiation. It is revealed that the localized recombination processes from electron traps to lower lying 4f levels of Pr³⁺ occurs without populating the higher 5d levels of Pr³⁺.