Hydrothermal synthesis and luminescent properties of LaPO4:Eu 3D microstructures with controllable phase and morphology

Three types of Eu³⁺-doped LaPO₄ three-dimensional (3D) microstructures have been hydrothermally prepared by adjusting pH value and the molar ratio of La³⁺ and Eu³⁺ to phosphorus of Na₅P₃O₁₀ (Ln/P) at 180 °C. As the pH value was 0.15 and the molar ratio of Ln/P was in the range of 1/1 to 1/4, 5 μm urchinlike spheres composed of long nanorods of hexagonal LaPO₄:Eu were obtained. As the pH value was 1.00 and the molar ratio of Ln/P was 1/1, 3 μm hollow spheres consisting of short nanorods of monoclinic LaPO₄:Eu were prepared. Keeping the pH value at 1.0 and the molar ratio of Ln/P at 1/4, 6 μm core-shell spheres of monoclinic LaPO₄:Eu formed. Luminescent measurements were performed. Hollow spheres of monoclinic LaPO₄:Eu had the strongest emission intensity. However, the emission intensity of monoclinic core/shell structure was even lower than that of hexagonal LaPO₄:Eu urchinlike spheres.     

Controllable synthesis and luminescence property of CePO4:Tb nanorods

Highly luminescent Tb³⁺-doped CePO₄ with 1D nanostructures were prepared by a simple hydrothermal method. The obtained CePO₄:Tb has a hexagonal or monoclinic structure under different synthetical process. Uniform 1D nanorods with diameters between 40 and 500 nm, and the length ranging from several hundred nanometres to several micrometres were obtained. It is easy to increase the sizes of the samples by adding some CTAB. Results of the XPS show that there is no Ce⁴⁺ in the samples because of the absence of the signal around 917 eV, which is characteristic of Ce⁴⁺. The study of the photoluminescence of Tb³⁺-doped CePO₄ indicates that the luminescent properties of these nanophosphors are strongly dependent on their structures and morphologies.     

Structural phase and morphology control of tetragonal and hexagonal YPO4:Eu nanoflakes for tunable luminescence properties

Eu³⁺-doped tetragonal and hexagonal YPO₄ nanocrystals with different phase structures and morphologies were successfully synthesized by a solvothermal method. It was found that the pH value is a crucial factor in determining the phase structures and their morphologies of YPO₄:Eu nanocrystals. The crystal structure and the properties of the Eu³⁺-doped YPO₄ nanocrystals were characterized by XRD, SEM, TEM, UV–Vis spectroscopy.     

Controllable synthesis and luminescence property of LnPO<Subscript>4</Subscript> (Ln = La,Gd, Y) nanocrystals

Lanthanide orthophosphate LnPO₄ (Ln = La, Gd, Y) nanocrystals with different crystalline structures and morphologies were synthesized successfully by a hydrothermal method under mild conditions. The obtained LaPO₄ have a monoclinic or hexagonal structure with varying the temperature. However, as to GdPO₄ and YPO₄, the temperature has no obvious effect on their structures. By tuning the amount of cetyltrimethylammonium bromide (CTAB), the morphology and size of all samples can be controlled easily and effectively. Noticeably, the structure of YPO₄ can also be controlled by using the CTAB. A systematic study of the photoluminescence in Ln³⁺-doped lanthanide phosphates shows that the luminescent properties of these nanophosphors are strongly dependent on their crystal structures and morphologies.     

Hydrothermal synthesis,characterization and luminescent properties of GdPO4·H2O:Tb nanorods and nanobundles

In this paper, the Tb³⁺-doped GdPO₄·H₂O nanorods and nanobundles have been synthesized by the hydrothermal method with and without glycine, respectively. The X-ray powder diffraction (XRD), thermogravimetric and differential thermal analysis (TG–DTA), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), energy-dispersive spectra (EDS) and photoluminescence (PL) were employed to characterize the as-obtained products. It was found that the addition of glycine and the pH value have crucial influences on the formation of the resulting morphologies and sizes. The possible formation mechanisms for GdPO₄·H₂O:Tb³⁺ nanorods and nanobundles were put forward. A detailed investigation on the photoluminescence of GdPO₄·H₂O:Tb³⁺ different samples revealed that the luminescent properties of products are strongly correlated with the morphologies, sizes, coordination environment and crystal field symmetry.     

Fabrication and characterization of the photoluminescent properties of Tb doped one-dimensional GdPO4 nanorods

In this letter, one-dimensional GdPO₄:Tb³⁺ nanostructures were successfully synthesized by an easy hydrothermal method at 120 °C and 150 °C. Their morphology and structure were characterized and their photoluminescent properties were investigated, including excitation and emission spectra as well as fluorescent dynamics. Results indicated that one-dimensional GdPO₄:Tb³⁺ nanorods formed at low temperature. The hydrothermal temperature did not affect their morphology and size. The crystal structure of GdPO₄:Tb³⁺ nanostructures belongs to monoclinic phase. According to excitation and emission spectra, the strong green emission of Tb³⁺ ions from ⁵D₄-⁷F₅ transitions and the energy transfer from Gd³⁺ to Tb³⁺ ions were observed.     

Synthesis, luminescent, and magnetic properties of LaVO4:Eu nanorods

The LaVO₄:Eu nanorods were synthesized successfully by an ethylenediaminetetraacetic acid (EDTA)-mediated hydrothermal method. The resulting products were characterized using XRD, TEM, HRTEM, Fluorescence Spectrometer and SQUID magnetometer. It was found that Eu³⁺ entered into the LaVO₄ crystalline host lattice and it replaced La³⁺. Consequently the unit cell parameters of LaVO₄:Eu nanorods became smaller. Further studies indicated that the rare earth ions Eu³⁺ improved the properties of the LaVO₄:Eu nanorods evidently. The Eu³⁺ ions doping in LaVO₄ nanorods led to better luminescent properties and magnetic properties than that of pure LaVO₄ nanorods.     

Photoluminescence of Eu3+-doped LaPO4 nanocrystals synthesized by combustion method

Eu³⁺-doped LaPO₄ nanocrystals were synthesized for the first time by a combustion method with urea as a fuel calcined at 700 °C. The diffraction profile of the obtained sample was indexed as a monoclinic monazite-structure by X-ray diffraction (XRD) data. The obtained nanocrystals appeared to be short rod-like with diameters of 5–10 nm and lengths of 20–70 nm. The luminescence intensities of Eu³⁺-doped LaPO₄ nanocrystals were found to be strongly dependent on the quantities of urea added and the concentration of Eu³⁺.     

Characterizations and properties of Eu-doped ZnWO4 prepared via a facile self-propagating combustion method

ZnWO₄ and Eu³⁺-doped ZnWO₄ were prepared for the first time via a facile self-propagating combustion method. The structure, morphology and luminescence of the as-prepared ZnWO₄ and Eu³⁺-doped ZnWO₄ were characterized. The photoluminescent property of Eu³⁺-doped ZnWO₄ complexes indicated an energy transfer from WO₄²⁻ groups to Eu³⁺ and suggested an effective doping of Eu³⁺ into the lattice of ZnWO₄. The photocatalytic activity of ZnWO₄ and Eu³⁺-doped ZnWO₄ was investigated by the photodegradation of rhodamine B (RhB). Eu³⁺-doped ZnWO₄ showed enhanced photocatalytic activity in the photodegradation of RhB.     

Vacuum ultraviolet optical properties of (La,Gd)PO4:RE (RE=Eu, Tb)

Vacuum ultraviolet excitation spectra of phosphors (La,Gd)PO₄:RE³⁺ (RE=Eu or Tb) and X-ray photoelectron spectra of LaPO₄ and GdPO₄ are investigated. The vacuum ultraviolet excitation intensity of (La,Gd)PO₄:RE³⁺ is enhanced with the increasing of Gd³⁺ content, which implies that Gd³⁺ plays an intermediate role in energy transfer from host absorption band to RE³⁺. When Gd³⁺ is doped into LaPO₄:Eu³⁺, charge transfer band (CT band) begins to shift to higher energy region and the overlap degree of CT band and the host absorption band gets greater with more Gd³⁺ doped into LaPO₄. These results suggest that the dopant (Gd³⁺) gives an important influence on energy transfer efficiency. The top of LaPO₄ valance band is formed by the 2p level of O²⁻, whereas that of GdPO₄ valance band is formed by the 2p level of O²⁻ and the 4f level of Gd³⁺, showing the differences in band structures between LaPO₄ and GdPO₄.     

Spectroscopic properties of Eu-doped KLa(PO3)4 and LiLa(PO3)4 powders

KLa(PO₃)₄ (KLP) and LiLa(PO₃)₄ (LLP) doped with different concentrations of Eu³⁺ are grown by solid state reaction. The obtained powders are identified by X-ray diffraction, Raman and FT-IR spectroscopies. These polyphosphates KLa(PO₃)₄ and LiLa(PO₃)₄ crystallize in the monoclinic system but with different space groups respectively P2₁ and C2/c. The evolution of crystal lattice parameters as function of Eu³⁺ concentration in these host lattices was studied. Spectroscopic properties of the Eu³⁺-doped KLa(PO₃)₄ and LiLa(PO₃)₄ at room temperature (RT) are presented. The excitation spectra of the Eu³⁺ ion in condensed polyphosphates along the UV-Visible domain are registered. They show that the position of the charge transfer band (CTB) depends on the host lattices. The effect of structural characteristics of condensed polyphosphates on their optical and colorimetric properties was investigated for the first time. Colorimetric parameters of the Eu³⁺ ions red emission in KLP and LLP are determined and compared with other host matrices. Evolution of colorimetric properties as function of Eu³⁺concentration was discussed.     

Synthesis and luminescent properties of Eu3+ and Dy3+ doped BiPO4 phosphors for near UV-based white LEDs

The phosphors BiPO₄:Eu³⁺ co-doped with Dy³⁺ were synthesized by the conventional solid-state reaction method. XRD and scanning electron microscopy results showed that the crystalline phase of the samples BiPO₄:Eu³⁺ transforms from high-temperature monoclinic phase to low-temperature monoclinic phase with the increase of Dy³⁺ concentration. The photoluminescence properties of the samples showed that the colors shifting from red–orange area to blue–green area are close to those of ideal white light by readjusting the doping concentration ratio of Eu³⁺ and Dy³⁺. The Eu³⁺and Dy³⁺ doped BiPO₄ phosphors may be potential applications in white light near-UV light-emitting diodes.     

Controllable synthesis and luminescence properties of TiO2:Eu3+ nanorods,nanoparticles and submicrospheres by hydrothermal method

Eu³⁺-doped TiO₂ nanocrystals with three kinds of morphologies (nanorods, nanoparticles, and submicrospheres) have been successfully fabricated in cetyltrimethylammonium bromide (CTAB)/water/cyclohexane/n-pentanol reverse micelle by hydrothermal method for the first time and their photoluminescence (PL) properties have also been studied. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), FT-IR, and PL spectra were used to characterize the samples. The acidic and alkaline conditions of the microemulsion play an important role in determining the geometric morphologies of the final products. TiO₂:Eu³⁺ with three different morphologies all exist only in anatase phase and show high luminescence intensity without further calcinations, which show its advantages of energy saving. The shape of emission spectra was independent of the morphologies of the products but the luminescence intensity of the TiO₂:Eu³⁺ materials is strongly dependent on their morphology. The results show that TiO₂:Eu³⁺ nanorods possess the strongest luminescence intensity among the three nanostructured samples.     

Dopant-controlled synthesis of water-soluble hexagonal NaYF<Subscript>4</Subscript> nanorods with efficient upconversion fluorescence for multicolor bioimaging

A novel strategy is proposed to directly synthesize water-soluble hexagonal NaYF₄ nanorods by doping rare-earth ions with large ionic radius (such as La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and Gd³⁺), and the dopantcontrolled growth mechanism is studied. Based on the doping effect, we fabricated water-soluble hexagonal NaYF₄:(Yb,Er)/La and NaYF₄:(Yb,Er)/Ce nanorods, which exhibited much brighter upconversion fluorescence than the corresponding cubic forms. The sizes of the nanorods can be adjusted over a broad range by changing the dopant concentration and reaction time. Furthermore, we successfully demonstrated a novel depth-sensitive multicolor bioimaging for in vivo use by employing the as-synthesized NaYF₄:(Yb,Er)/La nanorods as probes.      

Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> luminescence in calcium and strontium aluminates

Compound CaAl₄O₇ (CA4), SrAl₄O₇ (SA4), CaAl₁₂O₁₉ (CA12) and SrAl₁₂O₁₉ (SA12) have been synthesized by using single step combustion method. The phosphors have been characterized by XRD, SEM and PL techniques. Both CA4 and SA4 possess monoclinic crystal structure whereas CA12 and SA12 possess hexagonal structure. Effects of crystal symmetry on the emission spectrum have been studied by doping the samples with Ce³⁺ and Eu²⁺ ions. The luminescence properties of Ce³⁺ and Eu²⁺ in these hosts is discussed on the basis of their covalent character and the crystal field splitting of the d-orbital of dopant ions. The spectroscopic properties, crystal field splitting, centroid shift, red shift and stokes shift have been studied. Spectroscopic properties of Eu²⁺ ions have been accurately predicted from those of Ce³⁺ ions in the same host. Most importantly experimental results were matched excellently with the calculated results. The preferential substitution of Ce³⁺ and Eu²⁺ at different Ca²⁺, Sr²⁺ crystallographic sites have been discussed. The dependence of emission wavelengths of Ce³⁺ and Eu²⁺ on the local symmetry of different crystallographic sites was also studied by using Van Uitert’s empirical relation. Differences in the emission spectrum of these samples have been observed despite their similar crystal structures and space group. Possible reasons have been discussed.     

Synthesis and photoluminescence properties of Eu-doped γ-Ca3(PO4)2

Eu³⁺-doped (1% and 3%) γ-Ca₃(PO₄)₂ was synthesized by high-pressure and high-temperature experimental method and the samples were characterized by X-ray diffraction. The luminescence properties of samples were investigated by emission and excitation spectra. The excitation spectra of Eu³⁺-doped γ-Ca₃(PO₄)₂ showed that samples were mainly attributed to Eu³⁺–O²⁻ charge-transfer band at 270 nm, and some sharp lines were also attributed to Eu³⁺ f–f transitions in near-UV regions with the strongest peaks at 395 nm. Under the 395 nm excitation, the intense red emission peak at 611 nm was observed. The strongest line (395 nm) in excitation spectra of those phosphors matched well with the output wavelength of UV InGaN-based light-emitting diodes (LEDs) chip. The luminescent properties suggested that Eu³⁺-doped γ-Ca₃(PO₄)₂ might be regarded as a potential red phosphor candidate for near-UV LEDs.     

Luminescence properties of Ca4Y6(SiO4)6O:RE (RE = Eu, Tb, Dy, Sm and Tm) under vacuum ultraviolet excitation

The vacuum ultraviolet excited luminescent properties of Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺ and Tm³⁺ in the matrices of Ca₄Y₆(SiO₄)₆O were investigated. The bands at about 173 nm in the vacuum ultraviolet excited spectra were attributed to host lattice absorption of the matrix Ca₄Y₆(SiO₄)₆O. For Eu³⁺-doped samples, the O²⁻ → Eu³⁺ CTB was identified at 258 nm. Typical 4f-5d absorption bands in the region of 195-300 nm were observed in Tb³⁺-doped samples. For Dy³⁺-doped and Sm³⁺-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm³⁺-doped samples, the O²⁻ → Tm³⁺ CTB was located at 191 nm. About the color purity and emission intensity, Ca₄Y₆(SiO₄)₆O:Tb³⁺ is an attractive candidate of green light PDP phosphor, and Ca₄Y₆(SiO₄)₆O:Dy³⁺ has potential application in the field of mercury-free lamps.     

Low temperature synthesis and photoluminescent properties of CaMoO4:Eu red phosphor with uniform micro-assemblies

Scheelite-type Eu³⁺-doped CaMoO₄ red phosphor with uniform micro-assemblies has been successfully synthesized via a facile hydrothermal method at 120 °C for 10 h. The Eu³⁺-doped CaMoO₄ microstructures were assembled by small nanostructures and the morphology of materials was found to be manipulated by dropping different alkalis into the stock solution for the first time. The structure, morphology, and luminescent property were characterized and investigated by techniques of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). The luminescent investigations confirmed that the Eu³⁺ ions have been effectively doped into CaMoO₄ nanostructures. The successfully achieved Eu³⁺-doped CaMoO₄ nanostructures will be potential in technological applications on near UV chip-based white light emitting diode (WLED).     

Study on preparation and luminescent properties of Eu3+-doped LaAlO3 and GdAlO3

Eu³⁺-doped trigonal LaAlO₃ and orthorhombic GdAlO₃ phosphors have been successfully synthesized by sol–gel method. The crystallization processes of the phosphors have been characterized by X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TG-DSC). The optical properties of these phosphors were investigated using the photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The influences of the different structures and bonding of the hosts on the luminescence performance of Eu³⁺ ion-doped LaAlO₃ and GdAlO₃ were investigated in detail based on chemical bond theory. Under appropriate UV-radiation, the reddish orange light emitted from GdAlO₃:Eu³⁺ was brighter than that from LaAlO₃:Eu³⁺. Such a brightly luminescent phosphor could be considered as an ideal optical material for the development of new optical display systems.     

VUV–UV spectroscopic properties of RE (RE = Ce, Eu and Tb)-doped KMLn(PO4)2 (M = Ca, Sr; Ln = Y, La, Lu)

The VUV excited luminescent properties of Ce³⁺, Eu³⁺ and Tb³⁺ in the matrices of KMLn(PO₄)₂ (M²⁺ = Ca, Sr; Ln³⁺ = Y, La, Lu) were investigated. The bands at about 155 nm in the VUV–UV excitation spectra are attributed to the host lattice absorption, which indicates that the optical band gap of KMLn(PO₄)₂ is about 8.0 eV. Ce³⁺-doped samples show typical Ce³⁺ emission in the range of 300–450 nm, and the energy transfer from host lattice to Ce³⁺ is efficient. For Eu³⁺-doped samples, the O²⁻–Eu³⁺ CTBs are observed to be at about 228 nm except KSrLu(PO₄)₂:Eu³⁺ (247 nm). As for Tb³⁺-doped samples, typical 4f → 5d absorption bands in the region of 175–250 nm were observed.