Synthesis and phosphorescence properties of Mn, La and Ho in MgAl2Si2O8

Mn⁴⁺, La³⁺ and Ho³⁺ doped MgAl₂Si₂O₈-based phosphors were first synthesized by solid state reaction. They were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray powder diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). The phosphors were obtained at about 1300 °C. They showed broad red and fuchsia-pink emission bands in the range of 610-715 nm and had a different maximum intensity when activated by UV illumination. Such a fuchsia-pink emission can be attributed to the intrinsic d-d transitions of Mn⁴⁺.     

Synthesis and luminescence properties of Bi-doped YVO4 phosphors

YVO₄:Bi³⁺ phosphors have been prepared by a convenient high-temperature solid-state method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) technologies are used to study the luminescence properties of YVO₄:Bi³⁺ phosphors. The emission and excitation spectra of Bi³⁺ in the YVO₄ lattice have been investigated at room temperature. The excitation band peaks at 330 nm in a region among 250-400 nm, and the emission spectrum exhibits an intense yellowish-white broad emission centered at about 543 nm covering from 400 nm to 800 nm. The full width at half maximum (FWHM) is about 144 nm. The color coordinates of the as-synthesized YVO₄:Bi³⁺ phosphors are in a range of x = 0.358-0.374, y = 0.482-0.496. The dependence of the luminescence intensity on Bi³⁺ concentrations and heat treatment condition has also been discussed. In addition, we found that a little amount of flux NH₄Cl could enhance the Bi³⁺ luminescence intensity.     

Sol-gel preparation and characterization of uniform core-shell structured LaInO3:Sm/Tb@SiO2 phosphors

The core-shell structured LaInO₃:Ln³⁺@SiO₂ (Ln³⁺ = Sm³⁺, Tb³⁺) phosphors were realized by coating LaInO₃:Ln³⁺ phosphors on the surface of silica microspheres via a modified Pechini sol-gel process. The phase, structure, morphology, and fluorescent properties of the materials were well characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FT-IR), photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, and the kinetic decays, respectively. The results reveal that the obtained core-shell structured phosphors consist of amorphous silica core and crystalline LaInO₃:Ln³⁺ shell, which keep the uniform spherical morphology of pure silica spheres with narrow size distribution. Upon excitation by ultraviolet (UV) irradiation or electron beam, the phosphors show the characteristic emission lines of Sm³⁺ (⁴G_5/2-⁶H_5/2,7/2,9/2, orange) in LaInO₃:Sm³⁺@SiO₂ and characteristic emissions of Tb³⁺ (⁵D₄-⁷F_6,5,4,3, green) in LaInO₃:Tb³⁺@SiO₂, respectively. This kind of phosphors may have potential applications in field emission displays (FEDs) based on their uniform shape, low-cost synthetic route, and diverse luminescent properties.     

LaPO4:Eu, LaPO4:Ce, and LaPO4:Ce,Tb nanocrystals: Oleic acid assisted solvothermal synthesis, characterization, and luminescent properties

LaPO₄:Ln³⁺ (Ln = Eu, Ce, Tb) nanocrystals were successfully synthesized via a facile solvothermal process in the presence of oleic acid. The as-prepared crystals were well characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), optical spectra as well as the kinetic decay times, respectively. In the synthesis process, oleic acid as a surfactant has played a crucial role in confining the growth and size of the LaPO₄:Ln³⁺ phosphors. All the samples are well crystallized and assigned to the monoclinic monazite-type structure of the LaPO₄ phase. The prepared LaPO₄:Ln³⁺ phosphors present a narrow distribution with an average particle size of about 15 nm. Upon excitation by ultraviolet radiation, the LaPO₄:Eu³⁺ phosphors show the characteristic ⁵D₀-⁷F_1-3 emission lines of Eu³⁺, while the LaPO₄:Ce³⁺,Tb³⁺ exhibits the characteristic ⁵D₀-⁷F_3-6 emission lines of Tb³⁺. It is believed that these rare earth ion doped (Eu³⁺ ion or Ce³⁺ and Tb³⁺ ions co-doped) monoclinic monazite-type LaPO₄ nanocrystals could find potential application as future advanced optical materials.     

Vacuum ultraviolet spectroscopic properties of KSrPO4:Tb

KSrPO₄:Tb³⁺ phosphors were prepared by a solid-state method and their photoluminescence properties were investigated under vacuum ultraviolet excitation. In the excitation spectrum monitoring at 544 nm, the band in the region of 120-162 nm can be attributed to be the overlap of host absorption and charge transfer transition of O²⁻ → Tb³⁺, and the band ranging from 162 to 300 nm was assigned to the f-d transition of Tb³⁺. The photoluminescence spectrum shows that the phosphors exhibited a strong green emission around 544 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺ under the excitation of 147 nm. Optimal emission intensity was obtained when x = 7% in KSr_1-xPO₄:xTb³⁺ and the luminescent chromaticity coordinates were calculated to be (x = 0.317, y = 0.522) for KSr_0.93PO₄:7%Tb³⁺.     

Enhanced photoluminescence of GdPO4:Tb under VUV excitation by controlling ZnO content and annealing temperature

High-quality Zn-free and added GdPO₄:Tb³ green phosphors, i.e., fine size as well as smooth and spherical morphologies, were synthesized by ultrasonic spray pyrolysis. The influence of Zn²⁺ content and annealing temperature on the photoluminescence properties of the GdPO₄:Tb³ phosphors annealed at 800-1100 °C was investigated. The addition of Zn²⁺ for Gd³⁺ was highly effective for improving the photoluminescence properties of GdPO₄:Tb³. The Zn added GdPO₄:Tb³ phosphors with Zn/Gd = 0.045/0.805 showed the strongest emission of the prepared phosphors. The emission intensity at 544 nm for the GdPO₄:Tb³ phosphors with Zn/Gd = 0.045/0.805 annealed at 900 °C was 496% stronger than that at 800 °C.     

Optical and structural properties of nanostructured CeO2:Tb film

Nanostructured CeO₂:Tb³⁺ film has been fabricated on glass substrate through sol-gel technique via dip-coating process. (NH₄)₂Ce(NO₃)₆, Tb(NO₃)₃·6H₂O, ethylene glycol have been used as precursors for sol preparation. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV/VIS and photoluminescence (PL) spectral studies have been employed to analyze the structural and optical properties of the film. XRD pattern has been used to analyze the crystallite nature and calculated particle size by Scherrer equation of nanostructured CeO₂:Tb³⁺ film, found in the range 3-4 nm. SEM image has been observed to analyze the surface topography of the film which is well porous, highly agglomerated and uniformly distributed nanoparticles on the film surface. Optical band gap of nanostructured CeO₂:Tb³⁺ film has been estimated as 3.57 eV. A significant enhancement in band shape of CeO₂:Tb³⁺ spectrum has been observed in PL spectra, showed their promising usages as optical materials in optoelectronic devices.     

Blue and green emissions with high color purity from nanocrystalline Ca2Gd8Si6O26:Ln (Ln = Tm or Er) phosphors

Blue and green light emissive nanocrystalline Ca₂Gd₈Si₆O₂₆ (CGS):Tm³⁺ and CGS:Er³⁺ phosphors with high color purity were prepared by solvothermal reaction method. The structural and morphological properties of these phosphors were evaluated by the powder X-ray diffraction (XRD) and scanning electron microscopy, respectively. From the XRD results, Tm³⁺:CGS and Er³⁺:CGS phosphors had the characteristic peaks of oxyapatite in the hexagonal lattice structure. The visible luminescence properties of phosphors were obtained by ultraviolet (UV) or near-UV light and low voltage electron beam (0.5-5 kV) excitation. The photoluminescence and cathodoluminescence properties were investigated by changing the variation of Tm³⁺ or Er³⁺ concentrations and the acceleration voltage, respectively. The CGS:Tm³⁺ phosphors exhibited the blue emission due to ¹D₂→³F₄ transition, while the CGS:Er³⁺ phosphors showed the green emission due to ⁴S_3/2→⁴I_15/2 transition. The color purity and chromaticity coordinates of the fabricated phosphors are comparable to or better than those of standard phosphors for lighting or imaging devices.     

Effect of surfactants on morphology and luminescent properties of CaMoO4: Eu red phosphors

Using polyethylene glycol (PEG), Tween-80, sodium dodecyl sulphonate (SAS) and cetyltrimethylammonium bromide (CTAB) as surfactants, CaMoO₄: Eu³⁺ red phosphors were prepared by co-precipitation method and their morphology, structure and luminescent properties were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and fluorescence spectrometer. The results showed that the introduction of surfactants did not change the crystal structure of CaMoO₄: Eu³⁺ phosphors, but greatly influenced their morphology. CaMoO₄: Eu³⁺ red phosphors were prepared with 5 wt% PEG20000 having small-sized and regularly spherical morphology, and there were greater improvement in the luminescent intensity than phosphors prepared with other surfactants.     

Reddish orange long afterglow phosphor Ca2SnO4:Smprepared by sol-gel method

A reddish orange light emissive long afterglow phosphor, Ca₂SnO₄:Sm³⁺ was prepared by sol-gel method at lower temperature. The synthesized phosphors were characterized by X-ray diffraction, scanning electron micrograph images, photoluminescence spectra, afterglow decay curves and thermoluminescence spectra. Three emission peaks locate at 565 nm, 609 nm and 655 nm corresponding to CIE chromaticity coordinates of x = 0.53 and y = 0.47, which indicates the reddish orange light emitting. The fluorescent intensity and the afterglow characteristic depends on the concentration of Sm³⁺ and the optimized concentration is 1.5 mol%. The afterglow decay curves are well fitted with triple-exponential decay models. The thermoluminescence glow curves show that the Sm³⁺ induces suitable trap depth and result in the long afterglow phenomenon, and the corresponding increase or decrease in afterglow is associated with trap concentration, nearly no change in trap depth. The 1.5 mol% Sm³⁺-doped Ca₂SnO₄ sample has the biggest trap concentration and exhibit the best afterglow characteristic, its’ afterglow time is about 1 h. The phosphorescence mechanism of this long afterglow phosphor was discussed.     

Concentration-dependent luminescence and energy transfer of flower-like Y2(MoO4)3:Dy phosphor

Flower-like Y₂(MoO₄)₃:Dy³⁺ phosphors have been synthesized via a co-precipitation approach with the aid of β-cyclodextrin. The crystal structure and morphology of the phosphors were characterized by XRD (X-ray diffraction) and FE-SEM (field emission scanning electron microscopy), respectively. The excitation and emission properties of the phosphors were examined by fluorescence spectroscopy. The dependence of color coordinates on the Dy³⁺ doping concentration was analyzed. The energy transfer mechanism between Dy³⁺ ions was studied based on the Huang's theory, I-H and Van Uitert's models. It was concluded simultaneously from these three routes that the electric dipole-dipole interaction between Dy³⁺ ions is the main physical mechanism for the energy transfers between Dy³⁺.     

Photoluminescence and thermoluminescence studies of Mg2SiO4:Eu nano phosphor

Nanoparticles of Eu³⁺ doped Mg₂SiO₄ are prepared using low temperature solution combustion technique with metal nitrate as precursor and urea as fuel. The synthesized samples are calcined at 800 °C for 3 h. The Powder X-ray diffraction (PXRD) patterns of the sample reveled orthorhombic structure with α-phase. The crystallite size using Scherer's formula is found to be in the range 50-60 nm. The effect of Eu³⁺ on the luminescence characteristics of Mg₂SiO₄ is studied and the results are presented here. These phosphors exhibit bright red color upon excitation by 256 nm light and showed the characteristic emission of the Eu³⁺ ions. The electronic transition corresponding to ⁵D₀ → ⁷F₂ of Eu³⁺ ions (612 nm) is stronger than the magnetic dipole transition corresponding to ⁵D₀ → ⁷F₁ of Eu³⁺ ions (590 nm). Thermoluminescence (TL) characteristics of γ-rayed Mg₂SiO₄:Eu³⁺ phosphors are studied. Two prominent and well-resolved TL glows with peaks at 202 °C and 345 °C besides a shoulder with peak at ∼240 °C are observed. The trapping parameters-activation energy (E), order of kinetics (b) and frequency factor (s) are calculated using glow curve shape method and the results obtained are discussed.     

Photoluminescent properties of LiSrxBa1−xPO4:RE (RE = Sm, Eu) f-f transition phosphors

Rare-earth ions (Sm³⁺ or Eu³⁺) doped LiSr_xBa_1−xPO₄ (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) f-f transition phosphor powders were prepared by a high temperature solid-state reaction. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the phase structure of the sample changes from LiBaPO₄ to LiSrPO₄ when x changes from 0 to 1.0. The excitation spectra indicate that only direct excitation of rare earth ions (Sm³⁺ or Eu³⁺) can be observed. The doped rare earth ions show their characteristic emission in LiSr_xBa_1−xPO₄, i.e., Eu³⁺⁵D₀-⁷F_J (J = 0, 1, 2, 3, 4), Sm³⁺⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, 11/2), respectively. The dependence of the emission intensities of the LiSr_xBa_1−xPO₄:Sm³⁺ and LiSr_xBa_1−xPO₄:Eu³⁺ phosphors on the x value and Ln³⁺ (Ln³⁺ = Sm³⁺, Eu³⁺) concentration is also investigated.     

Preparation and characteristics of Fe3O4@YVO4:Eu bifunctional magnetic-luminescent nanocomposites

A facile direct precipitation method has been developed for the synthesis of bifunctional magnetic-luminescent nanocomposites with Fe₃O₄ nanoparticles as the core and YVO₄:Eu³⁺ as the shell. Transmission electron microscopy (TEM) images revealed that the obtained bifunctional nanocomposites had a core-shell structure and a spherical morphology. The average size was ∼150 nm, and the thickness of the shell was ∼15 nm. The X-ray diffraction (XRD) patterns showed that a cubic spinel structure of Fe₃O₄ core and a tetragonal phase of YVO₄ shell were obtained. Fourier transform infrared (FT-IR) spectra confirmed that the YVO₄:Eu³⁺ had been successfully deposited on the surface of Fe₃O₄ nanoparticles. Photoluminescence (PL) spectra indicated that the nanocomposites displayed a strong red characteristic emission of Eu³⁺. Magnetic measurements showed that the obtained bifunctional nanocomposites exhibited superparamagnetic behavior at room temperature. Therefore, the bifunctional nanocomposites are expected to develop many potential applications in biomedical fields.     

Preparation and luminescent characteristics of Sr3RE2(BO3)4:Dy (RE = Y, La, Gd) phosphors for white LED

Dysprosium-activated Sr₃RE₂(BO₃)₄ (RE = Y, La, Gd) phosphors were synthesized by a high temperature solid-state reaction method. The phase uniformity of the phosphors was characterized by X-ray powder diffraction (XRD) and the luminescence characteristics were investigated. The excitation spectra at 575 nm emission show strong spectral bands in the region of 300-500 nm. The emission spectra of the phosphors with 365 nm excitation show three bands centered at 484 nm, 575 nm and 680 nm, which originate from the transitions of ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. The effect of Dy³⁺ concentration on the emission intensity of the phosphors was investigated. The fluorescence decay curves for ⁴F_9/2 → ⁶H_13/2 excited at 365 nm and monitored at λ_em of 575 nm were measured. The decay times decreased slowly with increasing Dy³⁺ doping concentration due to a trap capturing to resonance fluorescence transfer of the activated ions and due to the exchange interactions between activated ion pairs. In order to determine the type of interaction between activated ions, the concentration dependence curves (lg(I/x) versus lg x) of Sr₃RE₂(BO₃)₄:Dy³⁺ (RE = Y, La, Gd) were plotted. The concentration quenching mechanism of the ⁴F_9/2 → ⁶H_13/2 (575 nm) transition of Dy³⁺ is the d-d interaction. All results indicate these phosphors are promising white-color luminescent materials.     

Photoluminescence and energy transfer of Ce and Tb doped oxyfluoride aluminosilicate glasses

The transmission and photoluminescence (PL) properties of Ce³⁺ or Tb³⁺ doped and Tb³⁺/Ce³⁺ codoped oxyfluoride aluminosilicate glasses were reported. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were applied to confirm the structure and thermal stability of samples. PL spectra revealed a bright and broad violet-blue emission derived from Ce³⁺ [5d (²D) → ²F_5/2,7/2] and an intense sharp green emission (543 nm) derived from Tb³⁺ (⁵D₄ → ⁷F₅) in the Ce³⁺ and Tb³⁺ doped glasses, respectively. Concentration quenching is not observed even the mole ratio of Tb³⁺ is up to 8% in Tb³⁺ doped glass. This indicates that the as-made host glass provides a good distribution of Tb³⁺ activators in glass matrix. For Tb³⁺/Ce³⁺ codoped glasses, a strong green emission corresponding to Tb³⁺ (⁵D₄ → ⁷F₅) and an energy transfer phenomenon from Ce³⁺ to Tb³⁺ were observed upon excitation with an UV wavelength (289 nm). It was also observed that their PL intensity depends on the concentration of Ce³⁺ when the concentration of Tb³⁺ is fixed. The mechanism involved in the energy transfer between Ce³⁺ and Tb³⁺ was explained with an energy level diagram.     

Preparation and luminescent properties of Eu doped Sr3La(PO4)3 phosphor

Eu²⁺-doped Sr₃La(PO₄)₃ phosphors were synthesized by solid-state reaction method. Their luminescent properties were investigated. The phosphor could be excited by ultraviolet light effectively. The emission spectra exhibit two emission peaks located at 418 nm and 500 nm, respectively. These two peaks originated from two different luminescent centers, respectively. One is nine-coordinated Eu(I) center, other is six-coordinated Eu(II) center. It was found that the doping concentration of Eu²⁺ ions affected the shape of emission spectra. As the doping concentration increasing, Eu²⁺ ions are more likely to form Eu(I) luminescent centers and emit purple light.     

Synthesis of lanthanum carbonate nanoparticles via sonochemical method for preparation of lanthanum hydroxide and lanthanum oxide nanoparticles

Lanthanum carbonate nanoparticles were synthesized from the reaction of lanthanum acetate and Na₂CO₃ under sonication via sonochemical method. Lanthanum hydroxide nanoparticles were prepared by facial hydrothermal processing from the resulted product at 110 °C for 24 h. The role of surfactant, calcination temperature and sonication time were investigated on the morphology and particle size of the products. Products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS), and Fourier transform infrared (FT-IR) spectra. La₂O₃ nanoparticles were obtained by calcinations of the nanoparticles of lanthanum carbonate at 600 °C.     

Combustion synthesis of CaSc2O4:Ce nano-phosphors in a closed system

The CaSc₂O₄:Ce³⁺ nano-phosphors were successfully prepared by a single-step combustion method at an ignition temperature as low as 200 °C in a closed autoclave using glycine as a fuel and PEG4000 as a dispersant. The samples were characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results revealed that CaSc₂O₄:Ce³⁺ nano-phosphors can be conveniently prepared at an ignition temperature as low as 200 °C, which was much lower than that in the ordinary combustion methods. The optimized ignition temperature was 220 °C. The CaSc₂O₄:Ce³⁺ nano-phosphors give a uniform particle size in the range of 15-20 nm. The low ignition temperature and the addition of PEG4000 dispersant play important roles in the formation of small sized nanoparticles. The as-prepared nano-phosphors were incompact aggregates, but highly dispersed nano-phosphors can be obtained after further ultrasonic treatment. The CaSc₂O₄:Ce³⁺ nano-phosphors give satisfactory luminescence characteristic benefiting from the closed circumstance, in which cerium atoms can be isolated from the oxidizing atmosphere and non-fluorescent Ce⁴⁺ ions can be ruled out. The present highly dispersed CaSc₂O₄:Ce³⁺ nano-phosphors with efficient fluorescence are promising in the field of biological labeling, and the present low temperature combustion method is facile and convenient and can be applied as a universal process for preparing non-aggregate oxide nano-phosphors, especially those being sensitive to air at high temperature.     

Luminescence properties of Eu and Eu doped calcium-deficient hydroxyapatite prepared in air

Eu-doped calcium-deficient hydroxyapatite Ca_8.95Eu_0.05HPO₄(PO₄)₅OH (designated CDHA:Eu) was prepared via the coprecipitation method and calcined in air. Phase purity, crystal structure and morphology of the CDHA:Eu were characterized using X-ray diffraction spectrometer and scanning electron microscopy. The photoluminescence excitation and emission spectra of Eu²⁺ and Eu³⁺ ions were measured using luminescence spectrometer. The emission spectra showed a broad emission band centered at 450 nm corresponded to the typical 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions, and sharp peaks corresponded to the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ ions. This research was focused on the site-distribution of Eu³⁺ ions. The Eu³⁺ in different sites had different spectroscopic features and the charge compensation mechanisms were also discussed.