Synthesis,structural, photoluminescence and mechanoluminescence properties of Tb<Superscript>3+</Superscript>: Ca<Subscript>2</Subscript>Gd<Subscript>2</Subscript>W<Subscript>3</Subscript>O<Subscript>14</Subscript> novel green nanophosphors

Novel green nanophosphors Ca₂Gd₂W₃O₁₄: Tb³⁺ were synthesized by solid state reaction method. From the X-ray diffraction profiles it is observed that Tb³⁺: Ca₂Gd₂W₃O₁₄ phosphors were crystallized in the form of tetragonal structure. The scanning electron microscopy (SEM) image shows that the particle size is at around 300 nm. In addition to these the prepared powder phosphors were also examined by the energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and mechanoluminescence (ML) spectra. Emission spectra of Tb³⁺: Ca₂Gd₂W₃O₁₄ nanophosphors have shown bright green emission at 545 nm (⁵D₄ → ⁷F₅) with an excitation wavelength λ_exci = 374 nm (⁷F₆ → ⁵G₆). ML spectra shows the radiation effect on the Ca₂Gd₂W₃O₁₄: Tb³⁺ nanophosphors and from that it was observed that these phosphors are very less sensitive for lower exposure.     

Luminescence studies on Eu<Superscript>2+</Superscript> and Tb<Superscript>3+</Superscript> doped Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript> phosphors

Eu²⁺ and Tb³⁺ doped Ca₂MgSi₂O₇ phosphors were synthesized by conventional solid-state reaction. The phase formation was confirmed by X-ray powder diffraction technique and refined lattice parameters were calculated by rietveld refinement process using Celref v3. The photoluminescence (PL) excitation and emission spectra were investigated. The phosphors exhibited broaden green emitting luminescence peaking at 520 nm when excited at 374 nm source. Morphological studies were carried out using Scanning electron microscopy (SEM) images of the sample with optimum PL emission. The dependence of photoluminescence intensity on co-dopant concentration and the kinetic parameters were also reported. Time resolved fluorescence spectroscopy (TRFS) is used to investigate the decay in luminescence signals with respect to time. The sample proved to be a good long lasting material, which makes it useful in emergency signs, textile printing, textile exit sign boards and electronic instrument dial pads etc.     

Synthesis,photoluminescence and mechanoluminescence properties of Eu<Superscript>3+</Superscript> ions activated Ca<Subscript>2</Subscript>Gd<Subscript>2</Subscript>W<Subscript>3</Subscript>O<Subscript>14</Subscript> phosphors

A new series of Eu³⁺ ions-activated calcium gadolinium tungstate [Ca₂Gd₂W₃O₁₄] phosphors were synthesized by conventional solid-state reaction method. The X-ray diffraction patterns of the powder samples indicate that the Eu³⁺: Ca₂Gd₂W₃O₁₄ phosphors are of tetragonal structure. The prepared phosphors were well characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), and mechanoluminescence (ML) spectra. PL spectra of Eu³⁺: Ca₂Gd₂W₃O₁₄ powder phosphors have shown strong red emission at 615 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ _exci = 392 nm (⁷F₀ → ⁵L₆). The energy transfer from tungstate groups to europium ions has also reported. Mechanoluminescence studies of Eu³⁺: Ca₂Gd₂W₃O₁₄ phosphors have also been explained systematically.     

Hydrothermal synthesis of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> nanorods and its growth mechanism and luminescence properties

Homogeneous Y₂O₃:Eu³⁺ nanorods with the lengths of several micrometres were successfully synthesised on a large scale by using a urea-assisted hydrothermal method and a post-calcining process. In this study, the influences of urea content and NaOH concentration on the oriented growth, photoluminescence (PL) and electroluminescence (EL) intensity enhancement of Y₂O₃:Eu³⁺ were investigated. As a precipitant for isotropic growth, urea can counteract the effect of NaOH on oriented growth along the c-axis during hydrothermal treatment. The Y₂O₃:Eu³⁺ powders exhibited a strong red emission centred at 613 nm under either 245 nm UV excitation or the direct current high electric field. The PL intensity of the Y₂O₃:Eu³⁺ phosphor prepared with 0.3 g of urea reached 141 % that of the sample prepared under the same conditions but without urea. The strategy for controlling the oriented growth, PL and EL enhancement of Y₂O₃:Eu³⁺ can be extended to the synthesis of other inorganic nano/micromaterials.     

Morphology and luminescent properties of Al<Superscript>3+</Superscript>/Mg<Superscript>2+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Al³⁺/Mg²⁺ doped Y₂O₃:Eu phosphor was synthesized by the glycine-nitrate solution combustion method. In contrast to Y₂O₃:Eu which showed an irregular shape of agglomerated particles (the mean particle size >10 μm), the morphology of Al³⁺/Mg²⁺ doped Y₂O₃:Eu crystals was quite regular. Al³⁺/Mg²⁺ substituting Y³⁺ in Y₂O₃:Eu resulted in an obvious decrease of the particle size. Meanwhile, higher the Al³⁺/Mg²⁺ concentration, smaller the particle size. In particular, the introduction of Al³⁺ ion into Y₂O₃ lattice induced a remarkable increase of PL and CL intensity. While, for Mg²⁺ doped Y₂O₃:Eu samples, their PL and CL intensities decreased. The reason that causes the variation of PL and CL properties for Al³⁺ and Mg²⁺ doped Y₂O₃:Eu crystals was concluded to be related to sites of Al³⁺ and Mg²⁺ ions inclined to take and the difference of ion charge.     

Ultraviolet upconversion luminescence in Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Yb<Superscript>3+</Superscript>,Tm<Superscript>3+</Superscript> nanocrystals and its application in photocatalysis

Infrared-to-ultraviolet upconversion luminescence agent Y₂O₃:Yb³⁺,Tm³⁺ was prepared by a combustion method using citrate as a fuel/reductant. The prepared sample was characterized by X-ray diffraction, SEM, and fluorescence spectrophotometer. Two unusual ¹I₆ → ³H₆ (~297 nm) and ¹D₂ → ³H₆ (~363 nm) emissions from Tm³⁺ ions were observed at room temperature under 980-nm laser excitation. The change of upconversion emission intensity depending on the Yb³⁺ concentrations was discussed. The results showed that modest Yb³⁺ doping could make the upconversion emission of Tm³⁺ intense, and high Yb³⁺ concentrations might lead to fluorescence quenching. Moreover, the influence of ultraviolet upconversion luminescence on the photodegradation of methyl orange aqueous solution under solar light irradiation in the presence of TiO₂ catalyst doped with Y₂O₃:Yb³⁺,Tm³⁺ was also investigated. It was concluded from the experiment of this study that TiO₂/Y₂O₃:Yb³⁺,Tm³⁺ composite had higher photocatalytic activity than pure TiO₂ under solar light. This study would make TiO₂ utilize sunlight more efficiently and accelerate the practical application of photocatalytic technology in water treatment region.     

Combusion synthesis,structural and photo-physical characteristics of Eu<Superscript>2+</Superscript> and Dy<Superscript>3+</Superscript> co-doped SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> phosphor nanopowders

In this research, we reported the synthesis of Eu²⁺ and Dy³⁺ co-doped SrAl₂O₄ phosphor nanopowders with high brightness and long afterglow by urea-nitrate solution combustion synthesis (SCS) at 600 °C, followed by heating the resultant combustion ash at 1,200 °C in a weak reductive atmosphere (5% H₂ + 95% N₂). The broad-band UV-excited luminescence of the SrAl₂O₄: Eu²⁺, Dy³⁺ nanopowders was observed at λ _max = 517 nm due to transitions from the 4f⁶5d¹ to the 4f⁷ configuration of the emission center (Eu²⁺ ions). The excitation spectra consist of 240- and 254 nm broad peaks. Finally, it was found that the optimum ratio of urea is 2.5 times higher than theoretical quantities for the best emission condition of SrAl₂O₄: Eu²⁺, Dy³⁺ phosphor nanopowders.     

Synthesis and luminescence properties of a novel Eu<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript> co-doped Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript> whiskers by a gel nano-coating method

Al₁₈B₄O₃₃:Eu³⁺, Tb³⁺ whiskers have been successfully prepared by a simple gel nano-coating method using aluminum isopropoxide as the starting materials. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL), and thermogravimetric analysis (TGA) were used characterize the samples. The results show coexistence of the crystal phase Al₁₈B₄O₃₃, amorphous phase, and Eu³⁺, Tb³⁺ ions of the samples with initial addition Al/B ratios from 3 to 1 are incorporated into the amorphous phase. The Al₁₈B₄O₃₃:Eu³⁺, Tb³⁺ whiskers are very straight with an average diameter of 600 nm and lengths ranging from 5 to 10 μm. Under ultraviolet excitation at 365 nm, samples show mainly exhibit the characteristic emission of Eu³⁺ corresponding to \( ^{ 5} {\text{D}}_{ 0} \to {\text{F}}_{ 1 , 2} \) transitions due to an efficient energy transfer occurs from Tb³⁺ to Eu³⁺.     

Influence of Mg<Superscript>2+</Superscript>/Ga<Superscript>3+</Superscript> doping on luminescence of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> phosphors

Mg²⁺/Ga³⁺ doped Y₃Al₅O₁₂:Ce³⁺ phosphors were synthesized through a solid state reaction. The phase and luminescent of the synthesized phosphors were investigated. For Ga³⁺ codoped Y_2.96Ce_0.04Al_(5?x)Ga_xO₁₂ phosphors, the emission intensity increases with the increase of Ga³⁺ concentration up to Y_2.96Ce_0.04Al_4.80Ga_0.20O₁₂ and then decreases with a further increase of Ga³⁺ concentration, but the emission peak shifts to shorter wavelength continuously in the Ga³⁺ doping concentration range of 0.05–0.25. For Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors, the emission intensity decreases and the emission peak shifts to longer wavelength continuously in the Mg²⁺ doping concentration range of 0.02–0.12. The emission spectra of Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors demonstrate that the codoped Mg²⁺/Ga³⁺ ions not only induce the enhancement of Y_2.96Ce_0.04Al₅O₁₂ emission intensity but also lead to the red shift of Y_2.96Ce_0.04Al₅O₁₂ emission peak. The decay lifetimes decrease in Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al₅O₁₂ phosphors due to defects formed by substitutions of Y³⁺ by Mg²⁺/Ga³⁺.     

Synthesis and photoluminescence properties of Eu<Superscript>3+</Superscript>-activated SrZnO<Subscript>2</Subscript>

Synthesis, X-ray diffraction, and photoluminescence (PL) investigations of SrZnO₂ doped with Eu³⁺ were carried out in order to characterize the material. The emission spectra showed a broad band emission at 525 nm attributed to oxygen defect centers in the host matrix, along with peaks corresponding to the ⁵D₀ → ⁷F _j (j = 1, 2) transitions of Eu ion under 250 nm excitation. PL decay time studies were done to confirm these investigations. Time-resolved emission spectrometric (TRES) study was carried out to extract the emission spectra of the Eu ion which was buried under the broad band emission. After giving suitable delay times and by choosing a proper time gate, transitions due to ⁵D₀ → ⁷F _j (j = 0, 1, 2, 3, and 4) could be observed. Judd–Ofelt intensity parameters and other radiative properties for the system were evaluated from this emission spectrum and decay time data by adopting standard procedure. The color coordinates of the system were also evaluated and plotted on a standard CIE index diagram. The observations showed that the SrZnO₂:Eu³⁺material has near white light emission (also considering the emission from host) whereas, the extracted emission spectrum due to only Eu ions has a near red emission.     

Green photoluminescence and afterglow of Tb-doped SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>

Trivalent terbium-doped strontium aluminate (SrAl₂O₄:Tb³⁺) nanoparticles were synthesized via the sol–gel combustion technique, and the green photoluminescence (PL) and afterglow were evaluated to clarify the afterglow mechanism of SrAl₂O₄:Tb³⁺. The green PL of SrAl₂O₄:Tb³⁺ with characteristic emissions at 488, 543, 586, and 622 nm indicated that Tb dopant acts as the luminescent center of the PL. Contrarily, the green afterglow of SrAl₂O₄:Tb³⁺ was a broadband spectrum with its peak centered at around 520 nm, but no traces of Eu were found in SrAl₂O₄:Tb³⁺ phosphors within the detection limit of 1 μg/g. The band structures and density of states of SrAl₂O₄:Tb³⁺ were calculated within the framework of density functional theory. Both the ground state of Tb³⁺ dopant and the trap levels of oxygen vacancy were quantitatively determined in the band gap of SrAl₂O₄. Our results suggest that the deep electron trap of oxygen vacancy in the host acts as the luminescent center of the green afterglow from SrAl₂O₄:Tb³⁺. A possible afterglow mechanism is proposed to shed fresh light on the green afterglow of SrAl₂O₄:Tb³⁺.     

A novel green emitting phosphor Ca1.5Y1.5Al3.5Si1.5O12:Tb

Vacuum ultraviolet (VUV) excitation and emission properties of Tb³⁺ ion doped silico-aluminate phosphor Ca_1.5Y_1.5Al_3.5Si_1.5O₁₂:Tb³⁺ was studied. Upon excitation with vacuum ultraviolet (VUV) and near UV light excitation, the phosphor showed strong green-emission peaked at 545 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺, and the highest PL intensity at 545 nm was found at a content of about 14 mol% Tb³⁺. The 4f–5d transition absorption of Tb³⁺ is in the range from 150 nm to 260 nm, and there is an energy transfer from the host to the rare earth ions. Field emission scanning electron microscopy (FE-SEM) images showed the particle size of the phosphor was less than 3 μm.     

Hydrothermal synthesis and luminescence properties of core-shell-structured PS@SrCO<Subscript>3</Subscript>:Tb<Superscript>3+</Superscript> spherical particles

Nanocrystalline SrCO₃:Tb³⁺ phosphor layers were coated on monodisperse and spherical polystyrene particles by a typical hydrothermal synthesis without further annealing treatment, resulting in the formation of core-shell-structured polystyrene@SrCO₃:Tb³⁺ particles. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, as well as lifetimes were employed to characterize the resulting composite particles. Under ultraviolet excitation, the polystyrene@SrCO₃:Tb³⁺ phosphors show the characteristic ⁵D₄–⁷F _J (J = 6, 5, 4, 3) emission lines with green emission ⁵D₄–⁷F₅ (544 nm) as the most prominent group. The obtained core-shell phosphors are potentially applied in fluorescent lamps.     

Study of the effect of Li<Superscript>+</Superscript> concentration on the photoluminescence properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphors

Y₂O₃:Eu³⁺ phosphors were prepared by hydrothermal method. Effect of the doping concentration of Eu³⁺ on the photoluminescence properties of Y₂O₃:Eu³⁺ phosphor was studied in details. It was found that the strongest emission intensity is achieved as atomic ratio of Y³⁺ to Eu³⁺ is 8. As concentration of Eu³⁺ exceeds the critical concentration, the emission intensity decreases dramatically due to the concentration quenching of Eu³⁺. Also, the effect of Li⁺ on the photoluminescence performance of the Y₂O₃:Eu³⁺ phosphor is studied in this work. According to the results, the doping of Li⁺ may greatly improve the PL performance of the Y₂O₃:Eu³⁺ phosphors due to the flux effect and improved crystallinity caused by the doping of Li⁺.     

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.%.     

Spindlelike Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> nanorod bundles: hydrothermal synthesis and photoluminescence properties

Uniform spindlelike Y(OH)₃ nanorod bundles were successfully prepared for the first time via a simple hydrothermal method at 200 °C for 12 h with the presence of Na₂H₂EDTA · 2H₂O (EDTA). Scanning electron microscope (SEM) images show that the obtained Y(OH)₃ spindlelike nanorod bundles have a length of about 11 μm and a diameter of about 2 μm in the middle part. The nanorod bundles are composed of numerous nanorods, and all these nanorods are orientationally aligned and grow uniformly along the bundles. The individual nanorod is with typical width of about 100 nm, thickness of about 40 nm, and length longer than 1 μm. The effects of reaction temperature, reaction time, and the concentration of NaOH and EDTA on the sizes and morphologies of the products have been investigated. The possible formation mechanism of the nanorod bundles was suggested. Spindlelike Y₂O₃ nanorod bundles were obtained after thermal treatment of the as-obtained Y(OH)₃ nanorod bundles at 700 °C for 4 h. X-ray powder diffraction (XRD) results demonstrate that the as-prepared Y(OH)₃ and Y₂O₃ are attributed to hexagonal phase and cubic phase, respectively. Eu³⁺ doped Y₂O₃ nanorod bundles were also prepared and their photoluminescence (PL) properties were investigated.     

Synthesis and photoluminescence properties of LiEu(W,Mo)<Subscript>2</Subscript>O<Subscript>8</Subscript>:Bi<Superscript>3+</Superscript> red-emitting phosphor for white-LEDs

LiEu_1−x (W_2−y Mo _y )O₈:xBi³⁺ series red-emitting phosphors were synthesized by solid state reaction. The structure, morphology, and photoluminescent properties of phosphors were studied by X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectrum, respectively. X-ray powder diffraction analysis showed that the as-obtained phosphors belong to the scheelite structure. The average particle size of the investigated phosphor was about 8 μm. The excitation spectrum exhibits a charge-transfer broad band along with some sharp peaks from the typical 4f–4f transitions of Eu³⁺. Under excitation of UV, near-UV, or blue light, these phosphors showed strong red emission at 615 nm due to ⁵D₀–⁷F₂ transition of Eu³⁺. The incorporation of Mo⁶⁺ into LiEuW₂O₈:Bi³⁺ could induce red-shift of the charge-transfer broad band and a remarkable increase of photoluminescence. The highest red-emission intensity was observed with LiEu_0.80Mo₂O₈:0.20Bi³⁺. Compared with the commercial red-emitting phosphor, Y₂O₂S:Eu³⁺, the emission intensity of LiEu_0.80Mo₂O₈:0.20Bi³⁺ phosphor is much stronger than that of Y₂O₂S:Eu³⁺ and its chromaticity coordinates are closer to the standard values than that of the commercial phosphor. The optical properties of LiEu_0.80Mo₂O₈:0.20Bi³⁺ phosphor make it attractive for the application in white-light-emitting diodes (LEDs), in particular for near-UV InGaN-based white-LEDs.     

Solid state synthesis,microstructure and photoluminescence of Eu<Superscript>3+</Superscript> and Tb<Superscript>3+</Superscript> activated strontium tungstate

The Eu³⁺ and Tb³⁺ ions activated SrWO₄ phosphors have been synthesized by solid state method. The crystal structures and morphologies of the products are characterized by Powders X-ray Diffraction (XRD) and scanning electronic microscopy (SEM). The results indicated that both SrWO₄:Eu³⁺ and SrWO₄:Tb³⁺ phosphors belong to tetragonal phase, and the particles of the phosphors become aggregate with the increase of calcinations temperature. Analyzed by luminescent spectra, the dominant emission of Eu³⁺ in SrWO_4, which is the typical hypersensitive transition ⁵D₀ → ⁷F₂ (613 nm), and the green emission (⁵D₄ → ⁷F₅) intensity of Tb³⁺ in SrWO₄:Tb³⁺ is also dominant. The reaction temperature had obvious influence on the luminescent properties. The intensity reached the strongest when it is sintered at 900 °C. Therefore, we can try to select the right temperature in order to obtain the ideal product.     

Synthesis and luminescent characterization of YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>:Tb<Superscript>3+</Superscript> phosphors

YAl₃(BO₃)₄:Tb³⁺ phosphors were fabricated by the sol–gel method. The phosphor showed prominent luminescence in green due to the magnetic dipole transition of ⁵D₄–⁷F₅. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 nm under UV excitation. It is shown that the 11% of doping concentration of Tb³⁺ ions in YAl₃(BO₃)₄:Tb³⁺ phosphors is optimum.     

Temperature effect on the photoluminescence intensity and Eu<Superscript>2+</Superscript> excited state lifetime in EuGa<Subscript>2</Subscript>S<Subscript>4</Subscript> and EuGa<Subscript>2</Subscript>S<Subscript>4</Subscript>:Er<Superscript>3+</Superscript>

The photoluminescence (PL) spectra and Eu²⁺ excited state lifetime of EuGa₂S₄ and EuGa₂S₄:Er³⁺ have been studied in the range 78–500 K. The spectra show a band at 545 nm, due to the 4f ⁶5d → 4f ⁷(⁸ S _7/2) transition. With increasing temperature, the full width at half maximum Γ(T) of the PL band of EuGa₂S₄ and EuGa₂S₄:Er³⁺ crystals increases from 0.15 to 0.22 and from 0.13 to 0.19 eV, respectively. Over the entire temperature range studied, Γ(T) is a linear function of T ^1/2. The 545-nm emission intensity and Eu²⁺ excited state lifetime in EuGa₂S₄ and EuGa₂S₄:Er³⁺ vary exponentially with temperature. The luminescence quenching energies evaluated from the Arrhenius plots of I(10³/T) and τ(10³/T) coincide (0.10 eV) within the error of determination.