Co-doped NaGd Research Articles

Upconversion Luminescence Properties of Ho3+/Tm3+/Yb3+ Co-doped NaGd(MO4)2 Prepared by Hydrothermal Method

In this paper, Ho$$^{3+}$$/Tm$$^{3+}$$/Yb$$^{3+}$$-doped NaGd(MO$$_{4})_{2}$$ phosphors were prepared using the hydrothermal method and the effect of Yb$$^{3+}$$ doping amount on the luminescence properties of these phosphor materials was investigated. NaGd(MO$$_{4})_{2}$$ was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectral analysis. The results showed that Ho$$^{3+}$$/Tm$$^{3+}$$/Yb$$^{3+}$$-doped NaGd(MO$$_{4})_{2}$$ has tetragonal phase structures, and doping with rare-earth ions decreases the cell parameters of NaGd(MO$$_{4})_{2}$$. NaGd(MO$$_{4})_{2}$$:Ho$$^{3}$$/Tm$$^{3+}$$/Yb$$^{3+}$$ generates blue, green, and red lights at 477, 545, and 659 nm, respectively, under an excitation of 980 nm. The emission of these three lights is called a three-photon process. As the doping ratio of Yb$$^{3+}$$ increases, the colour coordinates of samples gradually approach the white region from the red region, enabling NaGd(MO$$_{4})_{2}$$:0.1Ho/1Tm/20Yb to exhibit white emission. Doping with Yb$$^{3 + }$$ increases the energy transfer and quantum efficiencies of NaGd(MO$$_{4})_{2}$$. When the concentration of Yb$$^{3+}$$ reached 30%, the quantum efficiency of NaGd(MO$$_{4})_{2}$$ reached the maximum value of 188.37%. Overall, NaGd(MO$$_{4})_{2}$$:Ho/Tm/Yb has broad application prospects in the field of white lighting.

Influence of rare earth doping and calcination temperature on temperature sensitivity of gadolinium molybdate nanoparticle

NaGd(MoO4)2: Er3+/Yb3+ up-conversion fluorescence materials was prepared by a sol-gel method. And the effects of activator ion doping concentration, sensitizer ion doping concentration and calcination temperature on the temperature sensitivity of NaGd(MoO4)2: Er3+/Yb3+ materials were studied. The samples were characterized by XRD, SEM and fluorescence spectra. The temperature sensitivity of different powder was calculated by using the temperature measurement formula of fluorescence intensity ratio. At this time, the results show that the temperature sensitivity is the highest when the concentration of Er3+ is 0.5% in the range of 0.3–2.0% and when the concentration of Yb3+ is 28% in the range of 16–32%. Under the condition of 0.5% Er3+/ 28% Yb3+, a higher value of 0.0268 K−1 can be obtained. Then, the change of temperature sensitivity with doping concentration was analyzed based on the theory of energy transition and the analysis of fluorescence lifetime. In addition, with the calcination temperature increasing from 700 ℃ to 1100 ℃, it is found that the fluorescence intensity and temperature sensitivity of the calcination temperature at 800 ℃ are both great. At the same time, the influence of doping concentration of Er3+， doping concentration of Yb3+ and calcination temperature on the sensitivity was compared. It was found that the influence of Er3+ ion doping concentration was more significant. These results indicate that Er3+ and Yb3+ co-doped NaGd(MoO4)2 powder has a great application prospect in temperature sensing.

Frequency upconversion based thermally stable molybdate phosphors in a temperature sensing probe

Er3+–Yb3+ co-doped NaGd(MoO4)2 phosphors with different concentrations of Er3+ and Yb3+ ions have been successfully synthesized via a high-temperature solid-state reaction method.

Up/down conversion luminescence and energy transfer of Er3+/Tb3+ activated NaGd(WO4)2 green emitting phosphors

A series of double scheelite-type tungstate green phosphors NaGd(WO4)2:Er3+, Tb3+ were synthesized by a hydrothermal route and subsequent calcination process, and they were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometry (EDS), photoluminescence spectroscopy and fluorescence lifetime measurements. The phosphors take on octahedral microcrystals with a mean side length of ~2 μm. In the single doped phosphors system, the energy transfer processes from WO42− to Er3+ or Tb3+ were discussed. The quenching concentrations of Er3+ and Tb3+ are 0.05 and 0.07, respectively. The critical distances for Er3+ and Tb3+ ions are calculated to be 14.28 Å and 12.76 Å, respectively. When doping Er3+/Tb3+ is applied in the single compound, the concentration quenching effect of Tb3+ ions occurs via a resonant-type dipole-dipole interaction as well as that of Er3+ ions. Under the excitation with ultraviolet (378 nm) or infrared (980 nm) light, the Er3+/Tb3+ co-doped NaGd(WO4)2 phosphors emit strong green emission. The obtained samples with bright emission intensity and appropriate decay time are suitable for use as green phosphors in the near ultraviolet LEDs and bioimaging applications.

Influence of reaction parameters on the luminescence properties of monodisperse NaGd(1−x−y)(WO4)2:xEu3+,yTb3+ phosphor by molten salt synthesis

Eu3+ activated and Eu3+, Tb3+ co-activated monodisperse sodium double tungstates NaGd(WO4)2 phosphors were prepared by molten salt method at 750 °C for 10 h using NaCl as a flux. The crystal structure and morphology of the as-synthesized phosphors were measured by XRD and SEM, respectively. The photoluminescence properties were characterized by PL spectra, decay lifetime and CIE. The presence of NaCl plays an important role in the morphology and luminescence properties. In this work, NaCl and one of the raw material Na2CO3 in a certain proportion will form a low eutectic salt to decrease the reaction temperature and benefit the formation of monodisperse NaGd(WO4)2 crystals. The color of Eu3+ and Tb3+ co-doped NaGd(WO4)2 phosphors can be tuned from creamy white to orange, red and green by adjusting the doping concentration of rare earth ions, since the emission contain the broad blue-green emission origin from NaGd(WO4)2 host and characteristic red and green emission origin from Eu3+ and Tb3+ ions. The electroluminescent spectra and CIE measurement shows that the LED device with NaGd(1−x)(WO4)2:xEu3+ (x = 0.24) phosphor can be excited by 365 nm and 380 nm LED chip, and their CIE coordinate is (x = 0.45, y = 0.45) and (x = 0.36, y = 0.37), Ra is 80.3 and 86.3, Tc is 3196 and 4556 K, respectively. As a single-component phosphor, NaGd(WO4)2:Eu3+,Tb3+ have potential application in UV-pumped WLEDs.

Hydrothermal synthesis combined with calcination of NaGd(SO4)2 nanoparticles and their luminescent properties from single doped Eu3+ and co-doped Yb3+,Er3+

The NaGd(SO4)2: Eu3+/Yb3+,Er3+ nanoparticles were successfully synthesized by a facile hydrothermal method combined with calcination. DTA-TG-DTG, FT-IR, and XRD results reveal that the precursor is composed of gadolinium hydrate with sulfate groups and can convert into pure NaGd(SO4)2 nanoparticles with a dispersed fishing net shape after calcined at 800 °C for 2 h. Upon excitation at 273 nm UV light, the emission spectra of Eu3+-doped phosphors consist of 5D0 → 7Fj (j = 1, 2, 3, 4) transitions and the target NaGd(SO4)2: Eu3+ shows a highest red luminescent intensity than NaGd(SO4)2·H2O: Eu3+ and Gd2O3: Eu3+ phosphors, corresponding to the 5D0 → 7F2 transition of Eu3+. The calculated lifetime of NaGd(SO4)2 is determined to be 2.345 ms. The up-conversion luminescence (UCL) mechanism of Yb3+ and Er3+ co-doped NaGd(SO4)2 and Gd2O3 phosphors were also discussed in the typical energy level diagram for their possible UCL processes.

Optical temperature sensing properties of Er3+, Yb3+ co-doped NaGd(MoO4)2 phosphor

Er3+, Yb3+ co-doped NaGd(MoO4)2 phosphors by using sodium citrate as chelating agent were synthesized by hydrothermal method. The structure and morphology were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The temperature-dependent up-conversion spectra of Er3+, Yb3+ co-doped NaGd(MoO4)2 phosphor under the excitation of 980nm laser with different ratios of Cit3−/Re3+ has been measured. It was found that the Cit3−/Re3+ ratio considerably influenced the sample's morphology. The temperature sensing performance for the samples with various morphologies was studied based on the change of emission intensities from two thermally coupled 2H11/2 and 4S3/2 levels of Er3+. It was found that the temperature sensitivity can up to a relative high value of 0.0161K−1, which was obtained for the sample with the ratio of Cit3−/Re3+ was 0.5. Finally, physical mechanism of morphology-dependent temperature sensing sensitivity was explained and predicted.

Luminescent properties and energy transfer mechanism of NaGd(MoO4)2:Sm3+, Eu3+ phosphors

Sm3+ singly doped NaGd(MoO4)2 and Sm3+, Eu3+ co-doped NaGd(MoO4)2 phosphors by using sodium citrate as chelating agent were synthesized via hydrothermal method. The structure and morphology were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). During the synthesis process, the Na3Cit concentration plays a crucial role in determining the morphology and particle size of the products. The optimal doping concentration in Sm3+ singly doped NaGd(MoO4)2 phosphor was confirmed. The relevant parameters of energy transfer in the NaGd(MoO4)2: Sm3+, Eu3+ phosphors have been calculated based on the fluorescent dynamic analysis. Finally, on the analysis of luminescent spectra and fluorescent dynamics, the main energy transfer mechanism between Sm3+ and Eu3+ in NaGd(MoO4)2 phosphor is confirmed to be electric dipole-dipole interaction, and energy transfer pathway is from 4G5/2 state of Sm3+ to 5D0 state of Eu3+ rather than 5D1 of Eu3+ ions.

NaGd(MoO<sub>4</sub>)<sub>2</sub>: Tb<sup>3+</sup>, Eu<sup>3+</sup>荧光粉的水热合成及发光性质研究

采用水热法合成了NaGd(MoO4)2: Tb3+, Eu3+荧光粉。利用X射线衍射(XRD)对样品进行了测试，所制样品的衍射峰与标准卡片PDF#25-08282一致。样品的发光性质通过激发光谱和发射光谱进行了表征。证实了从Tb3+到Eu3+有能量传递的存在。 Tb3+, Eu3+ codoped NaGd(MoO4)2 phosphors were prepared by the method of hydrothermal pro- cess. The structure of the phosphors was characterized by the X-ray diffraction (XRD), which was corresponded to JCPDS card with # 25-0828. The photoluminescence properties of the prepared products were characterized by the excitation and emission spectra. The energy transfer from Tb3+ to Eu3+ in NaGd(MoO4)2 phosphors was confirmed.

Single-component and warm-white-emitting phosphor NaGd(WO4)2:Tm3+, Dy3+, Eu3+: synthesis, luminescence, energy transfer, and tunable color.

Tm(3+), Dy(3+), and Eu(3+) codoped NaGd(WO4)2 phosphors were prepared by a facile hydrothermal process; they were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectrometer (EDS), photoluminescence spectra, and fluorescence lifetime. The results show that the novel octahedral microcrystals with a mean side length of 2 μm are obtained. Under the excitation of ultraviolet, individual RE(3+) ion (Tm(3+), Dy(3+), and Eu(3+)) activated NaGd(WO4)2 phosphors exhibit excellent emission properties in their respective regions. Moreover, when codoping Dy(3+) and Eu(3+)/Tm(3+) in the single component, the energy migration from Dy(3+) to Eu(3+) has been demonstrated to be a resonant type via a dipole-quadrupole mechanism as well as that from Tm(3+) to Dy(3+) ions, of which the critical distance (R(Dy-Eu)) is calculated to be 11.08 Å. More significantly, in the Tm(3+), Dy(3+), and Eu(3+) tridoped NaGd(WO4)2 phosphors, the energy migration of Tm(3+)-Dy(3+)-Eu(3+), utilized for sensitizing Eu(3+) ions besides compensating the red component at low Eu(3+) doping concentration, has been discussed first. In addition, under 365 nm near-ultraviolet radiation (nUV), the color-tunable emissions in octahedral NaGd(WO4)2 microcrystals are realized by giving abundant blue, green, white, yellow, and red emissions, especially warm white emission, and could be favorable candidates in full-color phosphors for nUV-LEDs.

Sol–gel synthesis and photoluminescence studies on colour tuneable Dy3+/Tm3+ co-doped NaGd(WO4)2 phosphor for white light emission

A series of Dy3+/Tm3+ ion co-doped NaGd(WO4)2 (NGW) phosphors were synthesised by a sol–gel method at low temperature for white light emission. The structural and luminescence properties of the synthesised phosphors were studied by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman and photoluminescence techniques. In Dy3+/Tm3+:NGW phosphors, the dopant ions substituted Gd3+ ions that are located in S4 sites of NGW host lattice. In NGW host, under UV excitation the Dy3+ ions have shown strong yellow (4F9/2→6H13/2) and comparatively weak blue (4F9/2→6H15/2) emission transitions at 575 and488 nm, respectively. Due to deficient blue colour the overall emission falls in yellow region. Hence, Tm3+ ions having strong blue emission at 455nm corresponding to the transition 1D2 →3F4 were co-activated along with Dy3+ ions in NGW matrix. By changing the doping concentrations of Tm3+ and Dy3+ ions in NGW, white light emission was tuned by 353nm excitation wavelength. Their corresponding colour co-ordinates were calculated and found to be very close to the white colour chromaticity co-ordinates (0.333, 0.333).

Growth, thermal and spectral properties of Tm3+, Ho3+ co-doped NaGd(MoO4)2 Crystal

A Tm3+/Ho3+:NaGd(MoO4)2 crystal was grown by the Czochralski method. The XRD results matched standard data from JCPDS file, which accorded with scheelite structure with an I41/a space group. Thermal properties of crystal were analyzed by using the TG–DSC curve. The melting point and specific heat are 1182°C and 0.5J/gK at 300K, respectively. The Spectral properties of the Tm3+/Ho3+:NaGd(MoO4)2 crystal were investigated, including room temperature absorption spectrum and fluorescence spectrum. The absorption cross-section of Tm3+ at 796nm is 4.33×10−20cm2 with pertinent full widths at half maximum (FWHM) of 10nm. The intensity parameters, spontaneous emission probability, fluorescence branching ratios and radiative lifetimes were calculated by Judd–Ofelt theory. The emission cross-sections are 1.47×10−20cm2 and 1.36×10−20cm2 for Tm3+ at 1850nm and Ho3+ at 2000nm respectively. The lifetime of 5I7→5I8 (Ho3+) was 4.263ms.

Surfactant-assisted hydrothermal synthesis of octahedral structured NaGd(MoO4)2:Eu3+/Tb3+ and tunable photoluminescent properties

NaGd(MoO4)2:Eu3+/Tb3+ phosphors were synthesized via a facile hydrothermal method with a surfactant-assisted environment. The properties were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and photoluminescence (PL). The XRD patterns and FESEM image indicate that NaGd(MoO4)2:Eu3+/Tb3+ phosphors crystallize well with the scheelite structure and the morphology of the sample is octahedral. The octahedral morphology of the phosphors is found to be manipulated by the glutamic acid. The luminescent properties reveal that under 277nm excitation, Eu3+ and Tb3+ doped NaGd(MoO4)2 phosphors show strong red and green emission. Moreover, Eu3+ and Tb3+ co-doped NaGd(MoO4)2 phosphors display the multicolor luminescence when excited by a single excitation wavelength or different excitation wavelengths, and the luminescence colors of the samples can be tuned from red, yellow, yellow–green, to green when adjusting the doping concentration of the activator ions. Furthermore, the possible energy transfer mechanism in Tb3+ and Eu3+ co-doped NaGd(MoO4)2 was proposed in term of the experimental results and analysis. The as-prepared phosphors may find potential applications in the field such as color displays.

Near infrared to visible upconversion emission in Er3+/Yb3+ co-doped NaGd(WO4)2 nanoparticles obtained by hydrothermal method

The Er3+/Yb3+ co-doped NaGd(WO4)2 nanoparticles have been prepared by a simply hydrothermal synthesis procedure. The crystal structures and morphologies of the products were characterized by XRD, SEM and FT-IR spectroscopy. The average grain size of these samples depended on the annealing temperature, increasing with the increase of the temperature. The intense visible upconversion and near infrared luminescence of the Er3+/Yb3+ co-doped NaGd(WO4)2 nanoparticles under 975nm excitation could be observed. The luminescence intensities of the samples depended on the size of the nanoparticles and Yb3+ concentration. The transition mechanisms of the upconversion emission can be ascribed to a two-photon absorption process.

Hydrothermal synthesis and upconversion luminescence of NaGd(WO4)2 co-doped with Ho3+ and Yb3+

The Ho3+/Yb3+ co-doped NaGd(WO4)2 phosphors with different concentrations of Yb3+ were prepared by a facile hydrothermal route. X-ray diffraction and scanning electron microscopy were used to study the structure of the samples. The upconversion (UC) emission spectra of the samples were measured under 980nm excitation with different pumping power. Intense red luminescence at 625–675nm, weak blue luminescence at 458–492nm, green luminescence at 523–565nm and near infrared luminescence at 736–770nm emitted by Ho3+ were observed, and their emission intensities changed with the Yb3+ concentration. The transition mechanisms of the UC luminescence were also discussed.

Pure near-infrared to near-infrared upconversion of multifunctional Tm3+ and Yb3+ co-doped NaGd(WO4)2 nanoparticles

Pure near-infrared to near-infrared upconversion and paramagnetism were observed in NaGd(WO4)2:Tm3+,Yb3+ nanoparticles, suggesting that they are promising materials for applications in high-contrast bio-imaging and bio-separation.

Luminescence, energy-transfer and tunable color properties of single-component Tb3+ and/or Sm3+ doped NaGd(WO4)2 phosphors with UV excitation for use as WLEDs

Tb3+ and/or Sm3+ codoped NaGd(WO4)2 microcrystals were prepared and energy transfer mechanisms of WO42− → Sm3+ and Tb3+ → Sm3+ were studied. The color-tunable emissions are investigated, for nUV-LED applications.