Doped NaGd Research Articles

Luminescence and temperature sensing properties of Eu3+-Tb3+ doped NaGd(MoO4)2 glass ceramics

A series of NaGd(MoO4)2 glass ceramics containing Eu3+-Tb3+ were fabricated using the melt-curing crystallization method. These glass ceramics were subjected to various analyses, such as differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and light transmittance curve analysis, to determine the optimal heat treatment conditions, which were determined to be 680 ℃/1.5 h. The XRD Rietveld analysis results confirmed the successful incorporation of Eu3+ and Tb3+ ions into the NaGd(MoO4)2 lattice structure. Moreover, the glass ceramics exhibited a smaller optical bandgap than the precursor glass, as observed by absorption spectroscopy. The energy transfer from Tb3+ to Eu3+ was demonstrated through the excitation spectra, emission spectra, and fluorescence decay curves. The primary mechanism responsible for this energy transfer was identified as a dipoledipole interaction. The ability to produce multicolor tunable emission was achieved by varying the Eu3+ doping concentration at a fixed Tb3+ concentration. The fluorescence intensity ratio and temperature dependence of Tb3+ and Eu3+ were used to calculate the relative sensitivity (Sr), which reached a maximum of 3.34 % K−1 at 458 K. In conclusion, Eu3+-Tb3+ co-doped glass ceramics have promising potential for application in the fields of light-emitting diodes and temperature sensing.

Enhancing luminescence, tuning emission colors, and improving temperature sensitivity in NaGd(MoO4)2 multilayer thin films

A thin film with a sandwich structure of NaGd(MoO4)2: Yb3+@Yb3+/Ho3+@Yb3+ was successfully prepared using the spin-coating method. A comparative analysis of this sandwich-structured film with other films having the same doping composition and spin coating times showed that the emission intensity of the former was enhanced. We attribute the luminescence enhancement of the sandwich-structured film to the presence of Yb3+ ions in both the top and bottom layers. This overcomes the concentration quenching effect imposed by the Yb3+/Ho3+ system's concentration limit. Moreover, the warm white light emission of the NaGd(MoO4)2:Yb3+@Yb3+/Tm3+@Yb3+/Ho3+@Yb3+ film was successfully achieved by introducing Yb3+/Tm3+ layers, and tuning from blue to white to yellow was realized by adjusting the number of spin coatings and the proportion of Yb3+/Tm3+ and Yb3+/Ho3+ layers. Finally, we found that sandwich-structured films have better temperature sensitivity compared to powder materials and other structured films. These results indicate that rare-earth doped NaGd(MoO4)2 thin films have great potential in the fields of luminescence, color display, and temperature sensing. The adjustment of luminescence color can be achieved by manipulating the micro/nano film structure, and the spin-coating process can effectively improve the temperature sensing characteristics.

Tb3+ and/or Sm3+ doped NaGd(MoO4)2 nanocrystalline transparent glass-ceramics: Preparation, tunable luminescence, and energy transfer

Tb3+ and/or Sm3+ doped SiO2–B2O3–Na2O–ZnO–MoO3-Gd2O3 transparent glass-ceramics containing NaGd(MoO4)2 nanocrystals were successfully prepared by the melt-quenching method and subsequent heat treatment process. The optimal schedule to achieve heat treatment was crystallized at 650 °C for 5 h. The strongest green luminescence (545 nm: 5D4→7F5) was obtained under 376 nm excitation when the Tb2O3-doped amount was 0.3 mol%. A thorough investigation was conducted to explore the mechanism of energy transfer from Tb3+ ions to Sm3+ ions, which is caused by quadrupole-quadrupole interactions. Tb3+-Sm3+ co-doped SiO2–B2O3–Na2O–ZnO–MoO3-Gd2O3 glass-ceramics can achieve green, yellow, and red multi-color tunable luminescence as the amount of Sm2O3 doping changes, which indicates that it holds promising potential in applications such as ultraviolet-transformed white light-emitting diodes and various optical apparatus.

Luminescence and temperature-dependent sensitivity of Yb3+/Er3+ doped glass ceramics containing NaGd(MoO4)2 nanocrystals

Yb3+/Er3+ doped NaGd(MoO4)2 glass ceramics (GCs) were manufactured by melting quenching and subsequent controllable crystallization method, and the structure, transmissivity, up-conversion luminescence and temperature sensitive characteristics were studied. The results show that NaGd(MoO4)2 nanocrystals are embedded in the precursor glass (PG). The crystallization temperature and soaking time directly affect the crystallinity of the glass. Enhanced up-conversion luminescence in the GC sample is clearly observed. According to thermal coupling emission states, the maximum relative sensitivity (Sr-max) of 1.32 % K−1 and absolute sensitivity (Sa-max) of 1.90 % K−1 between 297 K and 437 K are acquired in the GC700-2h sample. This finding reveals that the obtained GC materials have great potential in optical temperature measurement.

Tunable emission and applications of Ln3+ doped NaGd(WO4)2 nanocrystals via a facile solvothermal process

Abstract Double tungstate crystal has outstanding capabilities of gain media for the application in mode-locked ultrafast lasers. Among them, NaGd(WO4)2:Ln3+ is widely using in laser, pH sensing or lighting devices. However, general synthetic methods require high temperature, long reaction time or adjustment of solution pH, which is seriously hinder their related applications. Here, we synthesized NaGd(WO4)2:Ln3+ nanocrystals through a solvothermal strategy. The synthesis was designed to avoid the solvent effect of water. Our nanoparticles with a rod shape and average size is ∼3.8 × 46.3 nm. Furthermore, Terbium and Europium ions co-doped in a single NaGd(WO4)2 host has been obtained, energy migration from Terbium ions to Europium ions also implemented. A series of emission colours (from green to white) were obtained. At last, a distinguished performance NaGd(WO4)2:0.03Tb,0.03Eu based UV-LED equipment was realized. Their adjustable emissions, convenient preparation method and special morphology reveal that NaGd(WO4)2:Ln3+ is a potential candidate for solid-state lasers and UV-LEDs applications.

Thermoplasmonic enhancement of upconversion in small-size doped NaGd(Y)F4 nanoparticles coupled to gold nanostars.

Plasmon enhancement of luminescence is a common strategy to boost the efficiency of both fluorescence and upconversion via the augmented local electromagnetic field. However, the local heating produced when exciting the plasmon resonance of metallic nanoparticles is often overlooked. As higher temperatures are usually detrimental for radiative processes, only the electromagnetic contribution is exploited for enhancement. We show here that for small size (<20 nm) rare-earth doped β-NaGd(Y)F4 upconversion nanoparticles (UCNPs), the photothermal properties of gold nanostars (AuNSs) can be used to enhance the total emission intensity. On the contrary, for UCNPs of larger size, the thermoplasmonic effect is adverse for the emissivity. Therefore, we developed a novel strategy to enhance the emission intensity by combining the thermoplasmonic effect on AuNSs with the size-dependent thermal properties of UCNPs. Furthermore, by following the integrated intensity ratio between the emission lines of Er3+, 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, a direct correlation between the local temperature and the emission intensity could be established. Optical thermometry measurements show that the thermoplasmonic effect in AuNSs, with a plasmon absorption band close to the excitation wavelength, can produce an increment of the local temperature of more than 100 °C when exposed to 976 nm continuous-wave laser light at 50 W cm-2 of power density. The results provided here are relevant for the design and implementation of plasmon-enhanced luminescent devices, upconversion solar-cells, bioprobes and also for hyperthermia.

Well-defined octahedral Sm3+, Dy3+ doped NaGd(MoO4)2 microcrystals: facile hydrothermal synthesis and luminescence properties

Well-defined NaGd(MoO4)2 octahedral microcrystals with singly-doped Sm3+ or Dy3+ ions and co-doped Sm3+/Dy3+ ions were prepared through a mild hydrothermal route without any additives. The as-synthesized products were characterized by means of powder X-ray diffraction, scanning electron microscopy and luminescence spectra. It was found that the pH value of the initial solution played a crucial role in determining the morphology, size and emission intensity of final products. The possible formation mechanism for the product with uniform octahedral morphology was investigated and discussed according to the time-dependent experiments. Furthermore, under near-UV excitation, NaGd(MoO4)2:Sm3+ and NaGd(MoO4)2:Dy3+ phosphors exhibited the characteristic emissions of Sm3+ and Dy3+, respectively. Meanwhile, Dy3+ could effectively transfer the excitation energy to Sm3+ under near-UV excitation when they were co-doped in NaGd(MoO4)2 host. Moreover, the CIE color coordinates of NaGd(MoO4)2: 0.05Dy3+, xSm3+ samples were located in white light region suggesting that the as-synthesized phosphors might be promising candidates in the fields of white light diodes, full-color displays and optoelectronic devices.

The hydrothermal synthesis and morphology-dependent optical temperature sensing properties of Er3+ doped NaGd(WO4)2 phosphor

NaGd(WO4)2: Er3+ phosphors by using sodium citrate (Na3Cit, Na3C6H5O7) as chelating agent were synthesized via hydrothermal method. The structure and morphology were characterized and analyzed by the X-ray diffraction and field emission scanning electron microscopy. It was found that Na3Cit added into the reaction solution considerably influenced the morphologies of samples. The temperature-dependent down-conversion emission spectra of NaGd(WO4)2: Er3+ phosphor under the excitation of 377.5nm fluorescence with different ratios of Cit3-/Re3+ have been measured. The temperature sensing performance for the samples 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 sensing sensitivities increased with the increase of ratios of Cit3-/Re3+, and the temperature sensing sensitivity can reach a relatively high value of 0.0128K−1, which was obtained for the sample with the ratio of Cit3-/Re3+ was 1.5. Finally, the physical mechanism of morphology-dependent temperature sensing sensitivity change was explained.

A novel anion doping strategy to enhance upconversion luminescence in NaGd(MoO4)2:Yb3+/Er3+ nanophosphors.

We propose a novel and efficient F- anion doping strategy for enhancing upconversion luminescence in upconversion nanophosphors. NaGd(MoO4)2:Yb3+/Er3+ nanophosphors doped with different F- contents are synthesized hydrothermally. Rietveld refinement results obtained from X-ray diffraction data indicate that the Gd-O bond length decreases and the O-Gd-O bond angle varies with increasing F- content, resulting in augmented local crystal field strength and distorted local site symmetry of the dopant lanthanide sites. Judd-Ofelt analysis suggests that the calculated radiative quantum efficiency of the 4S3/2 level and the radiative branching ratio of 4S3/2 → 4I15/2 transition in F--doped NaGd(MoO4)2:Yb3+/Er3+ nanophosphors are much greater than those in F- anion-free samples. It is inferred that F- anion doping helps to reduce the nonradiative transition probabilities based on the luminescence dynamics. Rietveld refinement results and Judd-Ofelt analysis confirm jointly that doping of interstitial F- anions could enhance local crystal field strength with odd parity and modify site symmetry of the lanthanide activator ions, leading to enhanced radiative transitions and inhibited nonradiative transitions. A maximum of 17-fold enhancement of total emission intensity is found in NaGd(MoO4)2:Yb3+/Er3+/F- nanophosphors compared with F- anion-free counterparts. The proposed F- anion doping strategy provides an alternative approach for enhancing upconversion luminescence efficiency and could be extended to other inorganic upconversion nanomaterials.

Luminescence characterization of sol-gel derived Pr3+ doped NaGd(WO4)2 phosphors for solid state lighting applications

In the present work, xPr3+:NaGd(WO4)2 (0.5 ≤ x ≤ 5.0 mol%) sub-micron phosphors were synthesised by sol-gel method. Low cost precursors of metal nitrates and low temperature thermal treatment was used compared to conventional solid state reaction. The formation of highly crystalline phosphors with tetragonal structure was confirmed by XRD and increase of Pr3+ ions content in host matrix leads to expansion of the unit cell volume. The surface morphology, size and particle distribution of the phosphors were observed by field emission scanning electron microscopy (FE-SEM). A rectangular shape particle with a size distribution ranging from 400 to 600 nm and tightly packed surface was seen in FE-SEM micrographs. The various internal and external phonon modes vibration corresponding to double tungstate structure was observed in Raman spectra. The optical properties of the synthesised phosphors were explored by ultraviolet visible (UV–Vis) absorption in diffuse reflectance and photoluminescence (PL) measurements. UV–Vis measurements distinguished the host and Pr3+ absorption and also reveal an increase in optical band gap values with an increase of Pr3+. The PL measurements show various emissions from green and red regions under 450 nm. The maximum intensity emission at 489 nm is due to 3P0 → 3H4 transition of Pr3+. From the maximum emission the critical doping concentration was calculated to be at 3.5 mol% and critical distance between two adjacent Pr3+ ions as 20.43 Å.

Multifunctional Eu-doped NaGd(MoO4)2 nanoparticles functionalized with poly(l-lysine) for optical and MRI imaging.

A method for the synthesis of non-aggregated and highly uniform Eu3+ doped NaGd(MoO4)2 nanoparticles is reported for the first time. The obtained particles present tetragonal structure, ellipsoidal shape and their size can be varied by adjusting the experimental synthesis parameters. These nanoparticles, which were coated with citrate anions and functionalised with PLL, have also been developed in order to improve their colloidal stability in physiological medium (2-(N-morpholino)ethanesulfonic acid, MES). A study of the luminescent dynamics of the samples as a function of the Eu doping level has been conducted in order to find the optimum nanophosphors, whose magnetic relaxivity and cell viability have also been evaluated for the first time for this system, in order to assess their suitability as multifunctional probes for optical (in vitro) and magnetic bioimaging applications.

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.

Solid state reaction synthesis and photoluminescence properties of Dy3+ doped NaGd(MoO4)2 phosphor

Dy3+ doped NaGd(MoO4)2 phosphors were synthesized by a traditional solid-state reaction route using NH4HF2 as a flux. The influence of calcination temperature on the crystal structure and spectral properties was studied, and the optimum calcination temperature for producing Dy3+ doped NaGd(MoO4)2 phosphor was experimentally confirmed. The concentration quenching of Dy3+ fluorescence and excitation-wavelength dependent spectroscopic properties were studied. On the base of both the Van Uitert's and I-H models, the electric dipole–dipole (D–D) interaction was ascribed to be the main physical mechanism responsible for energy transfer between Dy3+ ions. It was also discovered that the color coordinates of the Dy3+ doped NaGd(MoO4)2 phosphor depends on the Dy3+ doping concentration and the excitation wavelength.

Epitaxial Growth of NaGd0.935Yb0.065(WO4)2 Layers on Lattice Matched Tetragonal Double Tungstate Substrates for Ultrafast Thin Disk Lasers

Liquid-phase epitaxial growth of Yb 3+ doped NaGd(WO 4 ) 2 crystalline layers has been obtained on Y modified NaGd(WO 4 ) 2 Czochralski grown single crystal substrates. It is shown that the lattice parameter of the layer and substrate can be equalized by proper selection of the Yb and Y compositions. The epitaxial layers obtained are highly transparent, with thicknesses in the range 10―70 μm, and with crystallographic quality close to that of the used substrates. The spectroscopic properties of Yb 3+ in the layer are anisotropic and similar to those of Yb-doped NaGd(WO 4 ) 2 single crystals. The layers are envisaged as optical gain media for the design of ultrafast modelocked thin disk lasers.

Energy migration in the Ce3+-doped Na–Gd phosphate glasses

Luminescence decay kinetics of Ce3+-doped Gd3+-sensitized Na-phosphate glasses was measured within 4–300K and analyzed to reveal the mechanism of energy migration through the Gd3+ subsystem to the Ce3+ emission centers. Dependencies of the asymptotic decay rates on the temperature are used to identify the type of phonon assistance in the Gd3+–Gd3+ energy transfer.