Bining Tian

Self-assembled 3D flower-shaped NaY(WO4)2:Eu3+ microarchitectures: Microwave-assisted hydrothermal synthesis, growth mechanism and luminescent properties

Three dimensional (3D) flower-shaped microarchitectures of NaY(WO4)2 were synthesized via a microwave-assisted hydrothermal process in the presence of trisodium citrate (Na3Cit) and a post-calcination process. The effects of reaction conditions on the morphology of precursor microstructures were studied. It was found that Na3Cit, as the chelating agent and shape modifier, plays a key role in the microstructure growth. A possible growth mechanism for the flower-shaped microarchitectures was proposed. The as-formed precursor can completely transform into NaY(WO4)2 with its original flower-shaped morphology via a heat treatment process. The concentration and temperature quenching behaviors of Eu3+ fluorescence in the flower-shaped NaY(WO4)2 were studied, and the optimal doping concentration was confirmed, meanwhile the activation energy was obtained. Judd-Ofelt parameters Ωλ (λ = 2, 4 and 6) of Eu3+ in the flower-shaped NaY(WO4)2 phosphor were obtained by using the emission spectrum of Eu3+, moreover the radiative transition properties were analyzed.

Excitation pathway and temperature dependent luminescence in color tunable Ba5Gd8Zn4O21:Eu3+ phosphors

A series of polycrystalline Ba5Gd8Zn4O21:Eu3+ phosphors were synthesized by a solid state reaction for the first time. The crystal structures were examined by means of X-ray diffraction. The luminescence spectra and decay curves were investigated as a function of Eu3+ concentration and temperature. It was found that the luminescent color of phosphor can be adjusted from white to red with the increase of Eu3+ concentration. Interestingly, emission spectra with different 5D0/5D1,2,3 ratios were observed when excited at 276 (corresponding to the O2− → Eu3+ charge transfer band) and 395 nm (f–f transition 7F0 → 5L6). The energy transfers between Eu3+ ions in Ba5Gd8Zn4O21 have been confirmed to be resonant type via exchange interaction for the 5D0 level and electric dipole–dipole interaction for 5DJ (J = 1–3) levels. Temperature dependent measurements revealed that the crossover process is the main mechanism for quenching luminescence of the 5D0 level of Eu3+ in the Ba5Gd8Zn4O21:Eu3+ phosphors. Finally, Judd–Ofelt parameters of Eu3+ in the Ba5Gd8Zn4O21 phosphors were calculated by a facile method in the framework of the J–O theory, in which the refractive index of Ba5Gd8Zn4O21 was deduced to be about 1.95.

Size-dependent upconversion luminescence and temperature sensing behavior of spherical Gd2O3:Yb3+/Er3+ phosphor

Yb3+/Er3+ codoped spherical Gd2O3 phosphors with different particle sizes were prepared via a urea-assisted homogeneous precipitation process by adjusting the molar ratio of rare earth ions and urea followed by annealing at high temperature. The phases, morphologies, and luminescence properties of the as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and upconversion luminescence (UCL) spectra, respectively. The spherical Gd2O3:Yb3+/Er3+ phosphors showed size-dependent upconversion luminescence properties under the excitation of 980 nm-laser. The temperature sensing behavior of spherical Gd2O3:Yb3+/Er3+ phosphors with different particle sizes was studied based on the change of emission intensities from two thermally coupled 2H11/2 and 4S3/2 levels. It is interesting to observe that the sensing sensitivity of the sample increases with decreasing particle size and a sensitivity of 84 × 10−4 K−1 was obtained for the sample with a particle size of 45 nm. Finally, Judd–Ofelt theory was used for explaining and predicting the effect of particle size on sensing sensitivity.

Microwave-assisted hydrothermal synthesis and temperature sensing application of Er3+/Yb3+ doped NaY(WO4)2 microstructures

Laurustinus shaped NaY(WO4)2 micro-particles assembled by nanosheets were synthesized via a microwave-assisted hydrothermal (MH) route. The growing mechanisms for the obtained resultants with various morphologies were proposed based on the observation of scanning electron microscopic (SEM) images. It was found that Na3Cit added into the reaction solution greatly influenced the formation and size dimension of the nano-sheets, furthermore determined assembling of the laurustinus shaped micro-particles. The temperature sensing performance of NaY(WO4)2:Er(3+)/Yb(3+) was evaluated. Thermal effect induced by the 980nm laser irradiation in laurustinus-shaped NaY(WO4)2:Er(3+)/Yb(3+) phosphor was studied. It was found that the green upconversion luminescence intensity increased in the first stage of laser irradiation, and then decreased after reaching a maximum. Based on the thermal sensing technology the laurustinus NaY(WO4)2:Er(3+)/Yb(3+) microparticles were used as thermal probe to discover thermal effect of upconversion luminescence in laurustinus NaY(WO4)2:Tm(3+)/Yb(3+) micro-particles.

Excellent optical thermometry based on single-color fluorescence in spherical NaEuF 4 phosphor

Temperature-dependent luminescence of spherical NaEuF₄ phosphors with different particle sizes was studied. The thermally coupled ⁵D₀ and ⁵D₁ level of Eu³⁺ was observed. The linear dependence of emission intensities of ⁵D₀ level of NaEuF₄ phosphor on temperature confirmed the excellent temperature sensing performance. Sensitivity up to 0.43% is achieved via decreasing the particle size, which is higher than that of reported thermometry based on upconversion of lanthanide ions. Moreover, the original luminescent intensity of 90% was recovered after 10 temperature-changed cycles, indicating good sensing stability. Therefore, spherical NaEuF₄ phosphor might be a promising candidate for optical temperature sensors.

Temperature sensing and optical heating in Er3+ single-doped and Er3+/Yb3+ codoped NaY(WO4)2 particles

Temperature sensing properties and laser induced thermal effects in rare earth doped materials could inspire some critical applications in accurate temperature detection and thermal therapy. In this paper, a microwave-assisted hydrothermal method was used to synthesize rare earth doped NaY(WO4)2 microstructures. Microstructured NaY(WO4)2 samples with various morphologies were derived by controlling the amount of trisodium citrate in reaction solution. Microscopic image and crystal structure of the obtained samples were characterized by XRD, SEM and HRTEM. It was found that all the received samples exhibited pure phase, and the Cit3−/Y3+ ratio considerably influenced the morphology but the rare earth concentration did not. The temperature sensing performance for the samples with various morphologies and different rare earth concentrations was evaluated. It was confirmed that both the morphology and doping concentration slightly affected the temperature property. Furthermore, based on the temperature sensing technique of Er3+ doped materials, the 980 nm laser irradiation induced thermal effect in NaY(WO4)2 microstructures was studied. It was also found that the sample temperature was very sensitive to the sample morphology and the doping concentration of Er3+ and Yb3+.

Hydrothermal synthesis and tunable luminescence of persimmon-like sodium lanthanum tungstate:Tb3+, Eu3+ hierarchical microarchitectures

Persimmon-like NaLa(WO(4))(2) microarchitectures were prepared via hydrothermal process with using trisodium citrate (Na(3)Cit) as chelated reagent and characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), photoluminescence (PL), and fluorescent dynamics. The influences of Na(3)Cit concentration, organic additivities, and reaction time on the morphologies of NaLa(WO(4))(2) phosphor were studied. The results revealed that Na(3)Cit species had double functions of strong ligand and structure-directing reagent that could efficiently control the formation of persimmon-like NaLa(WO(4))(2) microarchitectures. The possible mechanism for the growth of persimmon-like NaLa(WO(4))(2) microarchitectures was attributed to the Ostwald ripening mechanism. The energy transfer from Tb(3+) to Eu(3+) in the persimmon-like NaLa(WO(4))(2) phosphors was observed. The energy transfer efficiencies and emission colors can be tuned by changing the concentration of Eu(3+). Finally, it was deduced that the electric dipole-dipole interaction (D-D) is the main mechanism for energy transfer between Tb(3+) and Eu(3+) in the persimmon-like NaLa(WO(4))(2) phosphor.

Improved upconversion luminescence and temperature sensing in Mo6+-doped LuNbO4:Er3+ phosphor under 1550 nm excitation

LuNbO4: Mo6+,Er3+ phosphors were prepared via a solid-state reaction and characterized by x-ray diffraction (XRD) and upconversion luminescence (UCL) as well as temperature-dependent UC spectra. Under 1550 nm excitation, the characteristic UCL of the Er3+ ion, which originates from a three-photon process, is observed. An obvious UC enhancement can be found when the Mo6+ ions are doped, which may be attributed to the lower symmetry around Er3+. The optical thermometry behavior was studied as well. It is found that the maximum sensitivity is improved from 0.0053 K−1 to 0.0069 K−1 and the temperature revolution increases from 1.0 K to 0.7 K. Therefore, this work will provide a path for improving UCL and sensing sensitivity in Er3+-doped systems at an excitation of 1550 nm.