Jiashi Sun

Optical transition, electron-phonon coupling and fluorescent quenching of La2(MoO4)3:Eu3+ phosphor

La2(MoO4)3 phosphors with various Eu3+ concentrations were prepared via a facile co-precipitation process. The crystal structure and morphology of the phosphors were characterized by means of XRD and field emission scanning electron microscope. The crystal unit cell parameters a, b, and c for the monoclinic phase La2(MoO4)3 were calculated to be 16.989, 11.927, and 16.086 A, respectively. The average size of the phosphor particles was estimated to be around 88.5 nm. The Huang–Rhys factor was derived from the phonon sideband spectra to be 0.073. The self-generated quenching process of Eu3+ was explained based on Auzel’s model, and the intrinsic radiative transition lifetime for 5D0 level was confirmed to be 0.99 ms. A new approach for calculating the Judd–Ofelt parameters was developed, meanwhile the Judd–Ofelt parameters Ωλ (λ = 2, 4, 6) of Eu3+ in La2(MoO4)3 phosphors were confirmed to be 10.70 × 10−20, 1.07 × 10−20, and 0.56 × 10−20 cm2, respectively. Finally, the optimal doping concentration for achiev...

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.

Controllable synthesis and luminescent properties of three-dimensional nanostructured CaWO4:Tb3+ microspheres.

Three-dimensional (3D) nanostructured CaWO(4):Tb(3+)microspheres assembled by submicrospindles were synthesized via a mild sonochemical route from an aqueous solution of CaCl(2), TbCl(3) and Na(2)WO(4) with the aid of surfactant Polyglycol 600 (PEG-600). The crystal structure and morphology of the as-prepared products were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Rietveld refinement was carried out on the XRD data. The results showed that the CaWO(4):Tb(3+)nanoparticles can be formed without ultrasonic irradiation or addition of PEG-600. With continuously increasing irradiation time the submicrospindles and microspheres could be self-assembled. The central diameter and length of the submicrospindles are around 190 and 500 nm, respectively. The 3D CaWO(4):Tb(3+)nanostructured microspheres with diameter of 2-4 μm were assembled by the submicrospindles. A possible formation mechanism for the 3D-structured CaWO(4):Tb(3+)microspheres was proposed. The Photoluminescent (PL) properties of Tb(3+) ions in the nanostructured CaWO(4) microspheres were studied. The energy transfer processes in CaWO(4):Tb(3+)microspheres were analyzed. The electric dipole-dipole energy transfers related to (5)D(3) level were studied by inspecting the fluorescence decay of (5)D(3) level. The energy transfer critical distance was estimated.

Size-dependent excitation spectra and energy transfer in Tb3+-doped Y2O3 nanocrystalline

Nanocrystal Y2O3 powders with different grain sizes and various doping concentrations of Tb3+ were prepared by an autocombustion reaction. The size and surface effects on the 4f-5d transitions and energy transfers between Tb3+ ions were studied by using x-ray diffraction, transmission electron microscopy, fluorescent spectra, and luminescent decay. It was found that the excitation spectra are composed of two parts: one is the contribution from the Tb3+ at/near the nanoparticle surfaces; another is from the Tb3+ inside the nanoparticles. The study on the concentration quenching and luminescent decay indicated that the energy transfers depopulating the D53 and D54 level were assigned to the mechanisms of electric dipole-dipole and exchange interaction, respectively. The size confinement greatly affects the energy transfer quenching the emission from the D53 level, but slightly affects the energy transfer quenching the emission from the D54 level.

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.

2.7 μm emission of Nd3+, Er3+ codoped tellurite glass

In this paper, we report on the observation of enhanced 2.7 mum midinfrared emission under 800 nm excitation in a Nd{sup 3+}/Er{sup 3+} codoped tellurite glass. It is also found that the green upconversion emissions from Er{sup 3+} are effectively restricted, meanwhile the {sup 4}I{sub 13/2} level of Er{sup 3+} is depopulated in the Nd{sup 3+}/Er{sup 3+} codoped tellurite glass. These results suggest that the midinfrared emission can be achieved in the oxyfluoride glasses and that codoping with Nd{sup 3+} can greatly improve the midinfrared emission performance.In this paper, we report on the observation of enhanced 2.7 μm midinfrared emission under 800 nm excitation in a Nd3+/Er3+ codoped tellurite glass. It is also found that the green upconversion emissions from Er3+ are effectively restricted, meanwhile the I413/2 level of Er3+ is depopulated in the Nd3+/Er3+ codoped tellurite glass. These results suggest that the midinfrared emission can be achieved in the oxyfluoride glasses and that codoping with Nd3+ can greatly improve the midinfrared emission performance.

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.

Fluorescence quenching of 5DJ (J = 1, 2 and 3) levels and Judd–Ofelt analysis of Eu3+ in NaGdTiO4 phosphors

NaGdTiO4 phosphors with various Eu3+ concentrations were synthesized by a solid-state reaction. The crystal structure and fluorescence properties were characterized by means of x-ray diffraction and fluorospectroscopy, respectively. An effective energy transfer from the titanate matrix to the activator Eu3+ was observed. An intense red emission originating from 5D0 ? 7F2 of Eu3+ was observed while excited at the charge transfer bands or f?f absorption bands of Eu3+. The fluorescence quenching of 5DJ (J = 1, 2 and 3) levels were studied based on the Van Uitert model. Electric dipole?dipole interaction was confirmed to be the main mechanism of the fluorescence quenching of 5DJ levels, which is responsible for the cross-relaxation between Eu3+ ions. The full optical transition intensity parameters ?? (? = 2, 4, 6) of Eu3+ in the NaGdTiO4 phosphors were calculated in the framework of Judd?Ofelt theory to be 6.024 ? 10?20, 1.512 ? 10?20 and 0.374 ? 10?20?cm2.