Xin-Yuan Sun

Enhanced emissions in self-crystallized oxyfluoride scintillating glass ceramics containing KTb 2 F 7 nanocrystals

Self-crystallized KTb2F7 oxy-fluoride glass ceramics (GC) were successfully manufactured via the traditional melt-quenching method. KTb2F7 nanocrystals were already formed after melt-quenching, which is beneficial to the realization of controllable glass crystallization to some degree for affording desirable nano-crystal size and activator partition. Their microstructural and optical properties were systemically investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), absorption spectra, photoluminescence (PL), luminescence lifetime measurements and X-ray excited luminescence (XEL). Both PL and XEL of GC samples are highly enhanced because more nanocrystals formed and grew up after heat-treatment. Our investigation suggests that transparent KTb2F7 glass ceramics may present potential application in X-ray scintillator for X-ray imaging. And our strategy that takes active ions as host may contribute to designing other oxy-fluoride GC by using active ions as host.

Near-infrared emission Ba3(PO4)2:Mn5+ phosphor and potential application in vivo fluorescence imaging.

Fluorescence imaging in the second near-infrared window (NIR-II, 1000-1350 nm) is attracting attention due to negligible tissue scattering and lower tissue autofluorescence, etc. Here, Ba3(PO4)2:Mn(5+) phosphor is prepared via solid state reaction method in air, and NIR emission band peaking at ∼1191 nm in the NIR-II region is observed. According to experiment results, Ba3(PO4)2:Mn(5+) phosphor has a great potential for the study of the NIR-II fluorescence imaging in vivo.

Role of minor quantity of Si 3 N 4 addition on the optical properties of Ce 3+ -activated borogermanate scintillating glass

Transparent and colorless CeO2-activated borogermanate glasses with about 5.60 g/cm3 were successfully synthesized by a melt-quenching method in air atmosphere. Both the optical transmittance and X-ray absorption near edge spectroscopy (XANES) spectra confirm that Ce4+ can be effectively reduced to its trivalent state, i.e. Ce3+ ions, by minor quantity of Si3N4 addition as a strong reducing agent. The luminescence characteristics excited by both ultraviolet and X-ray light were studied and the optimal content of Si3N4 was determined. The developed dense Ce3+-activated borogermanate glasses is featured with a broad emission band centered at 430 nm and a decay time of about 30 ns, which will be a promising candidate to scintillating crystals and ceramics.

Enhanced Ce3+ emission in B2O3-GeO2-Gd2O3 scintillating glasses induced by melting temperature

Transparent and colorless Ce3+-activated borogermanate glasses, with the nominal molar composition of 25B2O3-40GeO2-34Gd2O3-1CeO2-0.31Si3N4, were synthesized by melt-quenching method at different melting temperature in 1350-1450 °C region. Both the optical transmittance and X-ray absorption near edge spectroscopy (XANES) results confirm that Ce4+ can be effectively reduced to Ce3+ ions assisted with 0.31 mol% Si3N4 in air. The luminescence behaviour of Ce3+-activated borogermanate glasses excited by ultraviolet and X-ray light and to be dependent on the melting temperature, i.e. the luminescence intensity of Ce3+ ions in borogermante glass increases remarkably with an increasing in melting temperature. The possible enhanced mechanism is discussed by glass density and energy-dispersive spectroscopy (EDS) results.

Effects of substitution of BaF2 for GdF3 on optical properties of dense oxyfluoride borogermanate scintillating glasses

Abstract Eu 3+ -activated B 2 O 3 -GeO 2 -37Gd 2 O 3 -3Eu 2 O 3 -(15– x )GdF 3 - x BaF 2 (0≤x≤15) scintillating glasses with the density of 6.1–6.3 g/cm 3 were synthesized by a melt-quenching method. The substitution of BaF 2 for expensive GdF 3 in oxyfluoride borogermanate glasses slightly decreased the glass density within 3.0%. Their optical properties were characterized by transmittance, photoluminescence (excitation and emission), and X-ray excited luminescence (XEL) spectra in detail. The emission intensity of Eu 3+ ions increased with the elevated x values. The Eu–O covalancey nature and the local environment of Eu 3+ ions were evaluated by Judd-Ofelt results. It was found that the covalency property of Eu–O bond increased with increasing x values.

Luminescence behavior of Li2Sr1-3x/2EuxSiO4 red phosphors for LED applications

Red-emitting Li(2)Sr(1-3x/2)Eux SiO4 0 ≤ x ≤ 0.5) phosphors were synthesized at 900 °C in air by a solid-state reaction. The synthesized phosphors were characterized by X-ray powder diffraction, photoluminescence (PL) excitation (PLE) and PL spectra. The results from the PLE spectra suggest that the strong 394 nm excitation peak associated with the (5) L6 state of Eu(3+) ions is of significance for near ultraviolet pumped white light-emitting diodes and solid-state lighting. It is also noted that the position of the charge transfer state of Eu(3+) ions shifts towards the higher energy side (blue shift) by increasing the content of Eu(3+) ions. The predominant emissions of Eu(3+) ions under 394 nm excitation are observed at 580, 593, 614, 656 and 708 nm, which are attributed to the (5) D0 → (7)FJ (J = 0, 1, 2, 3 and 4), respectively. The PL results reveal that the optimal content of the red-emitting Li2 Sr(1-3x/2)Eux SiO4 phosphors is x = 0.475. Simulation of the white light excited by 394 nm near ultraviolet light has also been carried out for its potential white light-emitting diode applications.

Highly efficient Na_5Gd_9F_32:Tb^3+ glass ceramic as nanocomposite scintillator for X-ray imaging

Mono-crystal scintillator materials suffer from issues of complex, time-consuming techniques as well as small volume. Here, bulk Tb3+-doped Na5Gd9F32 glass ceramic (GC) scintillators with relatively high transparency were successfully manufactured via the melt-quenching method with further thermal treatment. Their structural and luminescent properties were systemically investigated by a series of characterization techniques including XRD, TEM, absorption spectra, photoluminescence (PL) excitation and emission spectra, lifetime measurements, and X-ray excited luminescence (XEL). Luminescent spectroscopy results show that the optimum doping concentrations of Tb3+ in precursor glass (PG) and GC systems are both 4 mol%. The XEL intensity of PG is about 64% of that of a commercial Bi4Ge3O14 (BGO) scintillator with the same thickness. Benefiting from the incorporation of Tb3+ ions into Na5Gd9F32 nanocrystals, enhanced PL and XEL of Tb3+ ion are realized after crystallization. The internal PL quantum yield of GC is 43.0% and the XEL intensity of GC reaches 130% of that of a BGO scintillator. Our results demonstrate that Na5Gd9F32 GC may act as an efficient scintillator with large-volume and low-cost.

Spectroscopic and energy transfer properties of Dy3+-doped, Tb3+/Dy3+-codoped dense oxyfluoride borogermanate scintillating glasses

Dy3+-, Tb3+-activated, and Tb3+/Dy3+-coactivated oxyfluoride borogermanate scintillating glasses with the density of about 6.50 g/cm3 were successfully synthesized by a melt-quenching method. The structure and optical properties including transmittance, photoluminescence (excitation and emission spectra), photoluminescence decay, and X-ray excited luminescence (XEL) behaviors were studied in detail. Our results reveal that the energy transfer efficiency from Dy3+ to Tb3+ ions increases with an increase of Tb3+ concentration. The energy transfer mechanism is determined to be electric dipole–dipole interaction. However, the XEL intensity of Tb3+ decreases with the incorporation of sensitizer Dy3+ into borogermanate scintillating glass, which may result from the different mechanisms under ultraviolet light and X-ray excitation.

Luminescent Properties of

Borogermanate scintillating glasses with nominal composition of (70-x)B2O3-xGeO2-29Gd2O3-1Eu2O3 (20 ≤ x ≤ 45) were synthesized by melt-quenching method. Their structure and optical properties were characterized by transmittance spectra, Fourier transform infrared spectra (FTIR), Raman spectra, excitation and emission spectra, and X-ray excited luminescence (XEL) spectra in detail. Transparency of the as-synthesized borogermanate glasses exceeds 80% in 400-800 nm regions. The cut-off edges of borogermanate glasses are in the vicinity of 308 nm, and they shift towards longer wavelength (red-shifted) with the elevated x values. Both glass density and mean molecular weight increase in a linear relationship with increasing x values. With increasing x values, the characteristic emission intensity of both Gd3+ and Eu3+ ions decrease progressively under 276 nm excitation, while these emission intensities seem irregular under 394 nm excitation. The strongest X-ray excited luminescence (XEL) intensity occurs at x = 35 glass sample, which is improved about 35% with comparison to the x = 20 one. Additionally, the information on glass structure is also discussed by FTIR and Raman spectra.

{\rm Eu}^{3+}

We report a study on the heat transport of an S = 1 Haldane chain compound Ni(C3H10N2)2NO2ClO4 at low temperatures and in magnetic fields. The zero-field thermal conductivities show a remarkable anisotropy for the heat current along the spin-chain direction (κb) and the vertical direction (κc), implying a magnetic contribution to the heat transport along the spin-chain direction. The magnetic-field-induced change of the spin spectrum has obviously opposite impacts on κb and κc. In particular, κb(H) and κc(H) curves show peak-like increases and dip-like decreases, respectively, at ∼9 T, which is the critical field that minimizes the spin gap. These results indicate a large magnetic thermal transport in this material.