Qiu Jianbei

Green long-after-glow luminescence of Tb3+ in Sr2SiO4

The green long-after-glow luminescence from Tb3+-doped Sr2SiO4 phosphors, which are synthesized by the high temperature solid state reaction in a reductive atmosphere, is observed in this paper. The results show that under ultraviolet excitation, the obtained phosphors produce an intense green-lighting-emission from the Tb3+, and the green-lighting long-after-glow luminescence related to Tb3+ can last half an hour after the irradiation source has been removed. Moreover, the effects of co-doping Li+, Dy3+, Er3+, Gd3+, and Yb3+ with Tb3+ on the decay properties and thermoluminescence properties are investigated to confirm the long-after-glow mechanism.

Effects of Li+ on photoluminescence of Sr3SiO5: Sm3+ red phosphor

The structure and photoluminescence (PL) properties of Sr3SiO5: Sm3+ and Li+-doped Sr3SiO5: Sm3+ red-emitting phosphors were investigated. Samples were prepared by the high-temperature solid-state method. PL spectra show that the concentration quenching occurs when the Sm3+ concentration is beyond 1.3 mol% in Sr3SiO5: Sm3+ phosphor without doping Li+ ions. The concentration-quenching mechanism can be explained by the electric dipole—dipole interaction of Sm3+ ions. The incorporation of Li+ ions into Sr3SiO5: Sm3+ phosphors, as a charge compensator, improves the PL properties. The lithium ions also suppress the concentration quenching in Sm3+ with concentration increased from 1.3 mol% to 1.7 mol%.

Preparation and characterization of nanosized GdxBi0.95?xVO4:0.05Eu3+ solid solution as red phosphor

A complete solid solutions with monophasic zircon-type structure of vanadates of formula GdxBi0.95−xVO4:0.05Eu3+ (x = 0–0.95) are synthesized by combined method of co-precipitation and hydrothermal synthesis. Their microstructures and morphologies are characterized by X-ray powder diffraction and transmission electronic microscope, and the results show that each of all the samples has a monophasic zircon-type structure. The absorption spectrum of the prepared phosphor shows a blue-shift of the fundamental absorption band edge with increasing the gadolinium content. Under UV-light and visible-light excitation, all the prepared phosphors show the typical luminescence properties of Eu3+ in the zircon-type structure. The emission intensity of GdxBi0.95−xVO4:0.05Eu3+ (x = 0.55) is strongest in all samples under UV-light and visible-light excitations. Finally, the mechanisms of luminescence of Eu3+ in the GdxBi0.95−xVO4:0.05Eu3+ (x = 0–0.95) solid solutions are analyzed and discussed.

A novel strong green phosphor: K3Gd(PO4)2:Ce3+, Tb3+ for a UV-excited white light-emitting-diode

A series of K3Gd1−x−y(PO4)2:xCe3+, yTb3+ phosphors are synthesized by the solid-sate reaction method. X-ray diffraction and photoluminescence spectra are utilized to characterize the structures and luminescence properties of the as-synthesized phosphors. Co-doping of Ce3+ enhances the emission intensity of Tb3+ greatly through an efficient energy transfer process from Ce3+ to Tb3+. The energy transfer is confirmed by photoluminescence spectra and decay time curves analysis. The efficiency and mechanism of energy transfer are investigated carefully. Moreover, due to the non-concentration quenching property of K3Tb(PO4)2, the photoluminescence spectra of K3Tb1−x(PO4)2:xCe3+ are studied and the results show that when x = 0.11 the strongest Tb3+ green emission can be realized.

Characterization and luminescence of Eu/Sm-coactivated CaYAl3O7 phosphor synthesized by using a combustion method

A novel red-emitting phosphor, CaYAl3O7: Eu3+, Sm3+, is synthesized by a combustion method at a low temperature (850°), and the single phase of CaYAl3O7 is confirmed by powder X-ray diffraction measurements. The photoluminescence property results reveal that the red emission intensity of Eu3+ is strongly dependent on the Sm3+ concentration. Only the Eu3+ luminescence is detected in the Eu3+-Sm3+ co-doped CaYAl3O7 phosphor with 393 nm excitation. However, under the characteristic excitation (402 nm) of Sm3+, not only the Sm3+ emission but also the Eu3+ emission are observed. A possible mechanism of the energy transfer between Sm3+ and Eu3+ is investigated in detail.

Spectroscopic properties and mechanism of Tm3+/Er3+/Yb3+co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals

Transparent Tm3+/Er3+/Yb3+ co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals are prepared. Under excitation of a 980-nm laser diode (LD), compared with the glass before heat treatment, the Tm3+/Er3+/Yb3+co-doped oxyfluorogermanate glass ceramics can emit intense blue, green and red up-conversion luminescence and Stark-split peaks; X-ray diffraction (XRD) and transmission electron microscope (TEM) results show that BaF2 nanocrystals with an average diameter of 20 nm are precipitated from the glass matrix. Stark splitting of the up-conversion luminescence peaks in the glass ceramics indicates that Tm3+, Er3+ and (or) Yb3+ ions are incorporated into the BaF2 nanocrystals. The up-conversion luminescence intensities of Tm3+, Er3+ and the splitting degree of luminescence peaks in the glass ceramics increase significantly with the increase of heat treat temperature and heat treat time extension. In addition, the possible energy transfer process between rare earth ions and the up-conversion luminescence mechanism are also proposed.

Photoluminescence characteristics and energy transfer between Bi3+ and Eu3+ in Na2O—CaO—GeO2—SiO2 glass

We report the photoluminescence (PL) of Eu3+-doped glass with Bi3+ as a sensitizer. The specific glass system with the strong enhancement of the red emission of Eu3+ is obtained by adding a small number of Bi3+ ions instead of increasing the Eu3+ concentration. The emission band of Bi3+ overlaps with the excitation band of Eu3+ and the lifetime decay curves, resulting in a very efficient energy transfer from Bi3+ to Eu3+. The probability of energy transfer is strongly dependent on Bi3+ concentration. In addition, the intensity of 4f–4f transition is much stronger than that of a charge-transfer (CT) band in the excitation spectrum, which indicates that the Na2O—CaO—GeO2-SiO2 glass is a suitable red-emitting phosphor with high stability as a candidate for light-emitting diodes (LEDs).

Up-conversion luminescence properties and energy transfer of Er3+/Yb3+ co-doped oxyfluoride glass ceramic containing CaF2 nano-crystals

The Er3+/Yb3+ co-doped transparent oxyfluoride glass-ceramics containing CaF2 nano-crystals were successfully prepared. After heat treatments, transmission electron microscopy (TEM) images showed that CaF2 nano-crystals of 20–30 nm in diameter precipitated uniformly in the glass matrix. Comparing with the host glass, high efficiency upconversion luminescence of Er3+ at 540 nm and 658 nm was observed in the glass ceramics under the excitation of 980 nm. Moreover, the size of the precipitated nano-crystals can be controlled by heat-treatment temperature and time. With the increase of the nano-crystal size, the intensity of the red emission increased more rapidly than that of the green emission. The energy transfer process of Er3+ and Yb3+ was convinced and the possible mechanism of Er3+ up-conversion was discussed.

Zn 2+ 掺杂诱导Eu 3+ 激活BiOCl层状半导体的反常发光性能研究

采用固相法在500℃下成功制备Zn 2+ 掺杂BiOCl:Eu 3+ 层状半导体, 并研究了Zn 2+ (0~20mol%)掺杂对Eu 3+ 激活BiOCl层状半导体发光性能的影响。利用X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电镜(SEM)、傅里叶变换红外光谱(FT-IR)、激发–发射光谱、荧光寿命衰减曲线对样品的结构和性能进行表征。研究发现, 随Zn 2+ 掺杂浓度增大, BiOCl晶体结构不变, Eu 3+ 荧光寿命延长, 但发光强度却出现先减后增的反常现象。综合分析表明这可能与BiOCl特殊的层状结构有关。通过XRD和XPS的表征可以推断: 当Zn 2+ 掺杂浓度≤10mol%, Zn 2+ 在BiOCl中掺杂方式以晶胞层间隙掺杂为主; 当Zn 2+ 掺杂浓度>10mol%后, 掺杂方式逐渐向取代掺杂转变。两种掺杂机制对Eu 3+ 荧光寿命的改变以及形成缺陷对基质能量传递效率的影响可能是形成上述反常现象的主要原因。研究结果有助于认识稀土掺杂层状半导体的发光性能及影响规律, 并对Eu 3+ 掺杂BiOCl这类新型发光材料的开发设计具有指导意义。

Yb 3+ -Tm 3+ 共掺BiOBr纳米晶的近红外上转换发光特性研究

采用水热法合成了Yb 3+ -Tm 3+ 共掺BiOBr纳米晶, 研究了其上转换发光性能。在980 nm光激发下, 样品中Tm 3+ 离子实现了 3 H 4 → 3 H 6 、 1 G 4 → 3 F 4 和 1 G 4 → 3 H 6 跃迁, 进而发出强烈的近红外光(801 nm)和较弱的红光(655 nm)与蓝光(485 nm)。探讨了样品的上转换发光机理, 上转换发光强度与激发功率的关系表明在980 nm激发下Tm 3+ 的蓝光和红光发射为三光子过程, 而近红外发光为双光子过程。随着Yb 3+ 浓度增加, 近红外发光显著增强, 近红外光与蓝光( I 801 nm / I 485 nm )的发光强度比高达71.4。研究结果表明, Yb 3+ -Tm 3+ 共掺BiOBr纳米晶在生物荧光标记领域具有潜在的应用前景。