Lihong Jiang

Sr1.7Zn0.3CeO4: Eu3+ Novel Red-Emitting Phosphors: Synthesis and Photoluminescence Properties

A series of novel red-emitting Sr1.7Zn0.3CeO4:Eu(3+) phosphors were synthesized through conventional solid-state reactions. The powder X-ray diffraction patterns and Rietveld refinement verified the similar phase of Sr1.7Zn0.3CeO4:Eu(3+) to that of Sr2CeO4. The photoluminescence spectrum exhibits that peak located at 614 nm ((5)D0-(7)F2) dominates the emission of Sr1.7Zn0.3CeO4:Eu(3+) phosphors. Because there are two regions in the excitation spectrum originating from the overlap of the Ce(4+)-O(2-) and Eu(3+)-O(2-) charge-transfer state band from 200 to 440 nm, and from the intra-4f transitions at 395 and 467 nm, the Sr1.7Zn0.3CeO4:Eu(3+) phosphors can be well excited by the near-UV light. The investigation of the concentration quenching behavior, luminescence decay curves, and lifetime implies that the dominant mechanism type leading to concentration quenching is the energy transfer among the nearest neighbor or next nearest neighbor activators. The discussion about the dependence of photoluminescence spectra on temperature shows the better thermal quenching properties of Sr1.7Zn0.3CeO4:0.3Eu(3+) than that of Sr2CeO4:Eu(3+). The experimental data indicates that Sr1.7Zn0.3CeO4:Eu(3+) phosphors have the potential as red phosphors for white light-emitting diodes.

Sr9Mg1.5(PO4)(7):Eu2+: A Novel Broadband Orange-Yellow-Emitting Phosphor for Blue Light-Excited Warm White LEDs

A new orange-yellow-emitting Sr9Mg(1.5)(PO4)7:Eu(2+) phosphor was prepared via high-temperature solid-state reaction. The structure and optical properties of it were studied systematically. Sr9Mg(1.5)(PO4)7:Eu(2+) can be well-excited by 460 nm blue InGaN chips and exhibit a wide emission band covering from 470 to 850 nm with two main peaks centered at 523 and 620 nm, respectively, which originate from 5d-4f dipole-allowed transitions of Eu(2+) in different crystallographic sites. The sites attribution, concentration quenching, fluorescence decay analysis, and temperature-dependent luminescence properties were investigated in detail. Furthermore, a warm white LED device was fabricated by combining a 460 nm blue InGaN chip with the optimized orange-yellow-emitting Sr9Mg(1.5)(PO4)7:Eu(2+). The color coordinate, correlated color temperature and color rendering index of the fabricated LED device were (0.393, 0.352), 3437 K, and 86.07, respectively. Sr9Mg(1.5)(PO4)7:Eu(2+) has great potential to serve as an attractive candidate in the application of blue light-excited warm white LEDs.

Tunable long lasting phosphorescence due to the selective energy transfer from defects to luminescent centres via tunnelling in Mn2+ and Tm3+ co-doped zinc pyrophosphate

A series of new phosphors Zn2(0.97-x)P2O7:0.06Tm(3+),2xMn(2+) (0 ≤ x ≤ 0.05) were synthesized and their luminescence properties were investigated. The results showed that the defects in all the phosphors were related to Tm(3+), and Mn(2+) merely served as the emission centres. Tm(3+) also acted as an emission centre and yielded blue phosphorescence corresponding to its characteristic f-f emissions in the phosphors where the Mn(2+) concentration was low (x ≤ 0.001), while in the phosphors with high concentrations of Mn(2+) it mainly served as a defect by forming Tm. The electrons thermally released from defects selectively transferred to Mn(2+) centres mainly through thermally-assisted tunnelling and this resulted in their red to near-infrared phosphorescence. By adjusting the ratio of Mn(2+) to Tm(3+) to control the spectral distribution, tunable long lasting phosphorescence from blue to near-infrared was achieved.

Long-lasting phosphorescence study on Y3Al5O12 doped with different concentrations of Ce3+

Abstract Long-lasting phosphorescence (LLP) was observed in Ce-doped Y 3 Al 5 O 12 phosphors synthesized in reducing atmosphere. The characteristic emission of the 2 D- 2 F 5/2 and 2 D- 2 F 7/2 transition of Ce 3+ in photoluminescence (PL) and LLP spectra was studied. It was interesting that the ratio between the peak areas of 2 D- 2 F 5/2 and 2 D- 2 F 7/2 transitions in the PL spectrum was different from the ratio of that in LLP emission spectrum. And the ratios had different change regularities with increased Ce 3+ concentration. The possible reason was attributed to the defect in the YAG host, which was affected by increasing the Ce 3+ concentration. There were indications that the defect in the Ce 3+ -doped YAG samples was strongly associated with oxygen vacancy. And the defect levels were studied through thermoluminescence (TL) experiment. The results showed that the trap depth was between 0.6 and 0.65 eV, and the kinetic order of the LLP was 2.

Thermoluminescence characteristics of NaSr4(BO3)3:Ce3+ under β-ray irradiation

Abstract The thermoluminescence (TL) properties of Ce 3+ doped NaSr 4 (BO 3 ) 3 phosphor under the β-ray irradiation were reported. The polycrystalline sample was synthesized by high temperature solid-state reaction. The TL glow curve of NaSr 4 (BO 3 ) 3 :Ce 3+ phosphor was composed of only one peak. TL kinetic parameters of NaSr 4 (BO 3 ) 3 :Ce 3+ were deduced by the peak shape method, the activation energy ( E ) was 0.590 eV and the frequency factor was 1.008×10 6 s −1 . TL dose response was linear in the range of measurement. The 3-dimensional (3D) TL emission spectrum was also recorded, the emission spectrum consisted of two bands located at 441 and 479 nm respectively, corresponding to the characteristic 4f 0 5d 1 → 2 F (5/2 , 7/2) transitions of the Ce 3+ ion. The fading behavior of the NaSr 4 (BO 3 ) 3 :Ce 3+ phosphor over a period of 15 d was also studied.

Highly transparent ytterbium doped yttrium lanthanum oxide ceramics

Abstract To prepare ytterbium doped lanthania yttria nanopowder a method of laser evaporation of mixed oxides was used. After calcinations of the powder at 1200 °C a pure single-phase solid solution Yb 3+ :(La x Y 1− x ) 2 O 3 was formed in the nanoparticles. Influence of lanthanum oxide as an isovalent additive on the yttria structure was investigated. The lanthanium ions were proved to be a good aid to sinter yttria ceramics doped with Yb 3+ at moderate temperatures about 1650 °C. The ceramics with relative density higher than 99.99% and grain size about 40 μm were fabricated. Full transmittance of 1.8 mm thick Yb 0.11 La 0.23 Y 1.66 O 3 ceramics reached 82.5% at 800 nm. This material could be a good gain medium for ytterbium high power pulse lasers.

Investigation of a novel color tunable long afterglow phosphor KGaGeO4:Bi3+: luminescence properties and mechanism

Although a variety of Bi3+-activated common luminescent materials have been investigated, few Bi3+-doped long afterglow phosphors have been discovered up to now. In this work, we developed a novel long afterglow material KGaGeO4:Bi3+ by solid-state reaction. The highlight of this work is the observation of bright cyan to blue color tunable long afterglow of KGaGeO4:Bi3+. The structural information of the samples was studied in detail using Rietveld refinement. Photoluminescence and phosphorescence properties of the phosphor were investigated systematically. The reason why the photoluminescence and phosphorescence color can be tuned has been discussed. A bright long afterglow could be observed by the naked eye for 3 hours in the dark after ultraviolet irradiation was ceased. Moreover, we have analyzed the reason why the KGaGeO4 host is suitable for Bi3+ to generate afterglow emission by exploring the nature of traps in KGaGeO4:Bi3+ with the help of thermoluminescence spectra. In this phosphor, Bi3+ ions doped in K+ sites behave as luminescence centers, while negatively charged defects serve as hole-trapping centers. In view of the experimental results, a feasible afterglow mechanism of KGaGeO4:Bi3+ was also proposed and discussed.

Luminescence properties of a novel reddish orange long-lasting phosphorescence phosphor Zn2P2O7:Sm3+,Li+

In this article we synthesized a series of new reddish orange long-lasting phosphorescence phosphors by co-doping Li+ ions into Sm3+ activated α-Zn2P2O7, characterized their luminescence properties, and evaluated the effect of Li+ co-doping on both photoluminescence and Phosphorescence. The results showed that both the photoluminescence and Phosphorescence originated from characteristic reddish orange emissions of Sm3+ from its 4f–4f transitions of 4G5/2–6H5/2, 4G5/2–6H7/2 4G5/2–6H9/2 and 4G5/2–6H11/2. Besides markedly enhancing the photoluminescence intensity of Sm3+, the Li+ entering into the crystal lattice also promoted the long lasting phosphorescence performance via modifying the defect levels in the phosphors. The optimal long afterglow material was achieved when the Li+ concentration is 2 mol%. This phosphor shows bright reddish orange phosphorescence which could last for more than 3 hours in the dark. Four peaks appeared in its thermoluminescence curve, and the one at around 350 K was proved to be responsible for the occurrence of long lasting phosphorescence. The release of the captured electrons in the defect levels corresponding to this TL peak in room temperature to emission centers of Sm3+ underwent a tunneling process.

Fabrication and Luminescence Study of Ce 3+ -doped YAG Transparent Ceramics: Fabrication and Luminescence Study of Ce 3+ -doped YAG Transparent Ceramics

0.3at% Ce∶YAG(Y3Al5O12) transparent ceramics was fabricated by a solid state reaction method,with the high pure(≥99.99%) commercial powders α-Al2O3,Y2O3,CeO2 using as raw materials.The ceramic green bodies were sintered in 1750℃ for 10h in vacuum.The linear transmission of the prepared Ce∶YAG ceramics in visible range 500-900nm reaches about 80% homogeneously(1.2mm thick,double polished).Photoluminescence properties show that the emitting band of the Ce∶YAG ceramics lies in 500-700nm,which is the characteristic emitting of Ce3+.It is concluded that the Ce∶YAG transparent ceramics is a promising scintillator materials especially for middle-low energy ray detecting.

Synthesis and photoluminescence properties of novel red-emitting Ca14Mg2(SiO4)8:Eu3+/Sm3+ phosphors

Abstract Novel red-emitting Eu3+, Sm3+ singly doped and co-doped Ca14Mg2(SiO4)8 phosphors were prepared by conventional solid- state reaction. Powder X-ray diffraction patterns were employed to confirm phase purity. Ca14Mg2(SiO4)8:Eu3+ phosphors exhibited intense red emission under 394 nm excitation and Ca14Mg2(SiO4)8:Sm3+ phosphors, excited at 405 nm, also showed strong red emitting at 602 nm. The concentration quenching mechanism of Ca14Mg2(SiO4)8:Eu3+ was dipole-dipole interaction, while that of Ca14Mg2(SiO4)8:Sm3+ was energy migration among nearest neighbor ions. The results indicated that Ca14Mg2(SiO4)8:Eu3+ and Ca14Mg2(SiO4)8:Sm3+ were promising red-emitting phosphors for WLEDs. Meanwhile, the effect of co-doping Sm3+ ions on photoluminescence properties of Ca14Mg2(SiO4)8:Eu3+ was studied and energy transfer from Sm3+ to Eu3+ was discovered in Eu3+, Sm3+ co-doped phosphors.