Jipeng Fu

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.

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.

A convenient and efficient synthesis method to improve the emission intensity of rare earth ion doped phosphors: the synthesis and luminescent properties of novel SrO:Ce3+ phosphor

Convenient, efficient synthesis methods that improve the emission intensity of rare earth ion doped phosphors are relatively rare. In this study, a simple modified solid-state reaction is proposed. This approach can greatly improve reaction temperature and overcome the requirement for harsh conditions. Its advantages come from the substitution of a solid–solid interface for a solid–gas interface. A novel Ce3+ doped SrO phosphor with an enhancive bright cyan emission is prepared and the photoluminescent properties of SrO:Ce3+ are first reported. This study will provide valuable clues for synthesizing many other ion doped functional materials besides rare earth ion doped luminescent materials.

Investigation on Luminescence Properties of a Long Afterglow Phosphor Ca2SnO4:Tm3+

A series of new long afterglow phosphors Ca2 SnO4:xTm(3+) were synthesized by using traditional solid-state reactions. XRD measurements and Rietveld refinement revealed that the incorporation of the Tm(3+) dopants generated no second phase other than the original one of Ca2 SnO4, which indicated that the dopants completely merged into the host. The corresponding optical properties were further systematically studied by photoluminescence, phosphorescence, and thermoluminescence (TL) spectroscopy. The results show that the Tm(3+)-related defects account for the bright bluish green afterglow emission from the characteristic f-f transitions of Tm(3+) ions. The bluish green long-lasting phosphorescence could be observed for 5 h by the naked eye in a dark environment after the end of UV irradiation. Two TL peaks at 325 and 349 K from the TL curves were adopted to calculate the depth of the traps, which were 0.45 and 0.78 eV, respectively. The mechanism of the long afterglow emission was also explored.

Single-phased white-light-emitting Ca₄(PO₄)₂O:Ce³⁺,Eu²⁺ phosphors based on energy transfer.

A novel single-composition Ca4(PO4)2O:Ce(3+),Eu(2+) phosphor emitting white light was synthesized by conventional solid-state reaction for light-emitting diode applications. X-ray diffraction, photoluminescence spectra, and luminescence decay spectra were used to characterize the samples. Energy transfer from Ce(3+) to Eu(2+) ions was observed in the co-doped samples, and the transfer mechanism in the Ca4(PO4)2O:Ce(3+),Eu(2+) phosphors was dipole-dipole interaction. The emission hue of Ca4(PO4)2O:Ce(3+),Eu(2+) was found to vary from blue (0.165, 0.188) to white (0.332, 0.300) and eventually to orange (0.519, 0.366) by precisely controlling the ratio of Ce(3+) to Eu(2+). The combination of a 380 nm near-ultraviolet chip with a Ca4(PO4)2O:0.02Ce(3+),0.012Eu(2+) phosphor produced a diode emitting white light with ultra-wideband emission and a correlated color temperature of 4124 K. Overall, results indicated that the prepared samples may be potentially applied in white-light-emitting diodes.