Long-lasting Phosphorescence Spectra Research Articles

Photoluminescence and afterglow of Mn2+ doped lithium zinc silicate

Novel green emitting long lasting phosphorescence (LLP) Li1.14Zn1.43SiO4:Mn2+ (LZS: Mn2+) was prepared successfully through a conventional solid-state reaction. Phase purity was checked by X-ray diffraction. The photoluminescence and afterglow properties of as-prepared phosphors were studied systematically by diffuse reflectance spectra, photoluminescence spectra, decay curves, afterglow spectra and thermoluminescence glow curves measurements. The photoluminescence spectra and LLP spectra indicated that LZS: Mn2+ phosphors exhibits green emission center at 526nm originated from 4T1→6A1 transition of Mn2+. The duration of Mn2+ doped Li1.14Zn1.43SiO4 phosphors can last about 1h. Thermoluminescence glow curves indicated that the LLP of LZS: Mn2+ phosphor was generated by the suitable trap depth. Based on the experimental results, a model was constructed to discuss the mechanism of afterglow briefly.

A novel green long-lasting phosphorescence phosphor Ca14Mg2(SiO4)8:Eu2+, Dy3+

A novel silicate long-lasting phosphorescence phosphor Ca14Mg2(SiO4)8:Eu2+, Dy3+ was prepared by high-temperature solid state reaction. Its properties were investigated systematically by powder X-ray diffraction patterns, Rietveld refinements, photoluminescence spectra, long-lasting phosphorescence spectra, phosphorescence decay curves, and thermoluminescence spectra. Under the excitation of 400nm, Ca14Mg2(SiO4)8:Eu2+, Dy3+ phosphor exhibits green light with the peak at 505nm, which is attributed to the 4f65d1–4f7 electronic transition of Eu2+ ions. It is also found that Ca14Mg2(SiO4)8:Eu2+, Dy3+ phosphor can emit green persistent phosphorescence after the irradiation of ultraviolet or visible light is stopped. And for the optimal sample, the green persistent luminescence can last for about half an hour. The co-doping of Dy3+ ions greatly enhances the intensity and duration of the persistent luminescence in Ca14Mg2(SiO4)8:Eu2+, Dy3+ phosphor. However, the peak position of the long-lasting phosphorescence spectrum is red shift compared to that of the photoluminescence spectrum, and the possible reason was analyzed. Meanwhile, the long-lasting phosphorescence mechanism of this phosphor was also discussed.

Luminescence properties of a new bluish green long-lasting phosphorescence phosphor Ca9Bi(PO4)7:Eu2+,Dy3+

A new long-lasting phosphorescence phosphor Ca9Bi(PO4)7:Eu2+,Dy3+ was synthesized by solid state reaction and its long-lasting phosphorescence properties were investigated for the first time. The X-ray powder diffraction, photoluminescence, long-lasting phosphorescence spectra, decay curves and thermoluminescence curves were measured. The Ca9Bi(PO4)7:Eu2+,Dy3+ phosphor exhibits an asymmetric emission centered at 475nm, which can be ascribed to the 4f65d1–4f7 electronic transition of Eu2+. For the optimized sample, the bright bluish green long-lasting phosphorescence could be observed for 5h by naked eyes after the excitation source was removed. The long-lasting phosphorescence spectra show that the co-doping of Dy3+ ions greatly enhance the intensity of the long-lasting phosphorescence. Meanwhile, the long-lasting phosphorescence mechanism of this phosphor was discussed. Based on our study, Dy3+ ions are suggested to increase the density of electron or hole traps so as to improve the performance of the bluish green phosphorescence of Eu2+, including the intensity and persistent time.

Luminescence properties of white-light long-lasting phosphor Y 2 O 2 S:Dy 3+ , Mg 2+ , Si 4+

A series of novel Y 2 O 2 S:Dy 3+ , Mg 2+ , Si 4+ white-light long-lasting phosphors were synthesized by the solid-state reaction method. The Y 2 O 2 S:Dy 3+ , Mg 2+ , Si 4+ phosphors were characterized by X-ray diffraction, photoluminescence and long-lasting phosphorescence spectra, and thermoluminescence curves. The samples doped with different concentrations of Dy 3+ ions were composed of the pure Y 2 O 2 S phase. Under 357 nm UV excitation, the emission peaks at 486 nm and 577 nm were assigned to the 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 transitions of Dy 3+ respectively. When Dy 3+ concentration was 1%, the CIE chromaticity diagram was (0.28, 0.28), and the decay time could last for over 36 min (≥1 mcd/m 2 ).

Sol–gel synthesis of long-lasting phosphors CdSiO3: Mn2+, RE3+ (RE = Tb, Eu, Nd) and luminescence mechanism research

Mn2+ and RE3+ (RE=Tb, Eu, Nd) co-doped CdSiO3 orange phosphors were prepared at 1050°C by a sol–gel method. The phase and crystallinity of the synthesized materials were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The luminescence characteristics were analyzed using photoluminescence (PL) spectra, afterglow decay curves, long-lasting phosphorescence spectra, and thermoluminescence (TL) spectra. Due to the difference in co-doped rare earth ionic radii, it varied greatly in trap density and trap depth caused by the different defects deriving from RE3+ ions co-doping into the CdSiO3: Mn2+ host. The afterglow intensity and time for these samples increased as follows: CdSiO3: Mn2+0.2%, Nd3+0.8%<CdSiO3: Mn2+0.4%, Tb3+0.8%<CdSiO3: Mn2+0.4%, Eu3+0.3%. CdSiO3: Mn2+0.4%, Eu3+0.3% had the best afterglow properties, which could be due to the proper traps formed by Eu3+ ions co-doping into the host. The role of RE3+ co-doped into the CdSiO3: Mn2+ matrix and the possible long-lasting phosphorescence process was also discussed in this paper.

Energy transfer and excitation wavelength dependent long-lasting phosphorescence in Pr 3+ activated Y 3Al 5O 12

Long-lasting phosphorescence (LLP) was observed in Pr 3+-doped Y 3Al 5O 12 (YAG:Pr) after it was excited by 240 or 290 nm light. The photoluminescence (PL) and LLP properties were studied. It is interesting that the PL and LLP spectra were different. In the PL emission spectra both the emissions of d–f and f–f transitions of Pr 3+ ions were observed. However, in the LLP spectra of YAG:Pr the emissions of d–f transition were absent. It is deduced that the differences were due to the energy transfer process between traps and emission centers. On the other hand, significant differences were observed between the two LLP spectra after the sample was excited by 240 and 290 nm lights, respectively. The thermoluminescence (TL) properties were also studied. It is suggested that these studies will be significant for understanding the mechanism of LLP phenomenon.

Long-lasting phosphorescence study on Y 3Al 5O 12 doped with different concentrations of Ce 3+

Long-lasting phosphorescence (LLP) was observed in Ce-doped Y 3Al 5O 12 phosphors synthesized in reducing atmosphere. The characteristic emission of the 2D- 2F 5/2 and 2D- 2F 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 2D- 2F 5/2 and 2D- 2F 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.