Li Chengyu

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.

Reddish orange long lasting phosphorescence of Sm3+ in Sr2ZnSi2O7:Sm3+ phosphors

Abstract Long lasting phosphorescence phosphors with composition of (Sr 1- x Sm x ) 2 ZnSi 2 O 7 were prepared by conventional high-temperature solid-state method. Their properties were systematically investigated utilizing XRD, photoluminescence, phosphorescence and thermoluminescence spectra. The results showed that these phosphors emitted reddish orange light that corresponds to the characteristic emission due to the 4 G 5/2 → 6 H 5/2 , 6 H 7/2 and 6 H 9/2 transitions of Sm 3+ . After the UV light excitation source was switched off, the bright reddish orange long lasting phosphorescence could be observed and it could last for about 30 min in the limit of light perception of dark-adapted human eyes (0.32 mcd/m 2 ). A wide TL band raging from room temperature to 700 K with two dominating peaks at 340 and 602 K appeared in the TL spectrum. The TL curve could be fitted to five TL peaks and the low temperature TL peak at 340 K was found to be responsible for the long lasting phosphorescence. Also, the mechanism was discussed.

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.

Luminescence properties of a new yellow long-lasting phosphorescence phosphor NaAlSiO4:Eu2+,Ho3+

Abstract A new aluminosilicate long-lasting phosphor with composition of NaAlSiO 4 :Eu 2+ ,Ho 3+ was synthesized and investigated. Under UV light excitation, the phosphor emitted yellow light corresponding to the characteristic emission of Eu 2+ due to 5d-4f transition. Bright yellow phosphorescence sustaining for more than 30 min was observed after ceasing the excitation. The phosphorescence intensity decay obeyed a t −1 decay law, indicating a tunneling electron-hole recombination process in the phosphor. Four peaks appeared in the thermoluminescence curve and the ones at 322 and 370 K were thought to account for the long lasting phosphorescence at room temperature. The Ho 3+ ion incorporated into the phosphor did not give any light but dramatically increased the intensities of both photoluminescence and phosphorescence via promoting defect levels in the phosphor.

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.

Luminescent properties of blue long-lasting phosphorescence phosphors Sr6Al18Si2O37:Eu2+,RE3+

Abstract A series of novel blue long-lasting phosphorescence phosphors Sr 6 Al 18 Si 2 O 37 :Eu 2+ ,RE 3+ (RE 3+ =Ho 3+ , Gd 3+ , Dy 3+ and Pr 3+ ) were prepared by the conventional high-temperature solid-state reaction in a reductive atmosphere. Their properties were systematically investigated utilizing X-ray diffraction (XRD), photoluminescence, phosphorescence and thermoluminescence (TL) spectra. The phosphors emitted blue light that was related to the emission of Eu 2+ due to 5d-4f transition. Bright blue long-lasting phosphorescence (LLP) could be observed after the excitation source was switched off. For the optimized sample, the blue long-lasting phosphorescence could last for nearly 4 h in the light perception of the dark-adapted human eye (0.32 mcd/m 2 ). The effects of RE 3+ ions on phosphorescence properties of the phosphors were studied, and the results showed that the co-doping of RE 3+ ions greatly enhanced the intensity of the peak around 315 K which was related to the long lasting phosphorescence of the phosphors at room temperature and consequently improved the performance of the blue phosphorescence such as intensity and persistent time.

Long Lasting Phosphorescence in Eu2+ and Ce3+ Co-Doped Strontium Borate Glasses

Long lasting phosphorescence (LLP) was observed in Eu2+, Ce3+ co-doped strontium borate glasses prepared under the reducing atmosphere due to the emission of both Eu2+ and Ce3+. The methods of photoluminescence, thermoluminescence and phosphorescence were used to study the samples, and possible mechanism was suggested. The co-doping of Ce3+ ions poisoned the phosphorescence emission of Eu2+ because of the competition to obtain the trapped electron. The phosphorescence of Ce3+ in the sample decays more quickly than that of Eu2+, which is suggested for the reason that the emission energy of Ce3+ is higher or the distance between Ce3+ and electron traps of the glasses is longer.

Research progresses of lanthanide sulfides

Lanthanide sulfides are one kind of important functional materials with abundant structures and peculiar properties, which have wide applications in many fields, such as inorganic pigments, thermoelectric materials, optical materials and magnetic materials, etc al., and become one of the hot research topics in the world in recent years. In this review article, the synthesis methods and application research progresses of the lanthanide sulfides are summarized and commented, especially the structures, properties and applications of the g-Ln2S3. Several comments on the problems existed in the research of lanthanide sulfides had been given out, and the development trends in this field are proposed.