hui Xu

Highly dispersive {001} facets-exposed nanocrystalline TiO2 on high quality graphene as a high performance photocatalyst

A series of composites of nanocrystalline TiO2 with exposed {001} facets and high quality graphene sheets (GS) were synthesized via a one-step hydrothermal reaction in an ethanol–water solvent. The obtained {001} facets-exposed TiO2/GS photocatalysts were characterized by Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction pattern (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet visible (UV-vis) diffuse reflectance spectroscopy (DRS) and Electrical Impedance Spectroscopy (EIS). They showed a better photocatalyst properties than P25 and other normal TiO2/GS composites, which could be explained on the basis of the formation of chemical Ti–O–C bond and the formation of nano-sized Schottky interfaces at the contacts between TiO2 and GS. The influence of the exposed {001} facets on the photocatalytic activity was investigated. The result showed that positively charged dye molecules are preferentially adsorbed onto the TiO2/GS composites due to the photogenerated charge gathered on GS. Overall, this work could provide new insights into the fabrication of TiO2–carbon composites as high performance photocatalysts and facilitate their application in addressing environmental protection issues.

Design, synthesis and characterization of an orange-yellow long persistent phosphor: Sr 3 Al 2 O 5 Cl 2 :Eu 2+ ,Tm 3+

A novel orange-yellow emitting Sr3Al2O5Cl2:Eu(2+), Tm(3+) phosphor with bright and long persistent luminescence (LPL) has been newly developed. The incorporation of Tm(3+) into the Sr3Al2O5Cl2:Eu(2+) as an auxiliary activator dominates its long persistent luminescence and thermoluminescence characteristics to a large extent. The emissions in Sr3Al2O5Cl2:Eu(2+), Tm(3+) for both fluorescence and LPL are due to the 5d → 4f transitions of Eu(2+). The orange-yellow long persistent luminescence with the chromaticity coordination of (0.53, 0.46) can persist for nearly 220 min at recognizable intensity level (≥ 0.32 mcd/m2). This investigation provides a new and efficient long persistent phosphor which enriches the color of the existing LPL.

Effect of oxygen vacancies on the red phosphorescence of Sr 2 SnO 4 :Sm 3+ phosphor

We reported the synthesis of a novel red long-afterglow material Sr(2)SnO(4):Sm(3+). Comparing with the air-sintered sample, a significant enhancement in both the fluorescence and phosphorescence for the vacuum-sintered sample was observed. This improvement could be attributed to the increase of oxygen vacancies which act as the sensitizer and the electron traps for the effective energy transfer from Sr(2)SnO(4) host to Sm(3+). The defects act as traps were investigated with thermoluminescence. For the presence of deep stable traps able to immobilize the energy permanently at room temperature, the Sr(2)SnO(4):Sm(3+) could be considered as a potential storage phosphor as well.

The persistent luminescence and up conversion photostimulated luminescence properties of nondoped Mg2SnO4 material

The nondoped Mg2SnO4 material with inverse spinel structure was synthesized by solid state reaction. This phosphor showed a broad green emission band covering 470–550 nm under 291 nm excitation, which was due to the recombination of F centers with holes. Stimulated by 980 nm infrared laser, the green photostimulated luminescence was first observed in a nondoped oxide. After ultraviolet irradiation, the green persistent luminescence of Mg2SnO4 could be seen in darkness for about 5 h. The decay curves revealed that the long persistent luminescence was governed by tunneling mechanism and it proved the presence of different trap clusters in Mg2SnO4. These trap clusters (such as [SnMg••–Oi″], [SnMg••–2e′], and [SnMg••–e″]) induced the trap levels with different depths in band gap and corresponded to the three components (at 110, 168, and 213 °C) of the thermoluminescence glow curve of Mg2SnO4. These trap levels with different depths were proved to be not independent. It revealed that the shallow traps (110 °C)...

Ce3 + , Dy3 + Co-Doped White-Light Long-Lasting Phosphor: Sr2Al2SiO7 Through Energy Transfer

White-light long-lasting phosphor Sr2Al2SiO7:Ce3+,Dy3+ was prepared by a high temperature solid-state reaction. The energy transfer between Ce3+ and Dy3+ was systematically investigated. Through co-doped Ce3+ and Dy3+, the duration of the persistent luminescence of Sr1.975Al2SiO7:Ce-0.005,Dy-0.03 reached nearly 50 min. The decay curves and thermoluminescence spectra were used to characterize what kind of trap existed in the sample. A possible afterglow mechanism was presented and discussed. This work provides a promising approach for the development of white-light long-lasting phosphor

Luminescence and Storage Properties of Sm-Doped Alkaline-Earth Atannates

The thermoluminescence, persistent luminescence and storage properties of Sm-doped alkaline-earth stannates, A(2)SnO(4):Sm3+ (A=Ca, Sr, Ba), are studied above room temperature. Different characteristic features of the thermoluminescence glow curves of A(2)SnO(4):Sm3+ are observed, which implicates A(2)SnO(4):Sm3+ could provide different potential applications. Ca2SnO4:Sm3+ with suitable traps shows efficient persistent luminescence, the red persistent luminescence could be observed in the dark for about several hours. Sr2SnO4:Sm3+ possesses relative deep traps fulfill the requirement of a good storage phosphor, and the different amount of the stored energy could be released under the various treatments (the excitation with 980/680 nm light or heating at 200 degrees C). The extremely weak PL intensity of Ba2SnO4:Sm3+ implies that it is inadequate applied as storage phosphor or afterglow phosphor. The decay time of afterglow increase in the order of Ba2SnO4:Sm3+ < Sr2SnO4:Sm3+ < Ca2SnO4:Sm3+. Our analysis indicates that the persistent luminescence properties of A(2)SnO(4):Sm3+ are governed by the cation vacancy, serve as the hole trap, which accept one hole to get stabilized

Investigation of the role of silver species on spectroscopic features of Sm3+-activated sodium–aluminosilicate glasses via Ag+-Na+ ion exchange

The introduction of silver into the Sm3+-doped sodium–aluminosilicate glasses prepared by Ag+-Na+ ion exchange leads to the formation of different ionic silver species. Under 270 nm/250 nm excitation, effective enhancement of Sm3+ luminescence is ascribed to radiative energy transfer from isolated Ag+ to Sm3+. Under 355 nm excitation, white light emission was realized by combining red orange light emission of Sm3+ with green light emission of Ag+-Ag+ and blue light emission of (Ag2)+. Silver nanoparticles formed by further heat treatment are effective quenchers of luminescence from the corresponding excited states of Sm3+ ions.

Fluorescence and phosphorescence properties of new long-lasting phosphor Ba 4 (Si 3 O 8 ) 2 :Eu 2+ , Dy 3+

A novel long-lasting phosphorescence (LLP) material Ba4(Si3O8)2:Eu2+, Dy3+ with high chemical stability was achieved successfully. Two emission centers (Eu (I) and Eu (II)) were found in Ba4(Si3O8)2 due to the substitution of Eu2+ in different Ba2+ sites. Both 
Eu (I) and Eu (II) had contribution to the afterglow process, however, the decay rate of Eu (I) was higher than that of Eu (II). Ba3.982(Si3O8)2: 0.008Eu2+, 0.01Dy3+ exhibited a long-lasting phosphorescence whose duration was more than 24 h. Through the analysis of the thermoluminescence (TL) curves, we found that Eu2+ single doped Ba4(Si3O8)2 has a possibility to be a kind of storage phosphor. This work provides a new and efficient candidate for LLP and storage materials.

Self-activated long persistent luminescence from different trapping centers of calcium germanate.

Ca2Ge7O16 phosphor with a self-activated LPL was synthesized. The unique emission of Ca2Ge7O16 related to the creation of the oxygen vacancies was proved. With increasing concentration of Nd3+, the LPL peaks in these phosphors red-shift obviously, which results in the corresponding emitting color changing from purple to blue. The thermoluminescence spectra indicate that there are two different types of traps, which are attributed to oxygen and calcium vacancies, respectively. Both of them not only act as the trapping centers, but also as the exciton energy-level involved in the emission process. Accordingly, the mechanism of the LPL process was discussed briefly.

Enhanced Long-Persistence of Sr2MgSi2O7 : Eu2 + , Dy3 + Phosphors by Codoping with Ce3 +

Sr 2 MgSi 2 O 7 samples doped with Ce 3+ , Eu 2+ , (Eu 2+ , Ce 3+ ), (Eu 2+ , Dy 3+ ), and (Eu 2+ , Dy 3+ , Ce 3+ ) were prepared and studied. The Ce 3+ 5d-4f emissions from two Sr 2+ sites in Sr 2 MgSi 2 O 7 were observed. However, only one single emission band at 466 nm was found in Sr 2 MgSi 2 O 7 :Eu 2+ . The energy transfer from Ce 3+ to Eu 2+ in Sr 2 MgSi 2 O 7 was demonstrated to be a multipolar interaction. It was found that Sr 2 MgSi 2 O 7 :Ce 3+ showed no afterglow. Sr 2 MgSi 2 O 7 :Eu 2+ showed some afterglow with a short persistence, and its afterglow could be enhanced by the incorporation of Ce 3+ . The triply doped phosphor Sr 2 MgSi 2 O 7 :Eu 2+ , Dy 3+ , Ce 3+ exhibited higher brightness and longer lasting time than that of Sr 2 MgSi 2 O 7 :Eu 2+ , Dy 3+ , which could be ascribed to more traps formed by the incorporation of Ce 3+ .