Zhengfa Hu

Synthesis and luminescent properties of Eu3+ and Dy3+ doped BiPO4 phosphors for near UV-based white LEDs

The phosphors BiPO4:Eu3+ co-doped with Dy3+ were synthesized by the conventional solid-state reaction method. XRD and scanning electron microscopy results showed that the crystalline phase of the samples BiPO4:Eu3+ transforms from high-temperature monoclinic phase to low-temperature monoclinic phase with the increase of Dy3+ concentration. The photoluminescence properties of the samples showed that the colors shifting from red–orange area to blue–green area are close to those of ideal white light by readjusting the doping concentration ratio of Eu3+ and Dy3+. The Eu3+and Dy3+ doped BiPO4 phosphors may be potential applications in white light near-UV light-emitting diodes.

Persistent luminescent and photocatalytic properties of ZnxGa2O3+x (0.8 ≤ x ≤ 1) phosphors

The ZnxGa2O3+x (x = 1, 0.95, 0.9, 0.85, 0.8) phosphors were synthesised successfully via high temperature solid-state reaction. The photoluminescent, persistent luminescent and photocatalytic properties of the phosphors had been studied systematically. The results indicated that their excitation and emission spectra were similar to those of ZnGa2O4 phosphors and all of them have excellent persistent luminescent and photocatalytic properties. The optical properties were changed with the ratio of the Zn2+/Ga3+ and the Zn0.85Ga2O3.85 phosphor showed the best persistent luminescent and photocatalytic properties. The Zn0.85Ga2O3.85 phosphor can be effectively activated by an ultraviolet lamp and ultraviolet excitation can lead to 10 min of persistent green emission. Moreover, the Zn0.85Ga2O3.85 could provide more defect energy levels which can act as photogenerated electron traps and maintain the electron–hole pairs for a longer period, enhancing the persistent luminescent and photocatalytic performance.

Enhanced persistent luminescence and photocatalytic properties of Ga 2 O 3 :Cr 3+ by In 3+ doping

Ga2O3:Cr3+, In3+ phosphors, synthesized via a high temperature solid state reaction, exhibit photocatalytic activity and persistent luminescence. With substituting In3+ for Ga3+ in Ga2O3:Cr3+, the duration of near-infrared (NIR) persistent luminescence was prolonged obviously at room temperature under 254 nm ultraviolet (UV) excitation and the photocatalytic activity was highly improved. The emission and excitation spectra indicated that In3+ doping has no obvious effect on peak positions of Ga2O3:Cr3+. The thermoluminescence (TL) curves showed that a new suitable trap was introduced into Ga2O3:Cr3+ by In3+ doping. It was considered that photocatalytic activity and persistent luminescence properties are highly associated. What’s more, the new trap plays an important role for capturing photo-generated electrons or holes, which is highly responsible for the high separation of photo-generated electron-hole pairs and could improve the persistent luminescence and photocatalytic properties of Ga2O3:Cr3+ effectively.

Influence of co-doping Si ions on persistent luminescence of ZnGa 2 O 4 : Cr 3+ red phosphors

The impact of the addition of some amount of SiO2 in the ZnGa2O4:Cr3+ phosphors have been studied onto its persistent luminescent performance. The ZnGa2O4:Cr3+ phosphors with different Si4+ concentrations have been synthesized by using conventional solid-state reaction method. The X-ray diffractive patterns, photoluminescence (PL), thermoluminescence (TL) and afterglow decay have been measured and analyzed. The experimental results indicated that all the phosphors with different Si4+ codopant have the characteristic emission of Cr3+ and the co-doped Si4+ intensifies emission of N2 line and R lines. Furthermore the persistent luminescence was improved in both intensities and decay rates, in which the phosphor with 1mol% Si4+ has the best TL and the appropriate trap depth leading to the good persistent performance.

Enhanced photocatalytic activity and persistent luminescence in Zn2GeO4:Mn2+ by Eu3+ doping

Zn2GeO4:Mn2+,Eu3+ and Zn2GeO4:Mn2+ powders were synthesized by a high-temperature solid-state reaction. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the structures and morphologies of the synthesized powders, respectively. The photocatalytic properties and long persistent luminescence performance were improved by Eu3+ doping. Thermoluminescent (TL) curves showed that the trap concentration in the material was increased with Eu3+ doping, which formed trap centers in Zn2GeO4:Mn2+. The trap centers can capture the electrons or holes and subsequently increase the separation of photogenerated electrons and holes by suppressing the recombination of captured electrons and holes; thus, resulting in an improved photocatalytic activity and a prolonged persistent luminescence. The present strategy may be used as a general method to improve the photocatalytic activity and persistent luminescence.

Enhancing persistent luminescence and photocatalytic properties in Ti as a trap center in ZnGa2O4

ZnGa2O4 and ZnGa2O4:Ti phosphors were synthesized by the solid state method, and their persistent luminescence and photocatalytic properties were investigated in detail. The results of this study showed that Ti4+ doping improved the persistent luminescence properties. Thermoluminescence measurements demonstrated that the trap concentration considerably increased upon incorporation of Ti4+ ions into the ZnGa2O4 lattice. The traps generated by Ti doping were responsible for improvement in persistent luminescence. Furthermore, photocatalytic activity tests showed that the Ti-doped ZnGa2O4 phosphor exhibited much higher photocatalytic activity than the ZnGa2O4 host. UV–Vis diffuse reflectance spectra demonstrated that Ti-doped ZnGa2O4 shown a higher UV absorption efficiency. A comparison between the density of states of ZnGa2O4:Ti and ZnGa2O4 revealed that the bottom of the conduction band was modified by Ti doping. Hence, it could be concluded that Ti doping enhanced light harvest capability to generate more electron–hole pairs, and acted as a trap center by decreasing the recombination of photogenerated electrons and holes, resulting in the enhancement of both persistent luminescence and photocatalytic activity.

Persistently luminescent and photocatalytic properties of ZnGa2O4 phosphors

The phosphors ZnGa2O4 were synthesized via high temperature solid-state reaction. The crystal structure, photoluminescence, persistent luminescence, and photocatalytic properties of ZnGa2O4 were studied in detail. The x-ray diffraction patterns showed that some remaining phases of ZnO and β-Ga2O3 appeared with the excess amount of ZnO and Ga2O3, respectively. The results of the Raman spectra indicated that the first order Raman active modes of ZnGa2O4 were attributed to O2− ions and Zn2+ ions in tetrahedral sites. The phosphors exhibited a broad-band emission around 430 nm, which could be ascribed to the Ga–O transition of regular octahedral sites in the spinel lattice of ZnGa2O4. It also exhibited the emission peak around 430 nm shift to longer wavelength with the amount of the excess ZnO. The persistent luminescence of ZnGa2O4 could be observed for 10 min by naked eyes at room temperature under 254 nm ultraviolet (UV) excitation. In addition, photocatalytic activity test showed that ZnGa2O4 exhibited excellent photocatalytic activity for the degradation of Rhodamine B by the UV irradiation. It was indicated that the traps played an important role in trapping the electrons or holes to decrease the combination of the holes or electrons producing by the irradiation.

Enhanced persistent luminescence of Zn 2 GeO 4 host by Ti 4+ doping

Zn2GeO4 and Zn2Ge1−xO4:xTi4+ powders were synthesized by high temperature solid-state reaction method. X-ray diffraction was used to characterize the structure. The photoluminescence and persistent luminescence properties of Zn2Ge1−xO4:xTi4+ phosphors were characterized by the excitation spectra, the emission spectra and the persistent decay curves. The results showed that the Ti4+ doping prolonged the persistent luminescence period of the Zn2GeO4 host. The thermoluminescence and absorption spectra indicated that a new defect band was formed by Ti4+ doping, which was ascribed to photoreduction of Ti4+ to Ti3+. The new defect band, which is located between the conduction band and valence band close to bottom of the conduction band, can capture the electrons to decay the electrons recombining with holes resulting in a prolonged persistent luminescence.

Luminescence and cathodoluminescent properties of monoclinic Y2WO6 co-doped with Dy-Bi

Dy-Bi co-doped yttrium tungstate crystal materials were synthesized by high temperature solid-state method. To reveal the photoluminescence features and properties of the samples, some measurements have been taken. It turned out that different Bi3+ concentrations play obvious influence in emission performance, and show visible light emission under ultraviolet light excitation. Besides, the effect of temperature on phase structure of samples has also been studied here. Superhigh X-ray luminescence of the phosphors exhibited the promising application in the field of high energy detection. The X-ray irradiation crystal resistance stability of the phosphors has also been investigated through the subsequent testing of XRD and spectra.