Qinhua Wei

Combinatorial optimization of La, Ce-co-doped pyrosilicate phosphors as potential scintillator materials.

A combinatorial method was employed to rapidly screen the effects of La, Ce-co-doping on the luminescent properties of Gd2Si2O7 pyrosilicate using an 8 × 8 library. The candidate formulations (Gd1-x-yLax)2Si2O7:Ce2y were evaluated by luminescence pictures under ultraviolet excitation. The optimal composition was found to be (Gd0.89La0.1)2Si2O7:Ce0.02 after scaled-up preparation and detailed characterization of powder samples, which shows an excellent light output under both ultraviolet and X-ray excitation (about 5.43 times of commercial YAG:Ce powders). The XRD results indicate that the phase structure sequence is tetragonal-orthorhombic-triclinic for different calcination temperatures and doping ions. The (Gd0.89La0.1)2Si2O7:Ce0.02 powder sample also demonstrated excellent temperature stability of luminescence up to 200 °C and a short decay time of several tens of nanoseconds, suggesting that this may represent a new kind of scintillation material, such as single crystals, ceramics, glass, or phosphors.

Combinatorial discovery of self-color-mixing phosphors Bi4(1−x)Si3O12:RE4x3+ (RE3+ = Dy3+, Eu3+) for direct white light emission

Phosphors with direct white light emission have been successfully found in the rare earth doped bismuth silicate systems, Bi4(1−x)Si3O12(BSO) : RE4x3+ (RE3+ = Eu3+, Dy3+), using a fast combinatorial design and screening method. The material libraries were synthesized by ink-jetting precursor solutions into microreactor wells and sintering at high temperatures. The candidate compositions of the white light phosphors with varied dopant concentrations were evaluated by screening the recorded luminescence pictures under UV light excitation. The optimal compositions showing white light emission were further confirmed to be Bi3.96Si3O12 : Eu0.043+ and Bi3.84Si3O12 : Dy0.163+ via scale-up experiments. Additionally, the CIE chromaticity coordinate of the white light emission is located at (0.333, 0.326) for the optimal Bi3.96Si3O12 : Eu0.043+ and the CIE coordinate of the Bi3.84Si3O12 : Dy0.163+ phosphor is located at (0.302, 0.333), which are both very close to the CIE coordinate of soft sunlight (0.330, 0.330) and good for human eyesight. For the BSO : RE3+ (RE3+ = Eu3+, Dy3+) samples, the generation of direct white light emission can be realized by properly controlling the amount of doped RE3+ ions. It has been concluded that the white light emission directly results from a self-color-mixing mechanism of intrinsic host luminescence and doping ion luminescence. Besides that, the luminescence properties, energy transfer mechanism, and decay time of the direct white light phosphors have been discussed to set up a close relationship between the doping compositions and luminescence characteristics of the BSO : RE3+ (RE3+ = Eu3+, Dy3+) phosphors.

Preparation and luminescence properties of SiO2/Lu2Si2O7:Ce composite starting from mesopore template

A chemical processing method has been developed for preparing the nanosized phosphors of Lu2Si2O7:Ce3+ (LPS:Ce) by choosing mesoporous template SBA-15 as Si source. Accordingly, the luminescent ceramic composite of SiO2/LPS:Ce has also been densified by hot pressing at elevated temperatures using composited powders with the prepared LPS:Ce phosphor particles embedded in SiO2 matrix. XRD analysis and TEM observation have been carried out for both the prepared LPS:Ce phosphors and the final SiO2/LPS:Ce ceramics, indicating complete crystallization and a well distribution of LPS:Ce nanoparticles in SiO2 component. The ultra-violet fluorescence spectra, X-ray excited luminescence spectra, and decay time of the resultant SiO2/LPS:Ce ceramic composite have also been measured, showing a blue emission from Ce3+ and a fast decay time of about 37 ns. Experimental results show that an attractive strategy has been successfully developed for producing translucent or even transparent ceramics with phosphor nanoparticles embedded in matrix. The specific route can provide an effective control of reaction channels and a uniform distribution of phosphor particles in matrix by the template guiding role from ordered mesoporous SiO2. The fabrication method thus developed could be employed in other kinds of composited ceramics.

Preparation and Luminescence Properties of

Bi4Si3O12:Zn2+(BSO:Zn) polycrystalline powders were successfully prepared by sol-gel method. X-ray diffraction measurements confirm that the Zn2+-doped materials are all monophasic solid solution powders. The influences of doping concentration on the photoluminescence and radioluminescence characteristics have been investigated and discussed. The Zn2+ doped material shows a better light yield than that of undoped material under X-ray excitation. The fluorescence decay time of the optimal material, excited by UV has been aslso measured. The results show that the Zn2+ ion doping has a positive effect on the light yield of BSO. But the crystal growth and characterizations of BSO:Zn polycrystalline powders prepared deserve further investigations.