Preparation And Near-infrared Luminescence Of Fluorescent Material With Ni²⁺in The Octahedral Local Environments

Transparent Ni2+-doped ZnO-MgO-Al2O3-SiO2(ZMAS)system galss-ceramics containing zinc/magnesium spinel solid solution as crystalline hosts were prepared.And the heat treatment conditions and optical properties of the materials were studied.The new borate materials of the CdO-MO-B2O3(M=Zn,Mg,Ni)system were explored and the luminescence properties were examined.(1)Transparent Ni2+-doped ZMAS system glass-ceramics with broadband infrared luminescence were prepared by heat-treatment of parent glass via melt quenching method.According to the DTA results,the glass transition temperature(Tg)and maximum crystallization temperature(Tc)of the as-prepared samples are 754? and 948?,respectively.The glass-ceramics obtained from two different heat-treatment systems were characterized by X-ray diffraction,and the crystallization behaviors and phase transitions were analyzed.The results show that transparent Ni2+-doped spinel-phase glass-ceramics can be obtained by using two-step heat-treatment process.(2)The coordination environment of Ni2+ in the crystal field of prepared glass-ceramics was investigated by the ultraviolet-visible absorption spectra.The results indicate that tetrahedral and octahedral sites Ni2+ ions coexist in spinel microcrystals of Ni2+-doped ZMAS system glass-ceramics.The fluorescence spectrum test shows that the broadband infrared luminescence centered at 1324nm with full width at half maximum(FWHM)of about 490nm was observed from the samples.The mechanism of these phenomena is attributed to the transitions of 3T2g(3F)?3A2g(3F)of octahedral six-folded Ni2+ in the solid solution of spinel structure of Zn/MgAl2O4.(3)The nucleation mechanism of transition-metal Ni2+-doped ZMAS system glass-ceramics samples was studied mainly by two methods.a.The glass melts were cooled slowly to different specified temperatures and precipitates occurs.The microstructure and phase composition of the precipitates were studied;b.The precursor glass samples were kept at 800? for 0.5h,1h,1.5h,2h,and 3h respectively,crystal phase changes in the glass were analyzed by X-ray diffraction.The results show that in the early stage of nucleation,titanate phase was first precipitated in the glass matrix,which induced the nucleation and growth of spinel.With the extension of time,titanate phase disappeared and the spinel was retained.The addition of the nucleating agents dose not affect on the composition of the main crystal phase of the transparent glass-ceramics.(4)In this paper,the crystals of Cd2.42Zn0.5B2O6 and Cd2MgB2O6 which found by our research group previously were re-prepared via high-temperature solid-phase method and further studied,respectively.Through comparing the crystal structures of the new compound Cd2.42Zn0.58B2O6 with the known borates ?-Cd3B2O6 and ?-Cd3B2O6,the connection modes of BO3 triangles and the cationcentered polyhedra of the three compounds are discussed,and the optical diffuse reflectance spectrum of Cd2.422Zn0.58B2O6 indicates an optical band gap of 3.96 eV,corresponding to the UV cut-off wavelength 313 nm.It is believed that this work could give a meaningful guide to explore new borate compounds.It was found that both Cd2+ and Mg2+ occupy six coordination sites in the crystal of Cd2MgB2O6.NiO was doped in a certain proportion of Cd2MgB2O6 samples for Mg2+ radius(r=0.072nm)is close to Ni2+ radius(r=0.069nm),which were expected to produce near-infrared luminescence.This provides a new idea for the further study of glass-ceramics with the botate substance as the main crystalline phase that can produce near-infrared luminescence.