Physical, structural and optical studies on magnesium borate glasses doped with dysprosium ion

Intense visible emissions from dysprosium(Dy3+) ions doped glasses became prospective for diverse technological applications. In this paper, physical, optical and structural properties of magnesium borate glasses doped with varied concentrations of DyOwere examined. Such glasses were synthesised by melt quenching method and characterized at room temperature using several analytical techniques.Luminescence and absorption spectra(in the visible region) of as-quenched samples were used to evaluate the physical and optical properties. XRD pattern confims the amorphous state of as-quenched samples. The Fourier transform infrared(FTIR) spectra of glasses reveal various bonding vibrations assigned to different functional groups. UV-vis-NIR spectra disclose eight absorption bands accompanied by a band for hypersensitive transition positioned at 1260 nm(~6 H→~6 F). The values of direct and indirect optical energy band gap of the studied glasses are decreased with the increase of Dyion contents. The photoluminescence spectra of all glasses under the excitation of 380 nm display two prominent emission bands centred at 497 nm(~4 F→~6 H, blue) and 587 nm(~4 F→~6 H, green).The achieved intense luminescence from the proposed glass composition may be beneficial for solidstate laser applications.

Synthesis of Mg_2B_2O_5 whiskers via coprecipitation and sintering process

Mg2B2O5 whiskers with high aspect ratio were synthesized by coprecipitation and sintering process using MgCl2-6H2O, H3BO3, and NaOH as raw materials and KCl as a flux. Their formation process was investigated by thermogravimetry and differential scanning calo- rimetry （TG-DSC）, X-ray diffraction （XRD）, and scanning electron microcopy （SEM）. It is found that the products synthesized at 832℃ are monoclinic Mg2B205 whiskers with a diameter of 200-400 nm and a length of 50-80 μm. Transmission electron microscopy （TEM） and selected area electron diffraction （SAED） analyses show that the whiskers obtained at 832℃ are single crystalline and grow along with the [010] direction. The growth mechanism of Mg2B2O5 whiskers was also presented.

Hierarchical porous MgBO_2(OH) microspheres: Hydrothermal synthesis,thermal decomposition, and application as adsorbents for Congo red removal

A facile eco-friendly hydrothermal route （180 ℃, 12.0 h） has been developed for the first time to the uniform hierarchical porous MgBO2（OH） microspheres without the aid of any organic additive, surfactant or template, by using the abundant MgCl2·6H2O, H3BO3 and NaOH as the raw materials. The as-obtained porous microspheres exhibit a specific surface area of 94.752 mg·g-1, pore volume of 0.814 cm3.g-1, and ca. 84.0% of which have a diameter of 2.25-3.40 μm. The thermal decomposition of the porous MgBO2（OH） microspheres （650 ℃, 2.5 ℃. min-l） leads to the porous Mg2B2O5 rnicrospheres with well-retained morphology. When utilized as the adsorbents for the removal of CR from mimic waste water, the present porous MgBO2（OH） microspheres exhibit satisfactory adsorption capacity, with the maximum adsorption capacity qm of 309.1 mg-g-1, much higher than that derived from most of the referenced adsorbents. This opens a new window for the facile green hydrothermal synthesis of the hierarchical porous MgBO2（OH） microspheres, and extends the potential application of the 3D hierarchical porous metal borates as high-efficiency adsorbents for organic dyes removal.

Comparison of thermoluminescence spectra of MgB_4O_7 doped with dysprosium and manganese

A series of magnesium borate phosphors MgB4O7：Dy, MgB4O7：Mn and MgB4O7：Dy,Mn were prepared and their ther-moluminescence （TL） emission spectra were measured. TL emission bands in 480, 575 and 660 nm at 200 and 360 oC were observed in the MgB4O7：Dy due to the transitions of the trivalent rare earth ions Dy3＋. The glow peaks of broad wavelength band around^580 nm at 180 and^290 oC were observed in MgB4O7：Mn due to the emission of Mn2＋ions. The main glow peak of MgB4O7 co-doped with Dy and Mn appeared in 580 nm at^360 oC. When MgB4O7 was co-doped with Dy （0.5 mol.%） and different concentrations of Mn （0.01 mol.%-1.0 mol.%）, the peak in 580 nm at 360 °C was intensified and broadened as the concentration of Mn increased, while the peaks in 480, 680 and 750 nm below 300 °C remained the characteristic emission of Dy3＋and were reduced in intensity. The emission spectra of the MgB4O7：Dy,Mn phosphor showed that the competitive de-excitation processes between Dy3＋and Mn2＋existed and the energy transfer occurred from Dy3＋to Mn2＋. These results meant that rare earth and Mn ions in MgB4O7：Dy,Mn might cause the formation of defects complex that dominated the traps and recombination.