Due to the low solubility of BaF2, the BaTiF6:Mn4+ phosphor for whitelight-emitting diodes application has been generally synthesized by the hydrothermal route, during which process the valence of the manganese dopant is difficult to be controlled as tetravalent. In this paper, a new synthesis method that proceeded at room temperature was reported. This method uses BaTiOF4 as the precursor and allows for the control of the phase transformation rate from BaTiOF4 to BaTiF6 in the K2MnF6/HF acid solution. Benefitting from that, we successfully prepared red-emitting BaTiF6:Mn4+ elongated crystals with a single-crystal nature up to a record-breaking length of 200–300 μm. The effects of the crystallinity of the BaTiOF4 precursor on its phase transformation rate into BaTiF6 and on the optimal Mn4+ doping concentration were studied. The BaTiF6:Mn4+ single-crystal phosphor exhibits relatively excellent hydrolysis-resistant behavior after being immersed in water for 3 h, at which condition the commercial K2SiF6:Mn4+ has become brown. This study may inspire the room-temperature preparation of other hydrolysis-resistant alkali earth fluorotitanate or fluorosilicate phosphors with stable tetravalent manganese doping.
Lu-Ri Bao,Jing-Ze Zhang,Wei-Ping Tang,Shu-Ying Sun
The Mn-based Li 1.6 Mn 1.6 O 4 ion sieve is among the most effective lithium adsorbents due to its high lithium-ion adsorption capacity and selectivity for Li-ions. However, the inherent disadvantages of manganese dissolution and low structural stability prevent its industrial application. In this study, a series of Li 1.6 Mn 1.6 O 4 @R were synthesized by the low temperature solid phase hydrothermal method that exhibit highly anti-dissolution properties for the lithium adsorption from brine water. The LMO-L, LMO-LM, and LMO-M adsorbents show great adsorption capacities of 46.0 mg g −1 , 43.0 mg g −1 , and 38.0 mg g −1 compared to the 42.3 mg g −1 for the pristine adsorbent. After 20 cycles the dissolution loss of Mn was 0.06 % of LMO-L adsorbents. This improvement in adsorption properties is attributed to the stabilized layered structure due to the evolution of oxygen during the coating reaction, and the inhibition of the interfacial side reactions between the solution and the adsorbent by metal oxide coating. X-ray diffraction, and X-ray photoelectron spectroscopy analysis indicate the formation of Li 2 MnO 3 on the material surface, which can increase tetravalent manganese on the surface. Furthermore, our work may provide new insights for the design of efficient Mn-based adsorbents with high stability for water treatment applications.
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