M-type strontium ferrite is a kind of magnetic functional material with wide application prospect. In this work, SrFe 12− x Al x O 19 (0 ≤ x ≤ 1) and Sr 1− y Ca y Fe 8 Al 4 O 19 (0 ≤ y ≤ 0.4) have been prepared by a hydrothermal method, and the effects of Al 3+ doping and Al 3+ and Ca 2+ co-doping on the magnetic properties have been investigated. X-ray diffraction analysis indicates all the samples are a hexagonal structure, and the shift of the diffraction peaks suggests that Al 3+ and Ca 2+ are successfully doped in SrFe 12 O 19 . Field emission scanning electron microscope images show the particles have the hexagonal shape with the size of 1.1–2.9 µm. Vibrating sample magnetometer reveals that the doping of Al 3+ and the co-doping Al 3+ and Ca 2+ can enhance magnetic properties of strontium ferrite. For example, the values of coercivity and the saturation magnetization of SrFe 8 Al 4 O 19 are 914.1 Oe and 44.0 emu/g, which are 3% and 117% enhancement compared with SrFe 12 O 19 , respectively. For Sr 1− y Ca y Fe 8 Al 4 O 19 , coercivity and saturation magnetization increase from 914.1 Oe and 41.8 emu/g to 1047.2 Oe and 50.2 emu/g when the Ca 2+ doping concentration increases from 0 to 0.4. Moreover, the effects of acid washing also on phase composition, morphology and magnetism are researched. The as-synthesized doping strontium ferrite will be useful for the applications in security switching and recording media.
Kaiyuan Deng,Yahong Jin,Lifang Yuan,Haoyi Wu,Yihua Hu
Phosphor-converted light-emitting diode (pc-LED) technology, as artificial lighting source, is the most promising option for providing power for plant growth in future smart agricultural factories. However, developing red phosphors with the desired emission spectral range and good thermal stability is still experimental. In this study, an Mn 4+ -doped BaZrGe 3 O 9 red-emitting phosphor with remarkable thermal stability is reported. The red emission, spanning the wavelength range of 600–800 nm, matches the absorption range of chlorophyll a, b and phytochrome (P r ). Its good thermal stability at 150 °C is in addition to its emission intensity, which is 81.7 % of its room-temperature intensity. Co-doping with Ca 2+ contributes to a 1.7-fold increase in the red emission intensity at room temperature. The encapsulation of the present phosphor onto UV LED chips produces red emitting LED devices, which can be used for garlic and corn cultivation. The implementation reveals that the six-hour artificial red light illumination supplement is the most effective and significant means to promote garlic and corn growth. The as-obtained red-emitting phosphor may be a promising candidate for pc-LEDs promotion of crop growth in agricultural factories.
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