Yi Zhang,Cuiping Zhou,Qifeng Zhang,Pengfei Yin,Xiyuan Sun,Kaiming Wang,Jian Wang,Xing Feng
In this paper, a synthesized material change from perovskite-layer-structured La 2 Ti 2 O 7 to perovskite type LaTiO 3 induced by Li 2 CO 3 addition was observed. The [TiO 6 ] octahedral site symmetry and particle uniformity showed an obvious variation with the change from La 2 Ti 2 O 7 to LaTiO 3 . A broadband far-red emission from 670 to 780 nm emerged when Mn 4+ , Li + ions were co-doped. Furthermore, (Mn 4+ , Li + ) co-doped LaTiO 3 phosphor can be effectively excited by near-UV and blue lights, which is suitable for combining with commercial InGaN LED chips. The LaTiO 3 :0.4%Mn 4+ , 150%Li + phosphor exhibited a high quantum efficiency of 71.1% and a good thermal stability with emission intensity retained 65% at 423 K. Finally, a LED device was fabricated with the LaTiO 3 :0.4%Mn 4+ , 150%Li + phosphor, which matches well with the absorption of photochrome of P FR and shows a good potential for use in agricultural cultivation fields.
Mengyang Xia,Ben Chong,Xiangjiao Gong,Hang Xiao,He Li,Honghui Ou,Bin Zhang,Guidong Yang
Using solar energy to fix N2 and produce NH3 is a promising route. For nitrogen photofixation, the transition-metal active site in the low oxidation state is conducive to the adsorption of N2, but it is often difficult to further dissociate N2, restricting the reaction. Therefore, it is necessary to precisely modulate the electron energy level of the active site to couple with the molecular orbitals of N2, thus reducing the energy barrier of N2 dissociation. Here, the perovskite-type LaTiO3–x with an ultralow oxidation state Ti2+ site is achieved via in situ modulation of phase transition and defect engineering. The obtained Ti2+ sites could inject more d-orbital electrons into the N2 π* antibonding orbitals to achieve N2 activation and dissociation. Therefore, compared with pristine La2Ti2O7 and La2Ti2O7–x samples without ammonia production activity, LaTiO3–x samples showed a remarkable performance for photocatalytic N2 fixation. The NH3 generation rate reached up to 107 μmol gcat–1 h–1 after the 1st hour, and the average NH3 generation rate after 4 h was approximately 51.5 μmol gcat–1 h–1. Furthermore, in situ characterization and density functional theory (DFT) calculations revealed the role of Ti sites with different oxidation states (Ti4+, Ti3+, Ti2+) in N2 activation, which would provide a unique perspective for designing efficient N2 fixation catalysts.
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