Mixed-dimensional (2D + nD, n = 0, 1, and 3) heterostructures opened up a new avenue for fundamental physics studies and applied nanodevice designs. Herein, a novel type-II staggered band alignment CuFe₂O₄/MoS₂ mixed-dimensional heterostructures (MHs) that present a distinct enhanced (20–28%) acetone gas sensing response compared with pure CuFe₂O₄ nanotubes are reported. Based on the structural characterizations and DFT calculation results, the tentative mechanism for the improvement of gas sensing performance of the CuFe₂O₄/MoS₂ MHs can be attributed to the synergic effect of type-II band alignment and the MoS₂ active sites.

Low activator concentration in upconversion phosphors has been a hindrance in improving luminescence performance. Herein, we report an Er3+ doping concentration as high as 30 at. % in the CaLuAlO4 upconversion host. The CaLuAlO4:Er3+ phosphors were prepared by the traditional high-temperature solid-state method. Under the excitation of a 980 nm laser, the optimal concentration of Er3+ approaches 30% according to the total integrated intensity of red and green upconversion luminescence. This quenching concentration is one order of magnitude higher than that in the traditional Er3+ doped upconversion polycrystals. The results obtained from first-principles calculations suggest that there are no in-plane or chain rare-earth ions in the cell. This increases the difficulty of propagating excitation energy to quench centers and is advantageous for high doping concentration. Our work can spark people's interest in the research and application of highly doped upconversion phosphors.