Mimicking the oxygen evolution center Making a synthetic analog of plant photosynthesis is a key goal for exploiting solar energy and replacing fossil fuels. Zhang et al. synthesized a manganese-calcium cluster that looks and acts like the oxygen evolution center in photosystem II (see the Perspective by Sun). The mimic structurally resembles the biological complex, with the notable exception of bridging protein ligands and water-binding sites on a dangling Mn atom. Functionally, however, the cluster's metal center readily undergoes four redox transitions, which contribute to splitting water into oxygen. This and other synthetic mimics will pave the way for developing more efficient catalysts for artificial photosynthesis. Science , this issue p. 690 ; see also p. 635

Single-mode laser is realized in a cesium lead halide perovskite submicron sphere at room temperature. All-inorganic cesium lead halide (CsPbX, X = Cl, Br, I) microspheres with tunable sizes (0.2-10 μm) are first fabricated by a dual-source chemical vapor deposition method. Due to smooth surface and regular geometry structure of microspheres, whispering gallery resonant modes make a single-mode laser realized in a submicron sphere. Surprisingly, a single-mode laser with a very narrow line width (∼0.09 nm) was achieved successfully in the CsPbX spherical cavity at low threshold (∼0.42 μJ cm) with a high cavity quality factor (∼6100), which are the best specifications of lasing modes in all natural nano/microcavities ever reported. By modulating the halide composition and sizes of the microspheres, the wavelength of a single-mode laser can be continuously tuned from red to violet (425-715 nm). This work illustrates that the well-controlled synthesis of metal cesium lead halide perovskite nano/microspheres may offer an alternative route to produce a widely tunable and greatly miniaturized single-mode laser.

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