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All-inorganic lead halide perovskites have been extensively studied in the past several years due to their superior stability against moisture, oxygen, light, and heat compared with their organic–inorganic counterparts. CsPbBr3 with suitable band gap and ultrahigh photoluminescence quantum yield is a promising candidate for pure green emitter in the backlighting display to fill the so-called “green gap.” Here, vapor-phase growth of CsPbBr3 microspheres is reported for highly efficient pure green light emission. The as-synthesized microspheres exhibit a stronger photoluminescence (PL) intensity with a photoluminescence quantum yield of 75% resulting from the lower energy of longitudinal optical phonons revealed by temperature dependent PL studies. Importantly, with the diameter increasing from 2 to 50 μm the PL peak positions of the microspheres can be readily tuned from 527 to 539 nm, well filling the so-called “green gap.” The red-shift with increasing diameter can be ascribed to the reabsorption process during the photon propagation inside the microspheres. The studies provide a route to improve the photoluminescence quantum yield in all-inorganic lead halide perovskites, but also suggest an alternative approach to achieve the pure green emission for the backlighting display.