The control of surface properties of all inorganic cesium lead halide perovskite (CsPbX3; X = Cl, Br, or I) quantum dots (QDs) is essential to achieve excellent stability and high photoluminescence quantum yields (PLQYs). Herein, a facile method was performed to simultaneously enhance the stability and PLQYs of CsPbX3 QDs by a ZnX2/hexane solution post-treatment. We show that the halogen defect on the surface of CsPbX3 QDs can be treated in a controlled way, whereby the “black dots” that adhered on the surface as observed by transmission electron microscopy have be completely removed, resulting in enhanced stability and photoluminescence. The PLQYs of CsPbCl3, CsPbBr3, and CsPbI3 increased from 4, 58, and 63% to 86, 93, and 95%, respectively, and the origin of the “black dots” as well as their transformation mechanism has been demonstrated. As a result, the poly(dimethylsiloxane) composite films created by encapsulating stable and nearly defect-free green-emitting CsPbBr3, the red-emitting K2SiF6:Mn4+ phosphor, and a blue emission GaN chip were prepared and used to fabricate a remote-type white light-emitting diode device, which exhibits a high luminescence efficiency (≤98 lm/W) and a wide color gamut (∼130% of the National Television Standard Committee standard), suggesting the potential for liquid crystal display backlight application.