Double-Matrix Encapsulation of Cyan Perovskite Nanomaterials for High-Efficiency Full-Spectrum White Light-Emitting Diodes

White light-emitting diodes (WLEDs) have become essential to various aspects of our daily lives. However, the absence of a strong cyan emission significantly hinders the development of full-spectrum WLEDs that could achieve high-quality applications. Here, a feasible method is introduced to synthesize highly luminescent and stable CsPbBr3 by employing an efficient dual-matrix encapsulation technique. Sodium citrate (SC) is utilized as a matrix to disperse these CsPbBr3 nanomaterials, thereby reducing self-absorption and energy transfer. In addition to functioning as a matrix, SC also passivates the perovskite nanomaterials, resulting in an increased photoluminescence quantum yield (PLQY) and enhanced stability of the perovskite. Notably, the stability of the perovskite, especially its resistance to water, is significantly enhanced after encapsulating the composite within poly(methyl methacrylate) (PMMA). A series of full-spectrum WLEDs with variable color temperatures ranging from 2763 to 7145 K and high color rendering indices (90–96) were fabricated using SC-CsPbBr3@PMMA in combination with commercially available YAG and red phosphors CaAlSiN3:Eu2+. This research opens up new avenues for the utilization of perovskite nanomaterials in the development of next-generation full-visible-spectrum WLED lighting.