Intrinsic Cool White-to-Deep Blue Emission in a Mechanically Tunable Zero-Dimensional Zirconium Halide Phosphor

Single component white-light emitters with cool-white emission are highly desirable, yet metal halide perovskites of this kind remain rare. Traditionally, white-light emission is achieved by combining blue and yellow phosphors, incurring efficiency losses. We present a zero-dimensional zirconium halide phosphor, (PPh₄)₂ZrCl₆ (PPh₄⁺: tetraphenylphosphonium cation), exhibiting intrinsic cool-white-light emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.33, 0.33) at 320 nm excitation with a correlated color temperature (CCT) of 5609 K, closely aligning with ideal white-light standards. The isolated [ZrCl₆]^2- octahedra induce a strong exciton binding energy of 358.7 meV, along with dual emission bands from singlet and triplet self-trapped excitons (STEs), which are tunable via the excitation wavelength. With increasing pressure up to 9 GPa, the emission band at 442 nm intensifies at the expense of 610 nm emission. Mechanical force shifts the emission from cool white to deep blue, shifting the CIE coordinates to (0.19, 0.18) for fully crushed crystals, due to a gradual reduction in the density of states near the Fermi level and the sharpening of band edges. Our findings establish (PPh₄)₂ZrCl₆ single crystals as promising white-light phosphors with tunable properties, offering new insights into single-component emitters and stimuli-responsive photoluminescent materials.