Violet phosphorus is another promising layered semiconducting elemental structure for electronic and optoelectronic applications. Violet phosphorus quantum dots (VPQDs) have unique optical and electronic properties due to quantum mechanics. However, the VPQDs are still unexplored since the structure of violet phosphorus and preparation of violet phosphorene have just been confirmed recently. The preparation and property investigation of VPQDs are urgent. A simple solvothermal method has been developed to effectively synthesize VPQDs. The size and fluorescence intensity of VPQDs are adjustable according to solvothermal parameters. An average lateral size of 3.16 ± 0.78 nm and an average height of 1.81 ± 0.57 nm (monolayer) have been obtained by the as-produced VPQDs, giving intense green fluorescence with excellent optical stability under conditions such as UV light irradiation, ionic strength, and pH environments. The VPQDs have also been demonstrated to be an effective fluorescent probe to selectively detect Cu²⁺ ions in the organic phase with a linear range of 10–300 μg mL⁻¹ and a detection limit as low as 19.6 nM. The VPQDs are also promising nanostructures for photovoltaic materials, photocatalysts, photodetectors, or labeling live biological materials.