Sulfide Quantum Dot Band-Gap Comparator (2D)

Sulfide nanocrystals — CdS, ZnS and PbS — are the workhorse quantum dots behind QLED displays, quantum-dot solar cells and infrared photodetectors, and every one of their optical properties starts from a single size-dependent equation. This 2D companion implements the same Brus equation as the 3D version — real bulk band gap, electron/hole effective masses and dielectric constant for each compound — but graphs it directly: E_g(R) is plotted live against radius, a marker rides the curve at the slider's current value, and a glowing disc recolors to the true emission wavelength via wavelength-to-RGB conversion. Toggling "compare all 3 materials" overlays CdS, ZnS and PbS on the same axes, making it immediately visible why CdS tunes across the visible spectrum, ZnS stays locked deep in the UV, and PbS — with its huge exciton Bohr radius — swings from the infrared all the way into visible light as it shrinks.