Selenium is why ZnSe works in the infrared and why the Gwangju site has a gas plant, not just a saw. H2Se is not a romance. It is the reagent.
Elemental selenium is a group-16 solid — grey hexagonal, red amorphous, the usual allotrope circus. In ZnSe it occupies the anion site. The Se 4p states dominate the valence band; that chemistry is what pushes the reststrahlen and the IR window out where CO2 and LWIR cameras live. No selenium, no 10.6 µm optic. Also: no selenium, no special toxicity file.
Hydrogen selenide
The CVD reaction we run is, in one line:
Zn (g) + H2Se (g) → ZnSe (s) + H2 (g)
H2Se is a colorless hydride with a rotten, garlic-radish smell at concentrations you should never be standing in. It is toxic at low ppm, flammable, and heavier than air. The factory photograph of the H2Se gas facility is not décor. It is the reason this is a chemical process plant adjacent to an optics plant. You do not “order selenium powder and melt a window.” You generate or receive hydride, meter it, scrub the effluent, and treat the operators as if a leak is a real event — because it is.
What that means on your dock
The finished window on your receiving bench is not H2Se. It is a solid II–VI. It is still classified as a hazardous optical material: dust from grinding, fumes from a fire, acid-soluble selenium compounds. SDS is not optional. We will send the KM Innovation zinc selenide SDS with the quote. Do not dry-grind this crystal in an open shop and call it a Tuesday.
If your EHS group asks “where does the selenium come from,” the honest answer is: from a hydride CVD in Gwangju, not from a melt in Florida. The Florida desk quotes, stocks and ships. The chemistry stays in Korea.