Krypton is a noble gas with a density of about 3.749 g/L and a melting point around −157 °C, much heavier than air and chemically extremely inert. It has irreplaceable uses in lighting, building energy efficiency, and semiconductor lithography. In lighting, krypton is filled into high-intensity discharge lamps and high-performance incandescent lamps: because of its heavy atoms and low thermal conductivity, higher luminous efficiency is achieved inside a smaller bulb, commonly used for airport runway lights, studio lights, and premium automotive headlamps. In building energy efficiency, krypton is used as the fill gas in insulating glass units; with lower thermal conductivity than air it markedly improves window insulation, and is standard in passive houses and premium curtain walls. In semiconductor manufacturing, the krypton-fluoride excimer laser KrF uses 248-nanometer ultraviolet light, a key light source for large-scale integrated circuit lithography, supporting chip fabrication from micron to deep-submicron nodes. Krypton also serves in particle physics detectors and specialty lamp filling.
Krypton forms very few compounds, and only under extreme conditions. Krypton difluoride KrF2 is one of the few known stable krypton compounds, a colorless solid used as a strong oxidizer and fluorinating agent. The krypton-fluoride excimer KrF is the working medium of lithography lasers, producing 248-nanometer ultraviolet light under discharge and used for chip lithography. Beyond these, krypton forms almost no other stable compounds and is used industrially directly as elemental gas or liquid.
