The phrase "atmosphere settled" is correct and usable in written English.
It can be used to describe a situation where the mood or environment has become calm or stable after a period of tension or disturbance.
Example: "After the heated debate, the atmosphere settled, allowing for a more productive discussion."
Alternatives: "mood calmed" or "environment stabilized".
An uneasy atmosphere settled over Rio.
A surreal, pregnant atmosphere settled over politics this weekend.
That missed eagle putt seemed to check Woods' progress a moment and for a while the atmosphere settled back down.
A swathe of warm air in the atmosphere settled over the Chinese capital like a duvet and trapped beneath it pollution from the region's 200 coal-fired power plants and 5m cars.
While people are staying vigilant, when 10pm rolled around with no violence, a party-like atmosphere settled over my neighborhood.
With larger companies decamping and a sour atmosphere settling around Polish shale, independent firms are having a difficult time raising the funds needed to continue prospecting.
"All" includes a torrid affair between the mistress of the house and her husband's business associate; when they're discovered, a stormy atmosphere settles over the household – and that's just the start.
Darkness takes the edge off the tropical heat, and a heady, luscious tropical atmosphere settles over the place.
It is almost impossible to exaggerate the intensity of the fake atmosphere which settled round the young Sovereign.
In the respectable atmosphere that settled like a cloud during the Napoleonic wars, such scenes disconcerted his readers: an article appeared suggesting "that the fair sex, pass overleef on seeing them".
Fly ash, the particulate matter resulting from high temperature combustion of coal, was historically dispersed into the atmosphere and settled as fly-ash spheres on the surface soil from a variety of boilers, including those of steam locomotives and steam-powered farm machinery.
