The Halcyon Company was created in 2007.

Halcyon House was created in 1787.

Halcyon - console - was created in 1985.

"Halcyon days" denotes a period of time, not really a sense. So you could say, 'those halcyon days when i spoke to you'.

'Halcyon' as an adjective, means peaceful, calm, happy and carefree, after the halcyon, or kingfisher, which was believed to make its nest/lay its eggs out at sea.

You could perhaps say 'I felt a halcyon sense after talking to you.', but 'halcyon, other than in the set phrase 'halcyon days' sounds a bit pretentious.

Ah, how we reveled in those halcyon days!