Ven. Huifeng or Jeff may know.
The source would depend on which is the older sutra between the Avatamsaka & the Original Karmas one. Also, chapters can be and were, stand-alone sutras, so the earliest appearance of these stages is not known by me.
Revealing one essence: this means the inherently pure, complete, luminous essence, which is pure of its own nature. -- Fa-tsang