from Latin splendescent-, splendescens, pres. pple. of splendescĕre to become bright
1848 - Bothie of Tober-na-Vuolich, Arthur H. Clough;
"Splendescent as a god of Olympus."
(as per E-NED and the Historical Thesaurus of English)
earlier example (1795) shown below
From: The Inantity and Mischief of Vulgar Superstitions,
By M.J. Naylor, 1795