lustre of gems, glitter, shine
璀 centers on the bright, reflective quality of gems: their lustre, glitter, and shine.
璀 combines 王 (jade/gem) with 崔, which likely contributes the sound. The character expresses the lustre or glitter of gems.
The left side 王 represents a gem or jade. Picture a gemstone sparkling so brightly that its shine is almost blinding—that is the lustre of 璀.
For サイ, imagine a gem so brilliant it makes you sigh in admiration: sigh -> サイ, as you gaze at its glittering surface.
—