Opening the book…
Like bipolar transistors, SCRs and TRIACs are also manufactured as light-sensitive devices, the action of impinging light replacing the function of triggering voltage.
Optically-controlled SCRs are often known by the acronym LASCR, or Light Activated SCR. Its symbol, not surprisingly, looks like Figure below.
Light activated SCR
Optically-controlled TRIACs don’t receive the honor of having their own acronym, but instead are humbly known as opto-TRIACs. Their schematic symbol is shown in Figure below.

Opto-TRIAC
Optothyristors (a general term for either the LASCR or the opto-TRIAC) are commonly found inside sealed “optoisolator” modules.
This page titled 7.7: Optothyristors was last modified on Sat, 20 Mar 2021 03:12:35 GMT and is shared under a GNU Free Documentation License 1.3 license and was authored, remixed, and/or curated by Tony R. Kuphaldt (All About Circuits) via source content that was edited to the style and standards of the LibreTexts platform.
The book could not be loaded just now.