Substance inside early flat-screen TVs

PLASMA

This ionized gas glows when electrically charged and was also studied in physics for its unique state between solid and liquid.

Early flat-screen TVs often used plasma display technology, where tiny cells of ionized gas (plasma) lit up to create images. The clue points directly to this substance—plasma—as the key material inside those screens. No wordplay here, just a straightforward reference to the tech behind older TV models.