Black Embers.

With a twist of your hand, a black orb flickering like an ember forms in your palm. You can cause this orb to detonate as an action as long as you are on the same plane as the black orb. the orb has an AC of 18 and 1 hit point, when this orb is destroyed, dropped from a distance, or used as part of an attack, it detonates.  Upon detonation, each creature within a 5ft sphere centered on the orb must make a Dexterity saving throw as the area is filled with dark embers. A target takes 2d4 fire damage & 2d4 thunder damage on a failed save, or half as much on a success.  

At higher levels. When cast at 2nd level or higher, the damage increases by  4d4 per spell level above 1st level.