Blasting Smite

The next time you hit a creature with a weapon attack before this spell ends, the weapon crackles with fiery energy. The attack deals an extra 1d6 fire damage to the target and then a 15ft cone of fire damage erupts from the blade, all creatures in the cone, including the one you struck, must make a dexterity saving throw. On a failure a creature takes 2d4 fire damage, on a success the creature takes half damage. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage of the cone increases by 1d4 for each slot level above 2nd.