Vampiric Smite

The next time you hit a creature with a weapon attack before this spell ends, the weapon is engulfed in grim darkness as you strike. The attack deals an extra 2d6 necrotic damage to the target. Additionally, the target must succeed on a Constitution saving throw or suffer an additional 1d6 necrotic damage and cannot regain hit points until the end of its next turn.  You gain temporary hit points equal to the amount of necrotic damage dealt by this spell. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the extra damage increases by 1d6 for each slot level above 3rd.