This paper studies potential energy savings that can be realized in dual connectivity heterogeneous networks (HetNets) with densely deployed small cells. Using the Phantom Cell Concept (PCC) as a reference architecture, a novel database-aided mechanism is introduced to provide macro cell-controlled sleep mode functionality to small cells. System level simulations show that a system with this capability can yield energy savings of up to 40% and throughput gains of about 25% in dense deployment scenarios compared to a system where no energy savings scheme is implemented.