In the present work related to the development of high-luminous blue-emitting calcium aluminate phosphor, the active role of boric acid (H3BO3) as a chemical additive is identified. The appropriate usage of H3BO3 in defining the crystal structure, morphology and momentous variation in luminescent properties of calcium aluminate long persisting (LP) phosphor is systematically studied and presented. The results attribute two major roles for H3BO3; as a flux for promoting the formation of required crystalline phase, when added in the amounts less than 10 mol% and as one of the precursors for the formation of aluminoborate complex when added above 10 mol%. This amount could be treated as a threshold for aluminoborate complex formation. Luminescent studies revealed that out of all phases identified, CaAl2O4 is the only phase contributing for maximum photoluminescence (PL) augmentation and long persistence (10-12 h) from Eu2+ and Nd3+ ions, respectively. The relevant chemistry and reaction mechanism involved during solid-state synthesis of rare-earth doped calcium aluminate LP phosphor system have been discussed with greater emphasis on the luminescent properties affected with the addition of boric acid. (c) 2006 Elsevier B.V. All rights reserved.