A series of (Ca2-x/2-yEuy square(x/2))(Si1-xPx)O-4 (0 <= x <= 0.20 and 0.02 <= y <= 0.05) green-emitting phosphors were synthesized, and characterized by photoluminescence (PL) spectroscopy and X-ray powder diffraction. We compared the PL intensities between the phosphors that were annealed at 1373-1773 K and those of non-annealed ones. Actually, the (Ca1.95Eu0.02 square(0.03))(Si0.94P0.06)O-4 phosphor, when annealed at 1473 K for 4 h, exhibited the highest PL intensity, which was 1.6 times higher than that of the non annealed (Ca1.96Eu0.02 square(0.03))(Si0.96P0.04)O-4 phosphor. The coexistence of the alpha'(L)- and beta-phases would be essentially important for the enhancement of PL intensity and eventually provide a favorable environment for the efficient PL emission of Eu2+ ion. The disc-shaped sintered phosphor that was annealed at 1773 K clearly showed the core-shell structure, consisting of the red-emitting phosphor core and the green-emitting phosphor as shell. This unique structure in the annealed phosphor would be formed during the phase transitions. (C) 2016 Elsevier Ltd. All rights reserved.