Blue emission of Sr2−xCaxP2O7:Eu2+ for near UV excitation

Sr2−xCaxP2O7:Eu2+ (x = 0 − 2) phosphors with intense and adjustable blue emission are prepared by solid state reaction. The crystal phase evolution and correlated photoluminescence properties are studied as a function of Ca2+ content based on the experimental measurements of X-ray diffraction, photoluminescence and fluorescence decay. Our results indicate that Sr2−xCaxP2O7:Eu2+ crystallize in single α-Sr2P2O7 type phase for x ≤ 0.75. As increasing x from 0.75, α-Ca2P2O7 type phase starts to form and increase followed by reduction of α-Sr2P2O7 type phase. The single α-Ca2P2O7 type phase is obtained only at x = 2. The emission band (band I) in α-Sr2P2O7 type phase and that (band II) in α-Ca2P2O7 type phase both shift to the red on increasing x due to enhancement of crystal field strength in case of Ca2+ substitution for Sr2+. This substitution also leads to remarkably inhomogeneous broadening of band I, within which energy transfer from the high energy Eu2+ to the low energy one is observed. The superposition of band I and band II results in various distributions of intense emission band including the redshifted and more broadened ones suitable for white light generation.