A single-phase, thermally stable and color-tunable white light emitting Na2Ca1-x-yCexMnyP2O7 phosphors for white light emitting diodes via energy transfer

The solid-state reaction method was used to develop a series of Na2Ca1-x-yCexMnyP2O7 phosphors in an H2-N2 environment. The crystal structure of the pyrophosphate host, valence state of dopants (Ce, Mn), emission behavior of dopants, energy transfer mechanism, and thermal quenching behavior were thoroughly examined. Doping with Ce3+ and Mn2+ ions enhanced the photoluminescence characteristics of Na2Ca1-x-yCexMnyP2O7 while having negligible effect on the host's phase purity. Under 365 nm UV light irradiation, the addition of Ce3+ ion in the Na2CaP2O7 host revealed an asymmetric band with the typical blue emission around 415 nm and a shoulder around 455 nm. To obtain white light, Mn2+ ion was supplementarily substituted to the present system. When the Mn2+ ions concentration was elevated in the Na2CaP2O7 host, the emission intensity of 560 nm peak corresponding to Mn2+ transition enhanced significantly at the cost of Ce3+ emission of 415 nm. The systematic decrease of Ce3+ emission intensity and corresponding increase in the Mn2+ intensity with the increase in Mn2+ concentration indicated the possibility of effective energy transfer from Ce3+ to Mn2+ ions. The obtained results indicated that energy transfer from the Ce3+ to Mn2+ ions governed by dipole-quadrupole interaction. Because of the efficient energy transfer, the blue emission from Ce3+ and the orange red emission of Mn2+ provide white light from a single host along with high value of activation energy and low thermal quenching behaviour make the present phosphors to be suitable for high-power LEDs.