Multicolor emission leading by energy transfer between Dy3+ and Eu3+ in wolframite InNbTiO6

Abstract

Exploring new color-tunable phosphors is of significance for light-emitting applications. In this work, multicolor-emitting InNbTiO6:Dy3+,Eu3+ phosphors were formulated and synthesized using the classic solid-state reaction technique. Phase identification indicates the pure wolframite crystal structure of as-prepared samples. According to the Rietveld refinement, dopants have been confirmed to occupy the In3+ site in the InNbTiO6 matrix. The phosphors exhibit strong absorption around 385 and 394 nm, due to the dominated transitions of 4F9/2->6H13/2 in Dy3+ and 5D0->7F2 in Eu3+, respectively, well matching the emissions from the commercial UV LED chips. In single doped phosphors, activators Dy3+ and Eu3+ under the UV light excitation respectively present their unique emission lines. As for the codoped phosphors, the co-activation and sensitization between Dy3+ and Eu3+ have been elucidated under a 394 nm excitation. The addition of Eu3+ into InNbTiO6:0.06Dy phosphor leads to the emission tuning from grass-green to orange-red crossing the warm-white region. The energy transfer can be proved through analyzing the PLE and PL profiles of the co-activated phosphors and evaluating the decay process for Dy3+ ions. According to the Dexter's theory and Reisfield's approximation, the mechanism of coupling effect has been identified to be the electric d-d (dipole-dipole) interaction. When the sum of dopants concentration equals to 0.09, the energy transfer efficiency reaches the maximum value 40.5. Moreover, the thermal stability of a representative InNbTiO6:0.06Dy3+,0.015Eu3+ phosphor have been investigated, which presented and a emission intensity maintenance of 42% at 423 K relative to room temperature 298 K. Besides, the quantum yields of InNbTiO6:0.06Dy3+, 0.04Eu3+ within the luminescence range 603–620 nm are measured to be 33.4% under the ultraviolet radiation of 394 nm. These results demonstrate that these new type phosphors have promising applications in UV LED based white light-emitting devices.