Color tunable and energy transfer mechanism of Dy3+ and Eu3+ rare earth ions activated NaCaBi2(PO4)3 eulytite type phosphor for NUV excitable warm white light emitting diodes

Abstract

The Dy3+ and Eu3+ individually doped and co-doped NaCaBi2-x(PO4)3 (hereafter called as NCBP) eulytite type phosphors were prepared by solid state reaction method with different doping concentrations. The phase formation and the morphological studies were analyzed using the PXRD data and SEM images respectively. The structure of the NCBP host was modeled by VESTA software using the results obtained from the Rietveld refinement analysis. The band gap of the NCBP host and the Dy3+, Eu3+ ions doped /co-doped NCBP phosphors were estimated from the DRS measurements. The luminescence spectra and decay curves of the phosphors were analyzed. The energy transfer mechanism between the Dy3+ and the Eu3+ ions in the NCBP:0.07Dy3+,xEu3+ was investigated. The CIE chromaticity co-ordinates of the NCBP:xDy3+ were located in the cold (5695 K) and neutral white region (4894 K). For NCBP:xEu3+, these co-ordinates lie in the reddish orange region with low CCT values (1622 to 1671 K). By changing the Eu3+ content in the co-doped phosphors and exciting at suitable wavelengths (350, 362 and 395 nm), the emission color could be tuned from neutral white (4661 K) to warm white (2725 K) to reddish orange light (1756 K). These results suggest that the co-doped phosphors might be potential color tunable candidates for the NUV excitable warm WLEDs.