Color tuning of the Ba1.96Mg(PO4)2:0.04Eu2+ phosphor induced by the chemical unit co-substitution of the (BO3)3− anion group

Abstract

Replacing the tricolor blend of phosphors by a single-phase white-emitting phosphor has emerged as a new technology for devising white-light-emitting diodes (WLEDs). Modification of the local structure in the crystal plays the key role in obtaining a single-phased, high CRI white-emitting phosphor. This process can also be employed to tune the color emission of the phosphor, especially those doped with Eu2+ ions. In this context, the selection of an appropriate host and the substituting chemical unit plays a vital role, as the crystal environment of the host greatly influences the photoluminescence (PL) emission of the Eu2+ ions. Herein, the color tuning of a new single-phase solid-solution Ba1.96Mg(PO4)2−x(BO3)x:0.04Eu2+ (x = 0.2, 0.5, 0.7, 1, 1.2 and 1.5) phosphor synthesized by the sol-gel/Pechini method is demonstrated. The structural variation induced by the varying composition of the borate (BO3)3− unit was analyzed by X-ray diffraction and Rietveld refinement studies. Fourier transform infrared spectroscopy revealed the presence of the vibrations corresponding to both the BO3 and PO4 chemical groups in the Ba1.96Mg(PO4)2−x(BO3)x:0.04Eu2+ phosphor. Morphological variations were also observed with the chemical co-unit substitution, which was analyzed with Scanning Electron Microscopy (SEM). PL studies indicated that the color tuning from blue-white-orange light, under near UV excitation, was achieved by varying the composition of the (BO3)3− group. The co-existence of the PO4 and BO3 groups gave rise to a higher-energy emission (420 nm) and a lower-energy emission (585 nm), respectively. The PL decay curves were analyzed to estimate the energy transfer efficiency between the higher-energy and lower-energy emission sites of the phosphor. This work presents a new strategy to tune the color emission of a singly-doped phosphor by modifying the structure of the host lattice.