Design, synthesis, crystal structure and luminescent properties of a new tantalum-phosphate KBiTaPO with negligible concentration quenching and good thermostability

The luminous efficiency of rare-earth (Ln)-doped luminescent materials suffers greatly from the negative concentration quenching effect, which can be surmounted by a large separation of Ln ions in the host lattice. Herein, this study reports a novel tantalum-phosphate KBiTaPO (KBTP) that possesses a 'chain-like' structure when viewed along the c-axis, containing [TaO(PO)], K and [Bi(PO)] chains. UV-Vis spectroscopy and density functional theory (DFT) calculations reveal that KBiTaPO has an indirect band-gap of 3.99 eV, making it suitable as a luminescent host matrix. A series of Eu or Tb phosphors KBTP:xEu/Tb (x = 0.1-1) were prepared and their fluorescent performance was studied. Due to the Bi ions being far apart in the KBTP host, the negative concentration quenching effect of the prepared phosphors was greatly limited, even when the concentration of Eu/Tb reached up to 80% replacing Bi. Moreover, both phosphors had good heat-resistance properties at 30-200 °C, keeping 85.6% (KBTP:0.8Eu) and 71.3% (KBTP:0.8Tb) of the initial intensity at 200 °C. These results preliminarily suggest that KBTP is promising as a host material for both Eu and Tb fluorescence.