A series of novel Ce3+ singly doped and Ce3+/Mn2+ co-doped color-tunable KBaY(BO3)2 phosphors were synthesized by a high-temperature solid-state reaction, and the crystal structures and luminescence properties were investigated in detail. The crystallographic cation sites occupancy of the doping Ce3+ and Mn2+ ions for KBaY(BO3)2: Ce3+, Mn2+ samples were analyzed by the Rietveld refinement method. It was demonstrated that Ce3+ and Mn2+ ions can both enter into the two types of cation sites in the KBaY(BO3)2 crystal lattice, with a slight tendency of occupancy for Ce3+ on Y3+ ion sites and Mn2+ on the Ba2+/K+ ion sites. By controlling Mn2+ ions content with a fixed Ce3+ concentration, the emission color of the phosphor varied from blue (0.160, 0.150) to pink-white (0.348, 0.272) and eventually to orange (0.490, 0.372). The critical energy transfer distance calculated by the concentration quenching theory was 16.52 Å and the energy transfer from Ce3+ to Mn2+ took place via a resonance-type dipole–dipole mechanism. By combining the single-phase KBa0.97Y0.97(BO3)2: 0.01Ce3+, 0.05Mn2+ phosphor with an n-UV 370 nm InGaN chip, a phosphor-converted white LED lamp was successfully fabricated, producing a white light with a warm correlated color temperature of 4710 K and color coordinates of (0.347, 0.307).

•Novel rare-earth borate KBaTbB2O6 was synthesized using a conventional solid-state reaction method.•The crystal structure of KBaTbB2O6 has been determined by the Rietveld analysis.•Tunable emission in red wavelength range was realized by controlling Eu3+ ions content.Novel rare-earth borate KBaTbB2O6 was synthesized using a conventional solid-state reaction method. The crystal structure of KBaTbB2O6 has been determined by the Rietveld analysis, which demonstrates that the final chemical composition is K0.46Ba0.54Tb0.49BO3 and KBaTbB2O6 is isomorphous with KBaY(BO3)2 and crystallizes in the planar trigonal [BO3]3− group R-3 m with lattice parameters of a=5.4562(4) Å, c=17.8629(2) Å, and Z=3. Tunable emission in red wavelength range was realized by doping and controlling Eu3+ ions content into KBaTbB2O6. The critical energy transfer distance calculated by the concentration quenching theory was 6.64 Å and the energy transfer from Tb3+ to Eu3+ took place via a resonance-type mechanism.