Morphology control and luminescent properties of Eu/Tb-doped calcium carbonate nanoparticles using natural limestone

The Eu/Tb-doped CaCO3 nanocrystals including nanoneedles, nanorods and nanospheres are respectively synthesized from natural limestone via carbonation technique. The doping of Eu/Tb ions can not change the polymorph, but the morphologies and sizes of synthesized CaCO3 differ significantly depending on the species and concentrations of Eu/Tb ions. The undoped CaCO3 nanoneedles exhibit a length of 280–920 nm and a diameter of 55–78 nm, while the 6% Eu doped CaCO3 nanorods exhibit a length of 1.68–2.56 μm and a diameter of 560–680 nm, respectively. The introduction of Tb ions changes the CaCO3 morphology from nanoneedle to irregular sphere and the diameter of CaCO3: 8% Tb primary particle is around 110–200 nm. Under the excitation of 318 nm or 384 nm ultraviolet light, CaCO3: x% Eu nanorods exhibit characteristic emission bands at 360 nm and 420 nm assigned to 4f6 5 d1(t2g) →8S7/2 transition of Eu2+ ions and sharp peaks at 596 nm from the 5D0 →7F1 transitions of Eu3+ ions. XPS data further confirm the coexistence of Eu2+ and Eu3+ ions. The CaCO3: y% Tb nanospheres present intense blue-green emission at 424 nm and 545 nm under excitation at 397 nm, which are originating from both 5D3→7FJ and 5D4→7FJ transitions of Tb3+ ions. However, under 343 nm excitation, in addition to the emission of Tb3+, Eu3+ ions also present intense emissions at 572 nm, 596 nm, 624 nm and 650 nm, which may be caused by the unknown Eu -containing impurities from natural limestone. Whiteemitting and color-tunable photoluminescence performance of CaCO3 nanostructures are realized by regulating the excitation wavelengths and doping ions. •Calcium carbonate with different morphologies were synthesised from natural limestone.•The microstructure and photoluminescence of Eu/Tb-doped CaCO3 were studied.•Eu- doped CaCO3 nanorods exhibit characteristic emission of both Eu2+ and Eu3+ ions.•Tb-doped CaCO3 nanospheres exhibit multicolor luminescence from both Eu3+ and Tb3+ ions.