Low-temperature synthesis and photoluminescence of IIA-VIB nano-phosphors doped with rare earth ions

Eu²⁺ doped CaS nanoparticles were prepared by two kinds of methods, alkoxide and co-precipitation. The as-prepared samples did not show any emission, while the heated samples showed the red emission corresponding to the 4f⁶5d¹ → 4f⁷ transition of Eu ²⁺. No signal of Eu²⁺ was observed in the electron paramagnetic resonance spectra of the as-prepared samples, while the heated samples showed two sets of sextet hyperfine lines corresponding to two isotopes of Eu²⁺ with the mass numbers of 151 and 153. Accordingly, these results indicate that Eu²⁺ ions were incorporated into CaS during subsequent heating to show the red emission.