Fig. 2. (a) PL excitation spectra (dash-dotted line, λ_em = 650 nm), PL emission spectra (solid line, λ_ex = 470 nm), and (b) PL decays (λ_em = 650 nm) of the as-synthesized CaS:0.06%Eu²⁺ and CaS:0.06%Eu²⁺, 0.006%Sm³⁺ NCs. (c) PL emission spectra (λ_ex = 270 nm) and (d) PL decays (λ_em = 400 nm) of the as-synthesized CaS:0.06%Eu²⁺ and CaS:0.06%Eu²⁺, 0.006%Sm³⁺ NCs. The insets in (c) show the corresponding photographs of the NCs under 254 nm UV lamp illumination. IR in (d) represents the instrument response.