Figure 6

The UC emission spectra (a), CIE1931 chromaticity diagram (b), and integrated intensities (c) of blue (²H_11/2, ⁴S_3/2 → ⁴I_15/2) and red (⁴F_9/2 → ⁴I_15/2) emission bands of core β-NaYF₄:2%Er³⁺,19%Yb³⁺ nanoparticles upon 976 nm laser diode excitation in range of 0.73 to 9.95 W/cm². The luminescence decay curves of synthesized β-NaYF₄:2%Er³⁺ CNP (d) and β-NaYF₄:2%Er³⁺,19%Yb³⁺ CNP (e) recorded at 520 nm (blue curves), 545 nm (dark cyan curves) and 650 nm (red curves) under 976 nm excitation. The corresponding energy levels diagram of NaYF₄:Er³⁺,Yb³⁺ nanoparticles (f).