fig11

Figure 11. (A) Crystal structure of [Yb₂Er]⁺ and the positive mode of ESI-MS spectra of [Yb₂Er]⁺/[Er₂Yb]⁺ in MeOH; (B) DL spectra (λ_ex = 980 and 400 nm) of [Yb₂Er]⁺ before and after addition of 2 equiv of fluoride in solid state; (C) The fluoride-dependent UCL of [Yb₂Er]⁺ (2 × 10^-4 M) under 2 W/cm² in CH₂Cl₂; (D) The P-dependent UCL of [Yb₂Er]⁺ (2 × 10^-4 M) with 3.5 molar equivalent [Bu₄N]F. This figure is used with permission from Wiley-VCH GmbH^[45]. UCL: Upconversion luminescence; ESI-MS: electrospray ion mass spectra; DL: downshifting luminescence.