Energy Transfer and Avalanche Upconversion of Nd_xY_1-xVO₄ Nanocrystals

We explore Nd³⁺ concentration and excitation power dependences of the avalanche upconversion of Nd_xY_1-xVO₄ (x=0-1) nanocrystals with uniform size and shape. The avalanche threshold power caused by the near-resonant energy transfer between ⁴F_5/2→⁴I_13/2 and ⁴F_5/2→²G_9/2 significantly decreases as the Nd³⁺ concentration increases. The off-resonant energy transfer between ⁴F_5/2→⁴I_13/2 and ⁴F_5/2→⁴G_11/2 in the strong excitation regime leads to apparent broadening on the blue-side of the upconversion spectrum of NdVO₄ nanocrystals.