Upconversion Emission Modification and White Light Generation in NaYF 4 :Yb 3+ , Er 3+ , Tm 3+ Nanocrystals/Opal Photonic Crystal Composites

In this paper, we fabricated NaYF 4 :Yb 3+ , Er 3+ , Tm 3+ nanocrystal/opal photonic crystal composites by depositing NaYF 4 :Yb 3+ , Er 3+ , Tm 3+ nanocrystals on the surface of opal photonic crystals, and we investigated the influence of photonic bandgaps on upconversion (UC) emission properties of NaYF 4 :Yb 3+ , Er 3+ , Tm 3+ nanocrystals. When the photonic bandgaps overlapped with the UC emission bands of NaYF 4 :Yb 3+ , Er 3+ , Tm 3+ nanocrystals on the opal photonic crystal surfaces, the suppression or enhancement of UC emissions was observed due to the Bragg reflection effect of photonic crystal, resulting in the modification of red, green, and blue UC emissions. Thus, white UC emission was realized.