Photoluminescent blue-shift of organic molecules in nanometre pores

Porous alumina was fabricated by anodization in sulfuric acid and oxalic acid, where a laser dye, rhodamine 6G (RG6), and another luminescent organic molecule 8-hydroxyquinoline aluminum (Alq₃) were impregnated. The morphology determined by atomic force microscopy shows that the size of the pores is about 10-15 nm for alumina prepared in sulfuric acid (H₂SO₄) and about 40-50 nm in oxalic acid (H₂C₂O₄). An obvious blue-shifted photoluminescence (PL) of Alq₃ and RG6 in nanometre-sized holes was observed. The measured spectral characteristics demonstrate the influence of the pore size on the emission of the organic molecules. The PL blue-shift of the molecules in smaller nanometre-sized holes is larger than that in larger holes.