Near-field Energy Transfer and Color Conversion from an InGaN/GaN Quantum-well Structure into Inserted Colloidal Quantum Dots in a Metal Nanotube

A series of Ag nanotube (NT) sample with different Ag deposition thicknesses on an InGaN/GaN quantum-well (QW) structure are fabricated by using the technique of secondary sputtering for forming the Ag sidewall in a GaN surface nanohole (NH). After the insertion of the photoresist solutions of colloidal quantum dots (QDs) into the metal NTs, the efficiencies of the Förster resonance energy transfer (FRET) from QW into QD in those samples are evaluated through time-resolved photoluminescence measurement. The FRET efficiencies of the metal NT samples are higher than those with QDs on the top surface or inserted into GaN NHs (no Ag deposition). Among the metal NT samples under study, the FRET efficiency reaches a maximum when the Ag deposition thickness is ~ 36 nm. The enhancement of the FRET efficiency in a metal NT sample is mainly attributed to the higher dielectric-constant contrast between the metal NT sidewall and the medium inside the NT, leading to a stronger nanoscale-cavity effect. Based on continuous photoluminescence measurement, the similar enhancement behavior of color conversion can also be observed. A simulation study is undertaken to confirm the enhanced FRET and color conversion in a metal NT.