Stable Red Emission from Nanosheets of Molecularly Doped Hexagonal Boron Nitride

Abstract

Achieving visible photoluminescence (PL) from hexagonal boron nitride nanosheets (hBN-ns) is synthetically very much challenging due to its intrinsically high electronic band gap. We have explored the concept of molecular doping in turning on PL from hBN-ns in the red region of the visible spectrum. Solution of organic electrophile, tetracyanoquinodimethane (TCNQ), was mixed with the dispersion of exfoliated hBN-ns and molecularly doped hBN nanosheets (md-hBN-ns) were isolated. Detailed mechanistic investigations evidenced the presence of dicyanotoluoylcyanide (DCTC) anion-an oxidative decay product of TCNQ-as the dopant species. Density functional theory calculations revealed a selective and strong bonding scenario between the negatively charged DCTC moiety with the positively charged boron vacancy (V-B) in hBN, giving rise to optically active electronic states within the hBN forbidden gap, which were assigned to be the primary source of such an unusual emission from chemically derived md-hBN-ns.