Abstract
We report the exotic photoluminescence (PL) behaviour of 3D topological insulator Bi2Te3 single crystals grown by customized self-flux method and mechanically exfoliated few layers (18 ± 2 nm)/thin flakes obtained by standard scotch tape method from as grown Bi2Te3 crystals. The experimental PL studies on bulk single crystal and mechanically exfoliated few layers of Bi2Te3 evidenced a broad red emission in the visible region from 600–690 nm upon 375 nm excitation wavelength corresponding to optical band gap of 2 eV. These findings are in good agreement with our theoretical results obtained using the ab initio density functional theory framework. Interestingly, the observed optical band gap is several times larger than the known electronic band gap of ~0.15 eV. The experimentally observed 2 eV optical band gap in the visible region for bulk as well as for mechanically exfoliated few layers Bi2Te3 single crystals clearly rules out the quantum confinement effects in the investigated samples which are well known in the 2D systems like MoS2,WS2, WSe2, and MoSe2 for 1–3 layers.
Highlights
Topological insulators (TIs) have gained a huge attention among condensed matter physicists credited to their striking multifunctional properties[1,2]
Previous studies on 3D topological insulators (TIs) showed existence of dual band gaps; 0.3 eV corresponding to electronic band gap and 2.1 to 2.3 eV corresponding to optical band gap for the case of CVD grown Bi2Se3 nanoplatelets[14]
It is well-known that Bi2Te3 has a layered crystal structure which consists of five atomic layers blocks, known as quintuple layer (QL)[16]
Summary
Topological insulators (TIs) have gained a huge attention among condensed matter physicists credited to their striking multifunctional properties[1,2]. The most famous examples of 3D TIs are Bi2Te3, Bi2Se3 and Sb2Te3 These materials act as prototypical TIs because of their large intrinsic electronic band gap with a single Dirac-cone-like topologically protected metallic surface state inside the bulk energy gap. Bi2Te3, Bi2Se3 as well as two dimensional (2D) layered materials (MoS2, MoSe2 etc.) could be the potential material for optical applications[12,13,14,15]. Motivated by the interesting quantum properties of 3D TIs, in the present work, we focus on the photoluminescence (PL) studies of both bulk and mechanically exfoliated few layers of 3D TI Bi2Te3 single crystal. Our results show that Bi2Te3 as well other related TIs can act as ideal model systems for generation optoelectronic device applications
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