Demonstration of Bulk Semiconductor Optical Properties in Processable Ag₂S and EuS Nanocrystalline Systems

Abstract

Semiconductor nanocrystals (NCs) are colloidal single crystals that have been widely examined in recent years to elucidate the origins and applications of size-tunable properties. Size-tunable optical properties are particularly desirable for applications in light-emitting devices, lasers, and biological labeling. [1][2][3][4][5] Strong confinement effects, characteristic of many NCs (''quantum dots''), give them an electronic structure more like molecules than semiconductors and this is of special interest in areas such as quantum information.[6] However, while all colloidal quantum dots are NCs, not all NCs are colloidal quantum dots. This distinction between bulk and confined nanocrystals is not always obvious depending on the characteristics of the bulk band structure. In this paper we show that the optical spectra of bulk semiconductor NCs can exhibit surprising features that may be confused with quantum confinement effects. We compare the optical properties of two bulk nanocrystal systems, Ag 2 S and EuS.Bulk semiconductors have revolutionized a breadth of technologies as a consequence of the way electronic levels form delocalized bands. Although the development of new quantum dot systems have dominated semiconductor nanocrystal research, we suggest that the field of bulk NC synthesis and characterization is complementary to the well-established field of quantum-confined NCs, and offers great potential for the discovery of materials that exploit the desirable electronic and magnetic attributes of bulk semiconductors on the nanoscale. A key advantage foreseen for these NCs is that they are easily processed and they can potentially be programmed for intelligent self-assembly. [7] The realization of the scope and potential of nanoscience has stimulated the discovery of many routes for semiconductor quantum dot synthesis. Many of these reports seek to demonstrate quantum-confinement effects; that is, size-tunable absorption features as demonstrated in compelling pioneering work. [8,9] Compared to the extensive amount of research directed towards creating novel quantum dot systems, little work has been directed towards thinking about the potential of colloidal synthesis for the miniaturization of semiconductors while retaining the essential attributes of the bulk material. There are some notable exceptions to this including nanocrystalline TiO 2 which has been extensively studied for use in photovoltaics.[10] Bulk semiconductors have been, and continue to be, essential components in almost all aspects of technology. They differ from quantum-confined semiconductors in that carriers are located in bands rather than discrete energy levels, thus producing the well-known electronic properties. Nanocrystals that have these same properties could potentially find wide application in micro-and nanoelectronics because they may facilitate processing of devices on small length scales without introducing complicating quantum effects. These materials would exploit the advantages of nanocrystals, such as enhanced processabilit...

Control Over the Crystallinity and Defect Chemistry of YVO4 Nanocrystals for Optimum Photocatalytic Property

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Controlling the Optical Properties of Inorganic Nanoparticles

“…As we reported recently, such a semiconductor material is EuS, which should exhibit bulk behavior on the nanoscale according to the estimated electron and the hole Bohr radii, which are less than 1 nm. [62] Nanocrystalline EuS has been the subject of ongoing experimental and theoretical investigation because of its interesting magnetic properties. [63][64][65] EuS exhibits ferromagnetic behavior with a Curie temperature of 16 K and is a candidate model system for demonstrating spintronics or optoelectronic phenomena.…”

“…[63] In fact, it is a band characteristic of bulk EuS originating from electron excitation from localized Eu 2þ 4f 7 orbitals to the lower 5d conduction sub-band (the conduction band is split into this lower and an upper sub-band by the crystal field splitting of 2.1 eV). [62] This is an example of how a feature-rich bulk band structure can contribute bands to the optical absorption of nanocrystals. Adopting such a strategy in conjunction with confinement effects might have interesting consequences.…”

A Simple Reducing Approach Using Amine To Give Dual Functional EuSe Nanocrystals and Morphological Tuning

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