Size quantization effect in highly stable UV emitting HgTe nanoparticles: Structure and optical properties

Abstract

We report a simple one pot aqueous chemical synthesis route to fabricate very small and highly stable HgTe nanoparticles ͑NPs͒ capped with L-cysteine ethyl ester hydrochloride ͑LEEH͒. The LEEH concentration has found to be critical for desired size NP synthesis. Structural analyses by grazing angle x-ray diffraction and high resolution electron microscopy studies indicate HgTe NPs to exhibit a fcc phase with ͗111͘ prominent reflection having monodispersed NP size of around 2.0 nm. A strong size quantization effect marked by a prominent excitonic absorption at 4.436 eV blueshifted by 4.586 eV from the bulk band gap value has been observed in their optical absorption studies. A strong and narrow Gaussian fluorescence emission at 3.3 eV has been observed for 2.0 nm NP size whose width is being narrowed down with increasing LEEH concentration. The strong UV range absorption and emission have been observed for the first time in HgTe NPs.

Epitaxial growth of colloidal hydrophilic lattice matched HgTe/CdTe core/shell nanocrystals for UV luminescence

“…The NP sizes of the core and core/ shell are estimated from the full width at half maxima (FWHM) of the intense <111> diffraction peak according to Scherer equation and are presented in Table 1 along with HRTEM data for comparison. The narrow Bragg peaks obtained from GXRD measurement is due to narrow size distribution in the nanocrystals even if the particle sizes are small and is in agreement with reference [18]. The sizes estimated from GXRD are little less than those obtained from HRTEM which are in agreement with the reported results of HgTe prepared by hydrophobic capping agents [20].…”

“…The synthesis of HgTe is carried out as follows: 0.32 mM of tellurium powder was reduced by 1 mM sodium borohydride in water which produces NaHTe. To this solution, LEEH capped Hg (0.32 mM) was added and stirred for 4 h at 90 C to form LEEH capped HgTe NPs [18]. Reduction of Te powder and the formation of LEEH capped HgTe NPs are carried out by the following reaction scheme: To avoid oxidation of Te in solution phase, N 2 was bubbled continuously into the solution.…”

“…The equal lattice parameter of HgTe and CdTe is expected to generate lesser strain at the core/shell interface. LEEH capped stable HgTe NPs with narrow size distribution exhibiting strong excitonic absorption and emissions have already been reported [18]. This work is being extended to fabricate a high luminescent and stable lattice matched HgTe/CdTe core/shell NPs.…”

“…4) is ascribed [18] to the excitonic recombination similar to the case of the HgTe (size, 5.0 nm) and HgTe/CdTe core/shell (size, 7.0 nm) (see reference [34]), accompanied with a large non-resonant Stokes shift [41,42] which is inversely proportional to the NP size [43], strain in the NPs, although small (Table 1) and the organic ligand coating [41]. The FL of CS2 appearing at 376 nm due to strong QCE and excitonic recombination red shifted by 77 nm from the excitonic absorption maxima is in contrast to band edge recombination commonly observed in IIeVI core/shell structures such as CdSe/ZnS [18] and CdSe/CdS [2,4]. These core/shells structures of which the cores are in the size range of 2e5 nm whereas the Bohr exciton radii are also in the range of 3e5 nm.…”

New metalorgano-chalcogenide compounds based on polymeric frameworks constructed by Se–Hg intermolecular interactions: Preparation, structural characterization, and Raman evaluation

“…Supramolecular arrangements [2,3], dimeric arrays [4,5], and noteworthy systems exhibiting hypervalent and charge-transfer properties [6,7] have been determined in solid state and are regarded as important structural features of derivatives of organo-chalcogenium halides (Se and Te). Nanosized materials based on II-VI metal chalcogenides are also receiving considerable attention because of their remarkable optical and luminescent properties [8][9][10][11][12][13][14][15] and possible applications to technological devices [16][17][18][19][20]. In this perspective, metalorganic chalcogenide chemistry plays an important role, providing strategies for the preparation of metal-chalcogenide nanoparticles, such as CdTe, HgTe, and ZnTe, from molecules that have structural metal-chalcogen bonds [21][22][23][24].…”