Aqueous Phase Synthesized CdSe Nanoparticles with Well-Defined Numbers of Constituent Atoms

Abstract

We report aqueous phase synthesized semiconductor nanoparticles with well-defined numbers of constituent atoms. Aqueous phase synthesis provides many advantages over organic phase synthesis for producing such high-quality semiconductor nanoparticles. We synthesized CdSe nanoparticles with excellent colloidal and optical stabilities directly in aqueous solution at room temperature and then identified them as selectively grown (CdSe)33 and (CdSe)34 magic-sized clusters. These clusters displayed extremely sharp excitonic absorption and emission peaks because of their practically monodispersed size distribution. Their X-ray diffraction pattern and Raman spectral features were considerably different from the corresponding pattern and features for typical crystalline CdSe nanoparticles. Growth of our magic-sized clusters was very slow and proceeded via the formation of different sizes of progressively larger CdSe nanoparticle intermediates with time. Our results demonstrated that aqueous phase synthetic routes could be successfully adopted for producing high-quality semiconductor nanoparticles.

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

“…In our investigation, size focusing and existence of nearly monodispersed, fully grown CdSe nanocrystals also indicates that the formation process did not follow Ostwald ripening growth (i.e., defocusing and broad size distribution), but rather maintained a diffusion-controlled process (size-focusing) 55,57,59 as a form of the livingpolymerzation model.…”

“…After injection of the Se-ODE-HT precursor into the Cd-OLA precursor at room temperature, a broad shoulder was slowly converted into two well-resolved peaks at 335 and 363 nm over the course of 1 h. The shifting of the band-edge absorption peak towards higher wavelength was correlated with the continuous but not the quantized growth model, as reported in the literature. 12,29,57 The position of the lowest energy absorption peak at ~360 nm suggests that our sample may contain MSNs of (CdSe) 19. 58 The peak position at 363 nm and intensity were stable for days at room temperature.…”

Phonon Spectra of Small Colloidal II-VI Semiconductor Nanocrystals

“…Simple estimation shows that at d as small as 1.8 nm, most of the atoms can be classified as surface ones and such NCs can therefore be an illustration of a limiting case of small NC which do not support the bulk-like LO (and TO) phonon modes. Their spectrum more likely resembles the phonon density of states (DOS) predicted for bulk CdSe and CdSe nanowires with a diameter of d = 2 nm [41] or the spectrum of molecular-like clusters [16,42]. From the viewpoint of the model based on bulk dispersion curves, the strong spatial confinement along with lattice distortion due to the reconstruction induced by a domination of surface atoms can lead to the situation when only phonons (TO and LO) close to (bulk) zone boundary exist in NCs.…”

“…Though a number of in-depth studies have addressed the phonon spectra of colloidal [14][15][16][17][18][19][20], glass-embedded [21][22][23] NCs, and epitaxial nanostructures [24][25][26], a significant divergence of the results exists concerning both the nature of the modes and their response to such factors as size, surface conditions, properties of the hosting medium and so forth. In particular, the apparently similar Raman spectra of a wide range of compounds (e.g., II-VI, III-V, and IV) and NC morphologies (dots, rods, tetrapods, wires, and discs) have been assigned differently.…”

Förster Resonance Energy Transfer Mediated Photoluminescence Quenching in Stoichiometrically Assembled CdSe/ZnS Quantum Dot-Peptide Labeled Black Hole Quencher Conjugates for Matrix Metalloproteinase-2 Sensing

“…[1][2][3][4] They are bright emitters and can feature narrow emission ranges that are freely tunable across the whole visible spectrum and having long lifetime of the excited states. [5][6][7][8][9][10][11] Moreover, they are widely available, can be made live-cell compatible by organic coatings and standard coupling chemistry, and aside from transitions to metastable dark states, that is fluorescence intermittency or blinking with power-law statistics, they are exceptionally photostable. This means that they can be transferred many times between their ground ("off ") and their fluorescent ("on") state.…”