Colloidal quantum dots (CQDs) implementation in optoelectronics is limited by internal material imperfections such as a fluorescence intermittencies (blinking) and its spectral stability (spectral diffusion). Both the effects originate in the material ability of extra energy exclusion from the system and closely packed charges. A turning point occurred when a few distinctive systems with blinking free behavior were reported in CQDs with either type – I, type – II or quasi – type – II core/shell configurations2. The particular interest gains the “giant” CQDs with quasi – type – II configuration such as CdSe/CdS3. This “giant” particle size enables to decrease the charged carriers interaction. The later results in reduction of the non – radiative Auger and paves the way for non – blinking material. However, the increase of the particles size above bulk exciton Borh radius decries the strength of quantum confinement.In this work we explore the effect of weak and extremely weak quantum confinement on exciton (X) and bi-exciton (BX) fine structure in CdTe/CdSe “giant” CQDs. The particles under consideration were covered with two monolayers of CdSe on top of CdTe core with total particle diameter of 9.5 nm (Sample A) and 25.5 nm (Sample B).The major difference between two samples lies in CdTe core size which is less than its bulk exciton Borh radius (7.3 nm) in sample A and significantly excides it in sample B.Both of the samples possess an efficient BX formation along with almost complete suppression of X emission line (BX formation due to substantial filling2). In extremely weak confinement regime (sample B) X and BX do not exhibit any well resolved polarization dependent fine structure leaving only slight elliptical cross polarization of both the emission bands. The exchange interaction induced excitonic fine structure was not resolved even with increase of external magnetic field strength leading only to overall emission line broadening due to Zeemann of the sub bands. On the other hand, the weak confinement regime (sample A) both of the bands possesses well resolved cross polarized emission lines from their energy fine structure already at zero Tesla magnetic field strength. This was further splitted at higher magnetic field powers.

References:

1              in preparation

2              Osovsky et al., Phys. Rev. Lett. 102, 197401 (2009)

3              Chen et al., J. Am. Chem. Soc., 130, 5026 (2008)