Ultrospec 4300 pro uv visible spectrophotometer

The water-soluble CdTe QDs were synthesized according to a previously reported method.^{31 (link)} In brief, a freshly prepared NaHTe solution was mixed with a nitrogen-saturated Cd(NO₃)₂ solution at pH 11.2 (adjusted by dropwise addition of 1 M NaOH) in the presence of MPA as a stabilizing agent; the final concentrations of NaHTe, Cd(NO₃)₂, and MPA were 0.76, 1.74, and 2.55 mg mL⁻¹, respectively. The CdTe precursor solution was heated in a water bath at 95 °C. Finally, the resulting CdTe QD solution was stored at 4 °C for future use. The photoluminescence spectrum of the CdTe QDs was recorded by using a fluorescence spectrophotometer (Hitachi F-4500, Tokyo, Japan), and the UV-vis absorption spectra of the CdTe QDs were obtained with an Amersham Pharmacia Ultrospec 4300 pro UV/visible spectrophotometer (England, UK). The size distribution and morphology of the prepared CdTe QDs were characterized by using a high-resolution transmission electron microscope (TEM, JEOL JEM 2100; Tokyo, Japan). The average hydrodynamic diameter and zeta-potential of the resulting CdTe QDs were determined with a particle size analyzer (Zeta Sizer Nano ZS90, Malvern Instruments Ltd, Worcestershire, UK). The fluorescence quantum yield (QY) of the synthetic CdTe QDs was determined using rhodamine 6G as a reference standard (QY = 95%) according to a previously described method.^{43 ,44}