Method A. Five grams of dodecylamin

Method A. Five grams of dodecylamine (DDA) were
dissolved in 7 mL of tri-n-octylphosphine (TOP) at 50 °C in a
50 mL two-neck flask with a reflux condenser attached. Subsequently,
0.11 mL (1.47 mmol) of dimethylcadmium and
0.128 g (1 mmol) of tellurium powder were added under stirring,
and the temperature was slowly increased to 180 °C. After 30
min, the temperature was raised to 200 °C, and growth of the
nanocrystals was allowed to proceed at this temperature for
20 h. Under these conditions, tellurium slowly dissolves in the
reaction mixture, resulting in a very slow growth of CdTe
nanocrystals at sufficiently high temperatures. Finally, toluene
was added to the warm solution, and the mixture was left for
24 h at room temperature under stirring.
This method allowed obtaining CdTe nanocrystals in the size
range of 4.0-6.0 nm, emitting from yellow to red with
extremely high PL quantum yields exceeding 60%.
Method B. A 0.65 g sample of tellurium was dissolved in
10 mL of TOP by overnight heating at 220 °C. After cooling
to room temperature, 1.96 mL of the resulting greenish-yellow
solution was mixed with 0.11 mL (1.47 mmol) of dimethylcadmium
and 3 mL of TOP. This mixture was loaded into a
5 mL syringe and injected into 10 g of DDA vigorously stirred
at 150 °C in a 50 mL two-neck flask with attached reflux
condenser. Directly before injection, the heater from the reaction
flask was removed. The deep-yellow transparent solution
obtained after injection slowly changed its color to bloody-red
with time. Heating was resumed after approximately 10-15 min
when the temperature of the reaction mixture had reached 90-
100 °C. This initiated further slow growth of the particles, which
was monitored by measuring the absorption and photoluminescence
spectra of the reaction mixture at regular intervals of time.
The temperature and the duration of growth determine the
final size of the particles. Yellow-emitting CdTe nanocrystals
with an average size of ca. 3 nm, for instance, were obtained
by heating the reaction mixture between 150 and 180 °C for a
few hours only. The largest particles were prepared by overnight
(10-12 h) heating at 200 °C. By this method, we obtained CdTe
nanocrystals with mean sizes ranging from 2.5 to 5 nm. They
show strong band-gap emission with quantum yields exceeding
30%. Depending on particle size, emission colors between green
and red are observed. CdTe nanocrystals of larger size (up to
app. 7.0 nm) were grown by the dropwise addition of mixed
Cd and Te precursors (the same amounts as used for the
synthesis itself). Before this additional injection, the reaction
mixture was cooled to 70 °C. After injection, the temperature
was raised to 100 °C for 3 h, with subsequent annealing at 180
°C. After completion of the particle growth and cooling the
reaction mixture to 50 °C, 20 mL of toluene was added to
the solution, and the mixture was left for 24 h at room
temperature under permanent stirring.