Supporting Information Cadmium deoxycholate: a new and efficient

1

Supporting Information

Cadmium deoxycholate: a new and efficient precursor for highly

luminescent CdSe nanocrystals

Arkajyoti Chakrabarty,† Sayantan Chatterjee† and Uday Maitra*†

†Department of Organic Chemistry, Indian Institute of Science, Bangalore, 560012, Karnataka,

India

*E-mail: [email protected]

Table of contents

1. ICP-OES analysis (Table 1).

2. Measurement and calculation of photoluminescence quantum yield (Table 2 and equation

S1).

3. Growth Kinetics and powder XRD pattern of CdSe nanocrystals (NCs) showing dot to rod

transformation (HDA/TOPO=45:55) (Fig. S1 and S2).

4. Experimental details, growth kinetics, size distribution, powder XRD and

photoluminescence behaviour of CdSe nanocrystals synthesized with precursor injection

method (injection temperature 240 oC, solvent 1-dodecanol) (Fig. S3-S5).

5. Additional TEM images.

6. Salient features of CdSe NCs synthesized in different synthetic routes.

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry CThis journal is © The Royal Society of Chemistry 2013

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1. ICP-OES analysis

Table 1. Characterization of cadmium deoxycholate by Inductively-coupled Plasma-

Optical Emission Spectrometry (ICP-OES) and C, H elemental analysis

ICP-OES Elemental analysis (%)

Calculated for C48H78O8Cd

% of Cd=12.6

Found

% of Cd=13.2

Calculated for C48H78O8Cd.3H2O

C=60.71, H=8.92

Found

C=60.87, H=8.88

Sample preparation of ICP-OES analysis. A known weight of cadmium deoxycholate (2-5 mg)

(or, CdSe nanocrystals capped with organic ligands) was digested with c. H2SO4 and 30% H2O2

(0.75 mL and 0.18 mL respectively) upon heating at 130 oC for 45 min. The sample solution was

cooled to room temperature and diluted to 50 mL with double-distilled water to prepare the

unknown sample solution. The concentration was found out from a standard calibration curve.


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2. Measurement and Calculation of photoluminescence quantum yield (PL QY)

The standard dyes used for PL QY measurements are listed below (Table 2).

Table 2. Dyes used in quantum yield measurements

Name λabs (nm)

λex(nm) λem(nm) QY (%)

Coumarin 153

425 445 528 53

Rhodamine 6G

528 499, 502

553 95

For PL QY measurement, the absorbance of the CdSe nanocrystals and the reference were

adjusted so that they are comparable and < 0.1 absorbance. units. Photoluminescence of the

nanocrystal and dye samples were recorded using the same excitation wavelengths. The

integrated area under the fluorescence curve was computed and the PL QY was calculated using

standard methods.

PL QY was calculated according to the following relation:

⁄ ⁄ / ,……………………(S.1)

where is the PL QY of the experimental sample, A is the integrated area under

fluorescence curve and η is the refractive index of the corresponding solvent. The error in the

QY measurement was meant to be ±5%.


3. G

tr

Fig. S1

showing

Fig. S2

HDA/T

Growth Kin

ransformat

1. Tempora

g dot to rod

2. Powder

TOPO 45:55

netics and p

tion (HDA/

l evolution

d transforma

XRD patte

5).

powder XR

/TOPO=45

n of UV-Vi

ation.

ern of CdS

RD pattern

:55) (cf. Fig

s (black) a

Se NCs sho

n of CdSe n

g. 5 in the m

and PL (blu

owing dot

nanocrystal

main text)

ue) spectra

to rod tran

ls showing

of CdSe n

nsformation

4

dot to rod

nanocrystals

n (Solvents

4

d

s

:


5

4. (a) Experimental details of CdSe nanocrystals synthesized with precursor injection

method (injection temperature 240 oC, solvent 1-dodecanol)

A typical synthesis is as follows. Se powder (0.079 g, 1.0 mmol) was dissolved in TOP (0.6

mL, 1.34 mmol) and 1-dodecanol (0.4 mL) by heating at 90 oC for 10 min. The resulting clear

solution was cooled to room temperature, degassed under vacuum (1×10-3 Torr) and kept under

Ar. Cadmium deoxycholate (0.095 g, 0.1 mmol) and deoxycholic acid (0.255 g, 0.6 mmol) were

suspended in dodecanol (5.2 mL) followed by the addition of a mixture of TOPO (0.5 g, 1.3

mmol) and HDA (0.25 g, 1.0 mmol) at room temperature. The solution was heated with stirring

at 55 oC for 25 min while degassing under vacuum (1×10-3 Torr). The resulting clear solution

was heated at a rate of ~10 oC/min under a flow of Ar. At 240 oC, the room temperature TOPSe

solution was rapidly injected into the cadmium precursor solution and the reaction was

monitored carefully by withdrawing aliquots (0.1 mL) at regular time intervals and diluting with

chloroform (2 mL). The nanocrystals were further purified by precipitation using acetone-

methanol (5:1) and separated by centrifugation and decantation. The purified nanocrystals were

dispersed in chloroform and kept for further studies.


(b) G

Fig. S3

with pre

Growth kine

. Temporal

ecursor inje

etics (cf. Fi

evolution o

ection metho

g. 7 in the m

of UV-Vis

od (injection

main text)

(black) and

n 240 oC, so

d PL (blue)

olvent 1-do

of CdSe na

decanol).

anocrystals

6

synthesized

6

d


(c) C

Fig. S4

growth

1-dodec

size dis

dSe NCs si

4. (a) UV-V

reaction of

canol as sol

tribution in

ize distribu

Vis (black) a

f CdSe nano

lvent; b) TE

(b), (d) pow

ution and po

and PL (blu

ocrystals pr

EM images

wder XRD p

owder XRD

ue) spectra

repared with

of 3.2 nm

pattern show

D pattern (

of an aliquo

h precursor

diameter C

wing zinc b

(cf. Fig. 7 in

ot withdraw

injection m

dSe nanocr

blende cryst

n the main

wn after 219

method at 24

rystals; c) h

al structure

7

text)

9 sec of the

40 oC using

histogram of

.

7

e

g

f


(d) Ph

Fig. S5

oC) sho

half-ma

hotolumine

5. Photolum

owing temp

axima (midd

escence beh

minescence b

oral evoluti

dle panel) a

haviour (cf

behavior of

ion of phot

nd peak pos

f. Fig. 8 in t

f CdSe NCs

toluminesce

sition (botto

the main te

(synthesize

ence quantu

om panel).

ext)

ed with pre

um yield (to

cursor injec

op panel), fu

8

ction at 240

full-width at

8

0

t


5. A

Fig. S

(HDA/T

injectio

injectio

Additional T

S6. (a) an

TOPO=62:3

on at 300 o

on at 240 oC

TEM image

nd (b) sp

38); (c) an

oC (HDA/T

in 1-dodec

es

pherical Cd

nd (d) CdS

TOPO=45:5

canol.

dSe NCs

Se NCs w

5); (e) and

synthesize

with rod-lik

d (f) CdSe

ed with i

ke morpholo

NCs synth

injection a

ogy synthe

hesized with

9

at 300 oC

esized with

h precursor

9

C

h

r


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6. Salient features of the CdSe NCs synthesized in different synthetic routes using

cadmium deoxycholate

The results of the different synthetic routes from cadmium deoxycholate to CdSe NCs are

summarized in Table 3.

Table 3. Emission colour, Solvent system, reaction mode, temperature of injection/growth,

crystal structure and shape of the NCs in different synthetic schemes.

Emission colour

Solvent system

Precursor injection

mode

Temperature of injection/growth

Crystal Structure & shape

a) Orange-red

HDA-TOPO-TOP; HDA/TOPO=62:38

YES 300 oC (injection) 290 oC (growth)

wurtzite/spherical

b) Green-orange

HDA-TOPO-TOP; HDA/TOPO=45:55

YES 300 oC (injection) 290 oC (growth)

wurtzite/dot-rod

c) Blue-yellow

1-dodecanol NO 170-240 oC zinc blende/spherical

d) Blue-yellow

1-dodecanol YES 240 oC zinc blende/spherical


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Supporting Information Cadmium deoxycholate: a new and efficient