In . J. Elec ochem. Sci., 11 (2016) 175 - 188
In e na ional Jou nal o
ELECTROCHEMICAL
SCIENCE
www.elec ochemsci.o g
UV Tuning o Cadmium Tellu ide Quan um Do s (CdTe QDs) –
Assessed by Spec oscopy and Elec ochemis y
Lukas Nejdl1,2, Lukas Rich e a1,3, Kledi Xhaxhiu4, Rena a Kenso a1,3, Ji i Kud 1,3,
B anisla Ru kay-Nedecky1,3, Jind ich Kynicky1,2, Do o a Waw zak5, Voj ech Adam1,3, Rene Kizek1,3,
Pa el Kopel1,3,*
1Cen al Eu opean Ins i u e o Technology, B no Uni e si y o Technology, Technicka 3058/10, CZ-
616 00 B no, Czech Republic - Eu opean Union
2Depa men o Geology and Pedology, Mendel Uni e si y in B no, Zemedelska 1, CZ-613 00 B no,
Czech Republic - Eu opean Union
3Depa men o Chemis y and Biochemis y, Mendel Uni e si y in B no, Zemedelska 1, CZ-613 00
B no, Czech Republic - Eu opean Union
4Depa men o Chemis y, Facul y o Na u al Sciences, Uni e si y o Ti ana, Bl . Zog I, No.2/1,
1001, Ti ana, Albania
5Ins i u e o Chemis y, En i onmen al P o ec ion and Bio echnology, Jan Dlugosz Uni e si y o
Czes ochowa, A mii K ajowej 13/15, PL-42201 Czes ochowa, Poland
*E-mail: paulko@cen um.cz
Recei ed: 23 Sep embe 2015 / Accep ed: 8 Oc obe 2015 / Published: 1 Decembe 2015
In his wo k, he elec ochemical analysis (po en iome ic s ipping analysis – PSA, cyclic
ol amme y – CV) and e alua ion o luo escence p ope ies o cadmium ellu ide quan um do s
(CdTe QDs) co e ed by me cap osuccinic acid (MSA) we e pe o med. Using CV i was ound ha
a e age alue o ΔE o QDs is lowe han 0.059 V and I is in di ec co ela ion wi h squa e oo o scan
a es, he e o e i can be assumed ha his sys em ep esen s a he e e sible han quasi- e e sible
p ocess. Fu he , i was ound ha nea ly 1.4 elec ons a e exchanged in bo h cases, which
co esponded wi h expec ed wo-elec on ans e . Fluo escence analysis showed ha UV adia ion
(254 and 312 nm) signi ican ly changes luo escence p ope ies o CdTe QDs in ime 0 – 60 min. I
was ound ha a e 5 min o UV i adia ion (λ = 312 nm) he luo escence in ensi y inc eased by 37%
and a λ = 254 nm he inc ease in luo escence in ensi y was e en highe , by 45% (compa ed o he
con ol wi hou i adia ion). UV adia ion also caused a shi in he emission maximum o CdTe QDs
in ange 2 – 70 nm. This wo k opens up new ways o uning he op ical p ope ies o QDs.
Keywo ds: Cyclic ol amme y; Fluo escence analysis; Nanopa icles; Po en iome ic s ipping
analysis; Quan um do s; Syn hesis; UV adia ion; UV uning;
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1. INTRODUCTION
Nano echnology is one o he mos ad anced disciplines. One o he main a eas o
nano echnology is he syn hesis and cha ac e iza ion o a ious ypes o nanopa icles o a wide
spec um o applica ions [1-3]. En y in o he nano wo ld has opened up new possibili ies o he use o
luo escen nanoc ys als be e known as quan um do s (QDs) and u iliza ion o hei unique p ope ies
[4]. QDs we e i s epo ed by Alexey Ekimo in 1981 in a glass ma ix and hen in colloidal solu ions
by Louis E. B us in 1985 [5]. QDs we e one o he i s nanopa icles o be in eg a ed wi hin he
biological sciences ha we e used o imaging o acking mac omolecules/cells in cell/ issue [6]. The
popula i y o QDs is mainly due o a wide a ie y o di e en ypes o p epa a ion and
unc ionaliza ion o hei su ace [7-10]. QDs e ain pa o he p ope ies o he ma e ial, om which
hey a e made, bu also ake o e he new p ope ies ha a e ela ed o hei size (size-dependen
op ical abso p ion and emission) [11]. Fo biological applica ions, he mos equen ly used a e CdSe,
CdSe/ZnS o CdTe, CdTe/CdS nanoc ys als [12-19]. The pa icles a e gene ally made o hund eds o
housands o a oms mainly o g oup II and VI elemen s (CdSe and CdTe QDs) o g oup III and V
elemen s (InP and InAs QDs) [20].
The mos popula me hods o QDs syn hesis a e o ganome allic syn hesis, aqueous ou e (low-
empe a u e eac ion) and biosyn hesis [6]. An in e es ing complemen o hese me hods can be pos -
syn hesis o QDs by exposu e o he UV adia ion. In his way, he su ace o QDs can be ac i a ed and
op ical p ope ies o QDs can be con olled ( uned). The abili y o UV ligh o change he con o ma ion
o complexes was s udied in ou p e ious wo k [21]. I has been demons a ed ha UV adia ion
ac i a es luo escence o zinc(II) complexes. The ligh -induced con ol o a ious ype o emulsions
(oil o wa e con inuous medium) s abilized by an app op ia e combina ion o wo polyelec oly e
su ac an s was desc ibed [22]. Fu he mo e, a numbe o pho oca aly ically ac i e nanopa icles has
been e iewed e.g. TiO2 nano ods [23], ZnO nanopa icles [24] and o he s [25,26]. Co osion o he
ou e sphe e o nanopa icles caused by pho ooxida ion leading o oxic ion elease, o ma ion o
eac i e oxygen species (ROS) o induc ion o geno oxic s ess was epo ed [27-29]. Yin e al. showed
ha he oxic e ec o PbSe QDs unde UV i adia ion is caused by elease o Pb(II) and gene a ion o
ROS, inducing DNA damage [30]. Pho oca aly ic echnique can be used o me als emo al o
ans o ma ion o ee ions o he less oxic species o hei deposi ion on he semiconduc o ca alys
su ace o me als eco e y [31]. In ou expe imen s, we ha e ocused on he elec ochemical s udy o
CdTe QDs wi h me cap osuccinic acid on su ace and subsequen luo escen analysis o QDs exposed
o UV adia ion a wo wa eleng hs λ = 254 and λ = 312 nm in ime in e als 0 – 60 minu es. Fo
elec ochemical in es iga ion o QDs CV and PSA we e chosen. By s udying he da a ob ained om
he CV e e sibili y o elec ode eac ions, numbe o elec ons ans e ed, he kine ics o he
indi idual eac ion s eps, s abili y o he esul ing in e media es, adso p ion and deso p ion on he
elec ode ma e ial om he elec ode can be de e mined. Because o i s simplici y and economy, PSA
is conside ed a e y use ul elec ochemical echnique o me al aces de e mina ion [32-37]. This
highly sensi i e mic oanaly ical echnique was used e.g. o hea y me al low concen a ion
de e mina ion in soil o in he bal d ugs [38-40]. T aces o soluble lead in glasswa e we e de e mined
by his me hod oo [41]. Ano he applica ion o PSA me hod is he de e mina ion o me als in human
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ee h and den al ma e ials [42,43]. The simples PSA modi ica ion uses dissol ed oxygen as he
oxidizing agen . Thus, he con amina ion isk a ising om he applica ion o some ex e nally added
oxidizing agen s [44-46]is educed. In his a icle, a signi ican abili y o UV ligh o al e he
luo escence p ope ies o CdTe QDs was desc ibed, which can be used o imp o e he quan um yield
o QDs, o adjus ing ( uning) he emission maxima o he pa icula applica ion.
2. EXPERIMENTAL PART
2.1 Chemicals
Wo king solu ions like bu e s and s anda d solu ions we e p epa ed daily by dilu ing he s ock
solu ions. S anda ds and o he chemicals we e pu chased om Sigma-Ald ich (S . Louis, MO, USA) in
ACS pu i y unless no ed o he wise.
2.2 P epa a ion o CdTe QDs
CdTe QDs we e p epa ed acco ding o he ollowing p o ocol. B ie ly, 10 mL o cadmium(II)
ace a e (5.34 mg·mL-1) and 1.0 mL o me cap osuccinic acid solu ion (60.0 mg·mL-1) we e mixed wi h
76.0 mL o deionized wa e on a magne ic s i e . Subsequen ly 1.8 mL o ammonia (1.0 M) solu ion
was added o he eac ion mix u e. Then 1.5 mL o sodium ellu i e (4.43 mg·mL-1) was also added
unde con inuous s i ing and la e 40 mg o sodium bo ohyd ide was added. The solu ion was s i ed
o a ound 2 h un il he bubble o ma ion inished and subsequen ly he olume o he solu ion was
dilu ed up o 100 mL wi h deionized wa e . Volume o 2.0 mL o p epa ed solu ion was aken in a
small glass essel and hea ed a 100 °C, 300 W o 20 min ( amping ime 10 min) unde mic owa e
i adia ion (Mul iwa e 3000, An on-Paa GmbH, G az, Aus ia) and inally he p epa ed CdTe QDs
we e s o ed in he da k a 4 °C.
2.3 De e mina ion o cadmium by a omic abso p ion spec ome y
Cadmium concen a ion was de e mined using 280Z Agilen Technologies a omic abso p ion
spec ome e (Agilen , San a Cla a, CA, USA) wi h elec o he mal a omiza ion. Cadmium
ul asensi i e hollow ca hode lamp (Agilen ) was used as he adia ion sou ce (lamp cu en 4 mA).
The spec ome e was ope a ed a 228.8 nm esonance line wi h spec al bandwid h o 0.5 nm. The
sample (10 µL) was injec ed in o he g aphi e cu e e. The low o a gon ine gas was 300 mL·min-1.
Zeeman backg ound co ec ion was used wi h ield s eng h 0.8 T. Cadmium was de e mined in he
p esence o palladium chemical modi ie .
2.4 Elec ochemical measu emen (PSA and CV)
De e mina ion o Cd(II) and CdTe QDs by PSA and CV was pe o med wi h 797 VA
Compu ace ins umen (Me ohm, Swi ze land), using a s anda d cell wi h h ee elec odes. A hanging
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me cu y d op elec ode (HMDE) wi h a d op a ea o 0.4 mm2 was employed as he wo king elec ode.
An Ag/AgCl/3M KCl elec ode was used as he e e ence and ca bon elec ode se ed as auxilia y. Fo
da a p ocessing 797 VA Compu ace so wa e by Me ohm CH was employed. The analyzed samples
we e deoxygena ed p io o measu emen s by pu ging wi h a gon (99.999%). De e mina ion o Cd(II)
and CdTe QDs was pe o med wi h ace a e bu e (0.2 M CH3COONa and CH3COOH, pH 5) as a
suppo ing elec oly e. The suppo ing elec oly e was exchanged a e each analysis. Volume o
sample 15 µL, o al olume o measu emen cell 2 mL (15 μL o sample + 1985 μL ace a e bu e ).
The pa ame e s o he measu emen by PSA we e as ollows: ini ial po en ial o ˗0.70 V, end po en ial
˗0.25 V, numbe o cycles 1, deoxygena ing wi h a gon 60 s, po en ial limi ˗0.25 V, maximal ime
360 s (p e- ea men used pa ame e s: cleaning po en ial ˗0.70 V, cleaning ime 60 s, deposi ion
po en ial ˗0.70 V, deposi ion ime 600 s, equilib a ion ime 15 s). Measu emen s we e ca ied ou a
25 ± 1 °C. CV was ca ied wi h same elec ochemical appa a us as in he case PSA was used. The
pa ame e s o he measu emen we e as ollows: ini ial po en ial o ˗0.80 V, i s e ex po en ial
˗0.20 V, second e ex po en ial ˗0.80 V, deoxygena ing wi h a gon 90 s, deposi ion 0 s, ol age s ep
5 mV, scan a e 6.25 - 400 mV·s-1, deposi ion po en ial ˗0.80 V.
2.5 Fluo escence analysis
Fluo escence was acqui ed by mul i unc ional mic opla e eade Tecan In ini e 200 M PRO
(TECAN, Swi ze land). Wa eleng h 360 nm was used as an exci a ion adia ion and he luo escence
scan was measu ed wi hin he ange om 400 o 850 nm pe 2-nm s eps. The de ec o gain was se o
65. The samples we e placed in UV- anspa en 96 well mic opla e wi h la bo om by CoS a
(Co ning, USA). To each well 50 μL o sample was placed. All measu emen s we e pe o med a
25 °C con olled by Tecan In ini e 200 PRO (TECAN, Swi ze land). The QDs we e exposed o UV
adia ion a 254 and 312 nm using ansillumina o (Vilbe Lou ma , Ma ne-la-Vallee Cedex, F ance).
The sample a ea is 20 × 20 cm illumina ed by 6 UV emi ing ubes wi h powe o 15 W each. The
in ensi y o UV adia ion incoming o he UV- anspa en 96-well mic opla e was eco ded by
ins umen o he de e mina ion o op ical powe (PM100D, senso SV120VC, Tho labs Inc., New on,
NJ, USA). Based on hese measu emen s he in ensi y o incoming UV ene gy in o he sample was
de e mined: E = 3.12 mW (λ = 312 nm) and E = 4.18 mW (λ = 254 nm).
2 .6 Pa icle size and ze a-po en ial analysis
Ze asize MALVERN, Mal e n Ins umen s L d. Wo ces e shi e WR14 1XZ, Uni ed Kingdom
was used.
2.6.1 Ze a po en ial assessmen
The pa icle size measu emen s we e pe o med conside ing he same e ac ion index and
abso p ion coe icien as desc ibed in pa icle size measu emen s. Fu he mo e, he measu ing
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pa ame e s such as, empe a u e and iscosi y we e he same as in pa icle size measu emen s (see
below). Calcula ions conside ed he diminishing o pa icles concen a ion based Smoluchowsky
model, wi h a F(κa) o 1.50 and an equilib a ing ime o 120 s. Fo he measu emen s, a disposable
cell DTS1070 was employed. In each case, he measu emen du a ion depended on he numbe o uns,
which a ied be ween 20 and 40. The measu emen s we e ca ied ou in iplica es and we e pe o med
unde he au oma ic se ing o a enua ion and ol age selec ion.
2.6.2 Pa icle size assessmen (dynamic ligh sca e ing)
The pa icle size measu emen s we e pe o med conside ing a e ac ion index o he dispe si e
phase o 3.00 and 1.33 o he dispe si e en i onmen . The abso p ion coe icien in bo h cases was 10-
3. The measu ing empe a u e was se a a cons an alue o 25 °C, while he iscosi y was 0.8872 cP.
Fo each measu emen , disposable cu e es ype ZEN 0040, we e used, con aining 40 µL o sample.
The equilib a ion ime was 120 s, a a measu emen angle o 173° backsca e . All measu emen s we e
iplica e (p < 0.05) and he da a was exp essed as he a e age alue.
3. RESULTS AND DISCUSSION
3.1 Elec ochemical beha io o Cd(II) and CdTe QDs
QDs and cadmium s anda d we e s udied and cha ac e ized using CV and PSA. CV is popula
o i s ela i e simplici y and i s high in o ma ion con en . I is used mos o en as a diagnos ic ool o
elucida ing elec ode mechanisms. The ad an age o PSA echnique is pu po ed o be i s lowe
suscep ibili y o in e e ences om adso p ion o o ganic molecules on he elec ode su ace
(deposi ion s ep is iden ical o ha in he anodic s ipping echniques) [47]. Fi s , s ock solu ions o
Cd(II) and CdTe QDs we e uni ed acco ding o o al concen a ion o Cd(II) by a omic abso p ion
spec ome y (AAS) and elec ochemically analyzed.
3.1.1 Cyclic ol amme y o Cd(II) and CdTe QDs
Cyclic ol ammog ams o 3 µM Cd(II) solu ion a di e en alues o scan a e (6.25 –
400 mV·s-1) we e eco ded, Fig. 1 A. Fu he , he plo ed Ipc (ca hodic cu en ) and Ipa (anodic
cu en ) on scan a e (Fig. 1 B) and scan a e oo ν½, Fig. 1 C. In he case o CdTe QDs was ollowed
in he same way. Cyclic ol ammog ams o 3 µM CdTe QDs solu ion a di e en alues o scan a e
(6.25 – 400 mV·s-1) we e eco ded (Fig. 1 B) and subsequen ly Ipc (ca hodic cu en ) and Ipa (anodic
cu en ) on scan a e (Fig. 1 E) and scan a e oo ν½ (Fig. 1 E) we e e alua ed. Obse ed alues a e
shown in he ables, Tab. 1 A Cd(II) and B CdTe QDs. In all cases, linea dependence was obse ed.
Gi en ha he a e age alue ΔE is less han 0.059 V, while he I alue is di ec ly p opo ional o he
squa e oo o scan a e, i can be assumed ha he in es iga ed edox e en s Cd(II) and CdTe QDs
aking place a he elec ode a e a he e e sible han quasi e e sible. The numbe o exchanged

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elec ons a edox e en s Cd(II) and CdTe QDs elec ode is acco ding o he ela ion (ΔEp = Epa –
Epc = 2.303 RT/nF) equal in bo h cases and eaches app oxima ely 1.4, e lec ing he an icipa ed
ans e o wo elec ons. The dependence o he CV analy ical signal o Cd(II) and CdTe QDs scan
a e oo ga e he ollowing equa ions:
Ipc (nA) = 9.6 ν½ (mV½·s˗½), R2 = 0.9982, n = 3
Cd(II)
Ipa (nA) = ˗6.3 ν½ (mV½·s˗½), R2 = 0.9348, n = 3
Cd(II)
Ipc (nA) = 8.2 ν½ (mV½·s˗½), R2 = 0.9967, n = 3
CdTe QDs
Ipa (nA) = ˗5.8 ν½ (mV½·s˗½), R2 = 0.9373, n = 3
CdTe QDs
Figu e 1. (A) Cyclic ol ammog ams o Cd(II) measu ed a di e en alues o scan a e (6.25 –
400 mV·s-1). Dependence (Cd(II)) o Ipc and Ipa on scan a es (B) and squa e oo o scan a es
ν½ (C). (D) Cyclic ol ammog ams o CdTe measu ed a di e en alues o scan a e (6.25 –
400 mV·s-1). Dependence (CdTe) o Ipc and Ipa on scan a es (E) and squa e oo o scan a es
ν½ (F). Fo all elec ochemical expe imen s 3 µM Cd(II) and 3 µM CdTe solu ions we e used.
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Table 1. Elec ochemical pa ame e s based on cyclic ol ammog ams o (A) 3 µM Cd(II) and (B)
3 µM CdTe QDs.
3.1.2 Po en iome ic s ipping analysis (PSA) o Cd(II) and CdTe QDs
Figu e 2. (A) PSA ol ammog ams o Cd(II) and (B) de ail o ol ammog ams (zoom). (C) The
calib a ion cu e o Cd(II) in he linea ange 0.03 – 240 µM. (D) PSA ol ammog ams o
CdTe QDs and E) de ail o ol ammog ams (zoom). (F) The calib a ion cu e o CdTe QDs in
he same ange as Cd(II).
Elec ochemical esponses o di e en concen a ions o Cd(II) and CdTe QDs we e compa ed
using PSA. This me hod enables mo e p ecise analysis o samples compa ed o di e en ial pulse o
squa e wa e ol amme y, due o he lowe in luence o a ious in e e en s on he measu emen [47].
A i s , he linea i y and ep oducibili y o he PSA analy ical signal o Cd(II) was checked. The
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analy ical signal was ound o be a linea unc ion o he Cd(II) concen a ions wi hin he concen a ion
ange o 0.03 – 240 µM (Fig. 2 A and zoom B). The dependence o he PSA analy ical signal on he
mass concen a ion o Cd(II) in sample ga e he ollowing equa ion:
d /dV (s·V-1) = 26.24 cCd(II) (µM) ˗ 30.69, R2 = 0.9963, n = 3 (Fig. 2 C).
In he case o CdTe QDs, measu emen was pe o med in he same way. Fig. 2 D shows he
ol ammog ams o CdTe QDs and zoom, Fig. 2 E. The dependence o he PSA analy ical signal on he
mass concen a ion o CdTe QDs in sample ga e he ollowing equa ion:
d /dV (s·V-1) = 2.816·101 cCd(II) (µM) - 10.060, R2 = 0.9989, n = 3 (Fig. 2 F)
Acco ding o he high alues o he coe icien s o de e mina ion (R2 = 0.9963 and 0.9989 o
Cd(II) and CdTe QDs, espec i ely), i can be concluded ha he e was a e y good linea i y o he
PSA analy ical signals wi hin he examined concen a ion anges o cadmium. This me hod con i med
he esul s om CV, his means ha he elec ochemical beha io o Cd(II) and CdTe QDs is simila .
3.2 UV in e ac ion wi h CdTe QDs (colo uning)
Fluo escence spec oscopy was employed o moni o ing he in e ac ion o UV adia ion wi h
CdTe QDs in ime. Emission spec a in he ange o 400 – 800 nm wi h exci a ion wa eleng h o
360 nm a empe a u e 25 °C we e ob ained. Condi ions men ioned abo e we e used o all
measu emen s. CdTe QDs we e exposed o UV adia ion (λ = 312 and λ = 254 nm) o 5 minu es in
he ansillumina o and emission spec a o samples we e measu ed in i e-minu e ime in e als up
o 60 minu es . The samples we e placed in UV- anspa en 96 well mic opla e wi h la bo om. A e
i adia ion, he luo escence p ope ies o QDs ( luo escence in ensi y and emission maximum) we e
moni o ed immedia ely. This p ocess was epea ed wel e imes o obse e he UV dose dependency.
Fi s , ansillumina o was se on 312 nm. A e ha , samples (50 µL o 1 mM QDs in UV- anspa en
96 well mic opla e) we e inse ed in o he ansillumina o .
I was ound ha a e 5 min o UV i adia ion (λ = 312 nm) he luo escence in ensi y
inc eased by 37% (compa ed o he con ol wi hou i adia ion) and he colo changed om g een o
ligh g een, Fig. 3 A. Ano he i e-minu e i adia ion caused an inc ease in luo escence in ensi y
u he by 9% and he colo u ned o yellow-g een. Ano he en-minu e i adia ion caused an inc ease
in luo escence in ensi y by app oxima ely 1% and he colo u ned yellow. Each subsequen
i adia ion caused a dec ease in luo escence in ensi y o QDs by 10%. The las wo UV exposu es in
ime o 55 and 60 minu es caused a colo change o b igh o ange (in 55 minu es) and o ange (in
60 minu es). Fu he , he dependence o he UV adia ion on he change o he emission maximum o
QDs was obse ed, Fig. 3 B. In con ol QDs (wi hou i adia ion), he emission maximum a
λem = 522 nm was ound. Fi e minu es o UV i adia ion (λ = 312 nm) caused a shi in emission
maximum o 4 nm. Ano he i e-minu e exposu e o UV adia ion caused a shi in emission
maximum o ano he 8 nm. Ano he en-minu e i adia ion caused a shi by 14 nm and ano he en-
minu e i adia ion by 16 nm. A e 60 minu es o UV i adia ion o QDs emission maximum o
λem = 570 nm was achie ed. Second, ansillumina o was se on 254 nm and he same measu emen s
we e ca ied ou as in he p e ious case.
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I was ound ha a e 5 min o UV i adia ion (λ = 254 nm) he luo escence in ensi y
inc eased by 45% (compa ed o he con ol wi hou i adia ion) and he colo changed om g een o
ligh g een, Fig. 3 C. Ano he i e-minu e i adia ion caused a dec ease in luo escence in ensi y by
12% and he colo was yellow. Each addi ional adia ion exposu e caused a sligh dec ease
(app oxima ely by 3.5%) o QDs luo escence in ensi y. UV exposu e in ime o 35, 40, 45 and
50 minu es caused a colo change o b igh o ange (in 35 minu es) and o ange (in 40, 45, 50 minu es).
The las wo UV exposu es in ime o 55 and 60 minu es caused a colo change o b igh ed. The shi
in emission maximum o QDs depending on he UV i adia ion leng h had a simila end as in he
p e ious case, Fig. 3 D. Fi e minu es o UV i adia ion (λ = 254 nm) caused a shi in emission
maximum o 4 nm. Ano he i e-minu e exposu e o UV adia ion caused a shi in emission
maximum o ano he 8 nm. Ano he en-minu e i adia ion caused shi by 36 nm and ano he en-
minu e i adia ion by 18 nm. A e 60 minu es o UV i adia ion o QDs emission maximum
λem = 592 nm was achie ed.
The wo gene al exis en s a egies (con ol size) o nanoc ys al p epa a ions a e an
o ganome allic syn hesis based on he high- empe a u e he molysis o he p ecu so s [48,49] and he
syn hesis in an aqueous medium [50,51].
Figu e 3. (A) The e ec o UV adia ion (λ = 312 nm, E = 3.12 mW) on he change in luo escence
p ope ies o 1 mM QDs and (B) emission maximum o QDs du ing exposu e o UV adia ion
(0 – 60 min). (C) The e ec o UV adia ion (λ = 254 nm, E = 4.18 mW) on he change in
luo escence p ope ies o QDs and (D) emission maximum o QDs du ing exposu e o UV
adia ion 0 – 60 min. (E) Schema ic ep esen a ion o he e ec o UV adia ion on he inc ease
in size o CdTe QDs.
The size and he emission colo o QDs can be uned by a ying he e lux ime [52], g ow h
empe a u es [53] o pH change [54]. The pho oluminescence o he g aphene QDs can be due o
cha ge ans e s be ween unc ional g oups o g aphene QDs [55]. The echnique p esen ed in his
pape can be used o he easy, inexpensi e and as syn hesis o he pos -syn hesis ( uning) o CdTe
QDs s abilized by MSA. P obable mechanism is ha he UV ligh causes an inc ease in size o
agg ega ion o CdTe QDs (Fig. 3 E), which lead o a change in hei op ical p ope ies. Inc ease in size