TY - JOUR
T1 - Photoluminescence characteristics of CdSe quantum dots
T2 - Role of exciton-phonon coupling and defect/trap states
AU - Kushavah, Dushyant
AU - Mohapatra, P. K.
AU - Ghosh, Pintu
AU - Singh, Mamraj
AU - Vasa, P.
AU - Bahadur, D.
AU - Singh, B. P.
N1 - Publisher Copyright:
© 2017 IOP Publishing Ltd.
PY - 2017/7
Y1 - 2017/7
N2 - In this paper, we report temperature dependent photoluminescence (PL) characteristics of CdSe colloidal QDs with average diameter ∼2.8 nm. Temperature dependence of strongly confined exciton PL peak position, linewidth and intensity were investigated in 30 K to 300 K temperature range. Our studies reveal nearly four times weaker exciton-LO phonon coupling than bulk CdSe crystal. Theoretically, it should be vanishingly small due to near identical electron and hole charge distributions in strongly confined QDs. On the other hand, exciton-acoustic phonon coupling is an order of magnitude larger than its bulk counterpart. Observed finite value of exciton-LO phonon coupling and enhanced exciton-acoustic phonon coupling are due to piezoelectric strain fields. PL intensity exhibits anomalous behavior in the temperature range 100-230 K. This has been explained by thermally activated detrapping of the charge carriers trapped in the potential wells formed at the interface adjoining dislocations/stacking faults developed during the synthesis process. Above 230 K, PL is partially quenched by thermal escape of charge carriers from luminescing exciton state to higher lying nonluminescing states.
AB - In this paper, we report temperature dependent photoluminescence (PL) characteristics of CdSe colloidal QDs with average diameter ∼2.8 nm. Temperature dependence of strongly confined exciton PL peak position, linewidth and intensity were investigated in 30 K to 300 K temperature range. Our studies reveal nearly four times weaker exciton-LO phonon coupling than bulk CdSe crystal. Theoretically, it should be vanishingly small due to near identical electron and hole charge distributions in strongly confined QDs. On the other hand, exciton-acoustic phonon coupling is an order of magnitude larger than its bulk counterpart. Observed finite value of exciton-LO phonon coupling and enhanced exciton-acoustic phonon coupling are due to piezoelectric strain fields. PL intensity exhibits anomalous behavior in the temperature range 100-230 K. This has been explained by thermally activated detrapping of the charge carriers trapped in the potential wells formed at the interface adjoining dislocations/stacking faults developed during the synthesis process. Above 230 K, PL is partially quenched by thermal escape of charge carriers from luminescing exciton state to higher lying nonluminescing states.
KW - CdSe quantum dots
KW - Exciton-phonon coupling
KW - Temperature dependent photoluminescence
UR - http://www.scopus.com/inward/record.url?scp=85027095392&partnerID=8YFLogxK
U2 - 10.1088/2053-1591/aa7a4f
DO - 10.1088/2053-1591/aa7a4f
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AN - SCOPUS:85027095392
SN - 2053-1591
VL - 4
JO - Materials Research Express
JF - Materials Research Express
IS - 7
M1 - 075007
ER -