Ultrafast Carrier Dynamics of Photo-Induced Cu-Doped CdSe Nanocrystals

Abstract

The understanding of ultrafast carrier relaxation process in doped semiconductor quantum dots (QDs) is very important for their potential applications in light-emitting diodes, optoelectronics. Here, we have studied the change in electronic properties of Cu-doped CdSe QDs upon light illumination. The light-induced effect leads to the enhancement of the band edge decay time and reduces the decay time of the dopant emission due to photocorrosion of Cu-doped CdSe QDs. The bleaching recovery kinetics and the hot electron cooling dynamics have been studied by using femtosecond transient absorption spectroscopy. It is observed that the electron cooling process of doped CdSe QDs is dependent on the dopant concentration and the cooling kinetics of doped CdSe QDs are found to be slower than undoped QDs. After light irradiation, the cooling processes of hot electron and recovery process in doped systems are modified.

Exciton recycling via InP quantum dot funnels for luminescent solar concentrators

“…3(c)) features an initial growth time τg (τg = 3.3 and 2.4 ps in undoped and doped QDs, respectively) due to the relaxation of the hot excitons to the band edges, followed by a bi-exponential decay characterized by decay times τ1 and τ2. The decay times τ1 and τ2 describe fast decay due to intermediate trapping states, as observed in earlier studies [38,39]. In addition, a third longer decay exists over ns time scales due to inter-band electron-hole recombination.…”

Effect of Copper Doping on Electronic Structure and Optical Absorption of Cd33Se33 Quantum Dots

“…In the visible region (the main figure of Figure 6), just one Cu dopant induces high-intensity absorption peaks in the range of 408-502 nm for CuCd 32 Se 33 (S), 380-428 nm for CuCd 32 Se 33 (C I ), and 445-574 nm for CuCd 32 Se 33 (C II ). In experiments, the enhancement of absorption spectra in the wavelength range between 390 and 600 nm was also observed in Cu-doped CdSe NCs [19,22,31]. When two or three Cu atoms are doped, absorption peaks are relatively weaker within the same wavelength range.…”

“…By such doping, new energy levels could be introduced into the bandgap of the host NCs, which can exchange charges with the valence band or the conduction band, thereby significantly influence their electronic and optical properties. Copper exhibits variable valences (+1 and +2) and has become a promising doping element in II-VI semiconductor NCs to modify the electronic and optical properties for their desirable applications [2,17,[19][20][21].…”

Observation of a phonon bottleneck in copper-doped colloidal quantum dots

“…Although not reported in refs. 35,36 , we suspect the QDs used there might have a much slower hole capturing rate, thus allowing hot electron relaxation via energy transfer to the hole. This is likely due to the low Cu concentration in the QDs used there, because the hole transfer rate should roughly scale with the number of available Cu dopants inside the QD.…”

“…Gamelin et al studied carrier recombination dynamics in n -type Cu-doped CdSe/CdS QDs and found an ultrafast (~260 ps), Auger-dominated negative trion recombination pathway involving two band edge electrons and a Cu-captured hole 34 , but no hot carrier relaxation dynamics was reported in this work. Slightly longer-lived hot electrons in Cu:CdSe QDs as compared to CdSe QDs (700 fs vs. 400 fs) were reported in the works by Ghosh et al 35 and by Patra et al 36 , but such a marginal improvement in hot electron lifetime is not sufficiently impactful for hot electron devices. Thus, in order to realize long-lived hot electrons in Cu:QDs, it is essential to optimize the hole capturing process by Cu dopants and to directly measure the rate of this process and compare it with hot electron relaxation rate.…”