Tunable dual emission in type-I/type-II CdSe/CdS/ZnSe nanocrystals

N. X. Ca, N. T. Hien, P. M. Tan, T. L. Phan, L. D. Thanh, P. V. Do, N. Q. Bau, V. T.K. Lien, H. T. Van

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We have used wet chemical methods to fabricate colloidal CdSe/CdSm/ZnSen core/intermediate/shell (C/I/S) nanocrystals (NCs), where m = 1 and 2 and n = 1–4 are the number of monolayers. The growth was monitored by using Raman and UV–vis spectroscopy, which demonstrated the formation of correct CdSe/CdSm/ZnSen C/I/S NCs. X-ray diffraction studies proved single-phase NCs crystallized in the zincblende-type structure. Photoluminescence (PL) studies have indicated that after photoexcitation C/I/S NCs generate simultaneously type-I and type-II emissions, namely E I and E II , associated with CdSe/CdSm and CdSm/ZnSen structures, respectively. For a specific value of m = 2, we have found the redshift of both E I and E II emissions when n is increased from 1 to 4. The PL studies versus the laser-excitation power (P ex ) up to about four orders of magnitude allow us to identify the origin of two emissions. A large blueshift of the E II peak is ascribed to the band bending effect resulting from the spatially separated photoexcited carriers in type-II NCs. It appears that the dependence of the E II peak on the cube root of P ex (P ex 1/3 ) is linear while that of the E I peak on P ex 1/3 is almost constant. In this work, we also point out that the emission intensity (I) of E I and E II can be tuned by changing the values of n and P ex , where I obeys a power law I∝P ex k , with k = 0.7–1.0 dependent on the emission type. The nature of these phenomena is discussed in comparison with previous studies on C/S and C/I/S nanoheterostructures.

Original languageEnglish
Pages (from-to)144-151
Number of pages8
JournalJournal of Alloys and Compounds
Publication statusPublished - 30 Jun 2019

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    Ca, N. X., Hien, N. T., Tan, P. M., Phan, T. L., Thanh, L. D., Do, P. V., Bau, N. Q., Lien, V. T. K., & Van, H. T. (2019). Tunable dual emission in type-I/type-II CdSe/CdS/ZnSe nanocrystals. Journal of Alloys and Compounds, 791, 144-151. https://doi.org/10.1016/j.jallcom.2019.03.333