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Photoluminescence response of colloidal quantum dots on VO2 film across metal to insulator transition.

Kuznetsov SN, Cheremisin AB, Stefanovich GB - Nanoscale Res Lett (2014)

Bottom Line: The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO2 across metal to insulator transition.Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition.It is a strong argument in favor of the proposed explanation based on the reflectance data. 71.30. + h; 73.21.La; 78.47.jd.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physico-Technical Department, Petrozavodsk State University, Lenin av. 33, 185910 Petrozavodsk, Russian Federation.

ABSTRACT

Unlabelled: We have proposed a method to probe metal to insulator transition in VO2 measuring photoluminescence response of colloidal quantum dots deposited on the VO2 film. In addition to linear luminescence intensity decrease with temperature that is well known for quantum dots, temperature ranges with enhanced photoluminescence changes have been found during phase transition in the oxide. Corresponding temperature derived from luminescence dependence on temperature closely correlates with that from resistance measurement during heating. The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO2 across metal to insulator transition. Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition. It is a strong argument in favor of the proposed explanation based on the reflectance data.

Pacs: 71.30. + h; 73.21.La; 78.47.jd.

No MeSH data available.


Related in: MedlinePlus

Relative reflectance response of VO2 film across metal to insulator transition. (a) Normalized reflectance at wavelength of 385 nm for heating and cooling (curves 1 and 2, respectively). (b) Corresponding derivatives (symbols) and their Gaussian fit (lines).
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Figure 5: Relative reflectance response of VO2 film across metal to insulator transition. (a) Normalized reflectance at wavelength of 385 nm for heating and cooling (curves 1 and 2, respectively). (b) Corresponding derivatives (symbols) and their Gaussian fit (lines).

Mentions: To clarify a mechanism of such behavior, first of all, we have examined purely the optical mechanism. In the PL measurements on our QDs, the two specific wavelength ranges are involved which are centered at 385 nm (excitation) and 630 nm (emission peak). Relative diffuse reflectance at both wavelengths is measured from the VO2 film without QDs when a temperature is crossing the MIT region. A reflectance was recorded by spectrophotometer equipped with an integrating sphere. It is revealed that there was no change in the reflectance at 630 nm (within approximately 1% accuracy). However, a noticeable change of approximately 10% in relative reflectance at 385 nm was observed under phase transition - see Figure 5a. It correlates with refractive index modulation in near-UV wavelength range across MIT [9]. Using a differentiation and Gaussian fitting for reflectance vs. temperature curves, characteristic parameters have been found. The results of this procedure are illustrated in Figure 5b for heating and cooling branches. In light of this finding, one may propose the following optical explanation for observed features in PL response of QDs atop the VO2 film. First, for our approximately 50-nm thick QD layer, nearly 50% of excitation intensity at 385 nm is absorbed under its forward propagation through this layer [10]. Second, if this QD layer is placed atop reflective surface (in our case VO2), a backscattered excitation light may be additionally absorbed by the QD layer. Obviously, it will lead to PL increase from QDs. Finally, when a temperature rises over MIT range, then the reflectance decreases (Figure 5a) and the PL intensity will decrease simultaneously (and vice versa under cooling).


Photoluminescence response of colloidal quantum dots on VO2 film across metal to insulator transition.

Kuznetsov SN, Cheremisin AB, Stefanovich GB - Nanoscale Res Lett (2014)

Relative reflectance response of VO2 film across metal to insulator transition. (a) Normalized reflectance at wavelength of 385 nm for heating and cooling (curves 1 and 2, respectively). (b) Corresponding derivatives (symbols) and their Gaussian fit (lines).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4232974&req=5

Figure 5: Relative reflectance response of VO2 film across metal to insulator transition. (a) Normalized reflectance at wavelength of 385 nm for heating and cooling (curves 1 and 2, respectively). (b) Corresponding derivatives (symbols) and their Gaussian fit (lines).
Mentions: To clarify a mechanism of such behavior, first of all, we have examined purely the optical mechanism. In the PL measurements on our QDs, the two specific wavelength ranges are involved which are centered at 385 nm (excitation) and 630 nm (emission peak). Relative diffuse reflectance at both wavelengths is measured from the VO2 film without QDs when a temperature is crossing the MIT region. A reflectance was recorded by spectrophotometer equipped with an integrating sphere. It is revealed that there was no change in the reflectance at 630 nm (within approximately 1% accuracy). However, a noticeable change of approximately 10% in relative reflectance at 385 nm was observed under phase transition - see Figure 5a. It correlates with refractive index modulation in near-UV wavelength range across MIT [9]. Using a differentiation and Gaussian fitting for reflectance vs. temperature curves, characteristic parameters have been found. The results of this procedure are illustrated in Figure 5b for heating and cooling branches. In light of this finding, one may propose the following optical explanation for observed features in PL response of QDs atop the VO2 film. First, for our approximately 50-nm thick QD layer, nearly 50% of excitation intensity at 385 nm is absorbed under its forward propagation through this layer [10]. Second, if this QD layer is placed atop reflective surface (in our case VO2), a backscattered excitation light may be additionally absorbed by the QD layer. Obviously, it will lead to PL increase from QDs. Finally, when a temperature rises over MIT range, then the reflectance decreases (Figure 5a) and the PL intensity will decrease simultaneously (and vice versa under cooling).

Bottom Line: The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO2 across metal to insulator transition.Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition.It is a strong argument in favor of the proposed explanation based on the reflectance data. 71.30. + h; 73.21.La; 78.47.jd.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physico-Technical Department, Petrozavodsk State University, Lenin av. 33, 185910 Petrozavodsk, Russian Federation.

ABSTRACT

Unlabelled: We have proposed a method to probe metal to insulator transition in VO2 measuring photoluminescence response of colloidal quantum dots deposited on the VO2 film. In addition to linear luminescence intensity decrease with temperature that is well known for quantum dots, temperature ranges with enhanced photoluminescence changes have been found during phase transition in the oxide. Corresponding temperature derived from luminescence dependence on temperature closely correlates with that from resistance measurement during heating. The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO2 across metal to insulator transition. Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition. It is a strong argument in favor of the proposed explanation based on the reflectance data.

Pacs: 71.30. + h; 73.21.La; 78.47.jd.

No MeSH data available.


Related in: MedlinePlus