Temperature dependence of absorption band edge of CdTe nanocrystals in glass

Allahverdi, Ç.; Yükselici, M. H.

doi:10.1088/1367-2630/10/10/103029

Cited by 17 publications

(14 citation statements)

References 15 publications

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“…The data from this low-nanocrystal-concentration region of the dried drop are consistent with a temperature increase of at most 10 K above room temperature [41,42]. This is in fact the maximal expected thermal effect of a focused laser for the powers and spot size used in our experiments, given dissipation through contact with the Si 3 N 4 substrate which we suppose remains at room temperature for regions more than 5 μm away from the laser spot.…”

Section: Resultssupporting

confidence: 83%

Characterization of the Dynamics of Photoluminescence Degradation in Aqueous CdTe/CdS Core-Shell Quantum Dots

Assis

et al. 2015

J Fluoresc

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We investigate the effects of the excitation power on the photoluminescence spectra of aqueous CdTe/CdS core-shell quantum dots. We have focused our efforts on nanoparticles that are drop-cast on a silicon nitride substrate and dried out. Under such conditions, the emission intensity of these nanocrystals decreases exponentially and the emission center wavelength shifts with the time under laser excitation, displaying a behavior that depends on the excitation power. In the low-power regime a blueshift occurs, which we attribute to photo-oxidation of the quantum dot core. The blueshift can be suppressed by performing the measurements in a nitrogen atmosphere. Under high-power excitation the nanoparticles thermally expand and aggregate, and a transition to a redshift regime is then observed in the photoluminescence spectra. No spectral changes are observed for nanocrystals dispersed in the solvent. Our results show a procedure that can be used to determine the optimal conditions for the use of a given set of colloidal quantum dots as light emitters for photonic crystal optical cavities.

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Section: Resultssupporting

confidence: 83%

Characterization of the Dynamics of Photoluminescence Degradation in Aqueous CdTe/CdS Core-Shell Quantum Dots

Assis

et al. 2015

J Fluoresc

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“…It is known that the temperature dependence of the energy gap of bulk semiconductor crystals is described by the empirical Varshni equation:

E_{g} = E_{o} - α \frac{T^{2}}{T + θ}

where E 0 is the energy gap at 0 K, θ is the Debye temperature (for bulk CdTe θ = 160 K) and α is the temperature sensitivity. In previous studies , the Varshni equation has been used to describe the temperature dependence of the energy gap of QDs. We assume that the energy dependence of the PL of semiconductor nanoparticles has a similar relationship, and therefore the temperature sensitivity of QDs of certain size can be determined from the slope of the linear approximation plotted in the coordinates E PL vs αT 2 /( T + θ).…”

Section: Resultsmentioning

confidence: 99%

“…In Allahverdi et al , the difference between the sensitivity of bulk and nanosized semiconductor crystals is explained in terms of the influence of quantum confinement, a change in the electron–phonon interaction, and the influence of thermal strain. Thus, the temperature sensitivity of the nanoscale crystal ( α nano ) can be expressed as:

α_{italicnano} = α_{italicbulk} + 2 k_{B} (S_{italicnano} - S_{italicbulk}) + \frac{h^{2} π^{2}}{μ R_{italicave}^{2}} β + (\frac{\partial E_{g}}{\partial P}) [3 B_{0} (β_{H_{2} O} - β)]

where α bulk is the temperature coefficient of bulk semiconductor, S nano , S bulk is the Huang–Rhys factors for nanoscale and bulk semiconductor respectively, k B is the Boltzmann constant, R ave is the average radius of nanoparticles, μ is the reduced mass of the electron and hole, h is the Planck's constant, β is the average temperature expansion coefficient of nanocrystals,

((), \frac{\partial E_{g}}{\partial P})

is a change in the energy gap due to changes in lattice pressure, B 0 is the bulk modulus and

β_{H_{2} O}

is the coefficient of thermal expansion of the environment (which is water in our case).…”

Section: Resultsmentioning

confidence: 99%

Size‐dependent temperature sensitivity of photoluminescence peak position of CdTe quantum dots

Vyhnan

Khalavka

2013

Luminescence

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The size dependence of the temperature coefficient (sensitivity) of the photoluminescence (PL) peak position of CdTe quantum dots stabilized by thioglycolic acid in aqueous solution has been investigated. Temperature sensitivity increases as the average radius of CdTe quantum dots decreases. This must be taken into account in the design of solar light concentrators and light-emmiting diode-monitors as well as other technologies in which a fine tuning of the light emission is important.

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“…Strain, due to dangling bonds at the interfaces and surfaces, and quantum size effects, due to the charge confinement in the nanometer‐scale structure of films, might both lead to this redshift in the bandgap energy ( E R ) of the film. The average radii or grain sizes ( R ave ) are evaluated by using size‐dependent bandgap energy of the film ( E R ) :

E_{R} true(eV true) = E_{g} true(eV true) - \frac{0.14}{R_{ave} true(n m true)} + \frac{0.376}{μ {[R_{ave} (normaln normalm)]}^{2}} + Δ E_{strain},

where E g is the bandgap energy of the bulk and it is given by the value E g = 1.44 eV , μ is the reduced mass of an electron–hole pair in units of electron rest mass ( m 0 ) , and it is given by μ = 0.08 (in m 0 units) . Δ E strain is the energy due to the strain and it was estimated at about 2.2% of the 710 meV total redshift that takes place in the absorption edge energy with increasing film thickness from 100 to 500 nm.…”

Section: Modelingmentioning

confidence: 99%

“…where E g is the bandgap energy of the bulk and it is given by the value E g ¼ 1.44 eV [30], m is the reduced mass of an electronhole pair in units of electron rest mass (m 0 ) [31], and it is given by m¼ 0.08 (in m 0 units) [32]. DE strain is the energy due to the strain and it was estimated at about 2.2% of the 710 meV total redshift that takes place in the absorption edge energy with increasing film thickness from 100 to 500 nm.…”

mentioning

confidence: 99%

Structural and optical properties of CdTe thin film: A detailed investigation using optical absorption, XRD, and Raman spectroscopies

Nassar

Yükselici

Bozkurt

2016

Physica Status Solidi (b)

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Physical vapor deposition (PVD) is used to grow CdTe thin films of different thicknesses on glass substrates. The characterization of the samples is then investigated optically and structurally. Three experimental techniques were used in this study; optical absorption (ABS), Raman, and X‐ray diffraction (XRD) spectroscopies. In optical ABS spectroscopy, the Urbach energy related to the width of long‐wavelength tail decreases from 827 to 585 meV as the thickness increases from 100 to 500 nm, respectively. The thickness‐dependent particle size was calculated using the value of the size‐dependent optical absorption edge energy. A shift of 710 meV in the ABS edge energy takes place as the thickness increases from 100 to 500 nm. Thickness‐dependent shifting and widening of XRD line is presumably due to the size effect and strain. Relative to the phonon frequency of bulk CdTe crystal, a thickness‐dependent blueshift was observed in Raman spectra for the Longitudinal Optical (LO) phonon frequency, while a redshift for the longitudinal acoustic (LA) and transverse optical (TO) phonon frequencies is observed. In the present work, the results of optical absorption, XRD, and Raman analyses are combined in order to study the effect of particle‐size evolution, thickness‐dependent strain, and structural disorder.

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Temperature dependence of absorption band edge of CdTe nanocrystals in glass

Cited by 17 publications

References 15 publications

Characterization of the Dynamics of Photoluminescence Degradation in Aqueous CdTe/CdS Core-Shell Quantum Dots

Characterization of the Dynamics of Photoluminescence Degradation in Aqueous CdTe/CdS Core-Shell Quantum Dots

Size‐dependent temperature sensitivity of photoluminescence peak position of CdTe quantum dots

Structural and optical properties of CdTe thin film: A detailed investigation using optical absorption, XRD, and Raman spectroscopies

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