This review summarizes recent progress in the design and applications of cadmium-free quantum dots (Cd-free QDs), with an emphasis on their role in biophotonics and nanomedicine. We first present the features of Cd-free QDs and describe the physics and emergent optical properties of various types of Cd-free QDs whose applications are discussed in subsequent sections. Selected specific QD systems are introduced, followed by the preparation of these Cd-free QDs in a form useful for biological applications, including recent advances in achieving high photoluminescence quantum yield (PL QY) and tunability of emission color. Next, we summarize biophotonic applications of Cd-free QDs in optical imaging, photoacoustic imaging, sensing, optical tracking, and photothermal therapy. Research advances in the use of Cd-free QDs for nanomedicine applications are discussed, including drug/gene delivery, protein/peptide delivery, image-guided surgery, diagnostics, and medical devices. The review then considers the pharma...

New Generation Cadmium-Free Quantum Dots for Biophotonics and Nanomedicine

In this study, both the linear and nonlinear intersubband optical absorption coefficients and the refractive index changes are calculated for the uniform, triangular and Gaussian-like donor distribution. The Gaussian-like distribution differs from the Gaussian distribution other authors use. The electronic structure of n-type Si δ-doped GaAs has been theoretically calculated by solving the Schrodinger and Poisson equations self-consistently. Our results show that the location and the size of the linear and total absorption coefficients and refractive index changes depend on the donor distribution type. The shape of δ-effective potential profile and the subband properties are changed as dependent on the donor distribution model. Therefore, the variation of the absorption coefficients and refraction index changes, which can be appropriate for various optical modulators and infrared optical device applications can be smooth obtained by the alteration donor distribution model.

Nonlinear intersubband absorption and refractive index change in n-type δ -doped GaAs for different donor distributions

In the present work, the case of a spherical quantum dot with parabolic confinement subjected to an external electric field with the presence of an impurity, the linear and third-order nonlinear optical absorption coefficients as well as refractive index changes have been calculated. The numerical method we are using for the calculation of the energy levels and the corresponding wave functions is the potential morphing method in the effective mass approximation. As our results indicate an increase of the electric field and/or the position of the impurity and/or the quantum dot radius redshifts the peak positions of the total absorption coefficient and total refractive index changes. Additionally, an increase of the position of the impurity and/or the quantum dot radius decreases the total absorption coefficient and increases the total refractive index changes. An increase also of the electric field decreases the total absorption coefficient but does not significantly affect the peak values of the total refractive index changes. Finally, an increase of the optical intensity considerably changes the total absorption coefficient as well as the total refractive index changes.

Linear and nonlinear optical absorption coefficients and refractive index changes in spherical quantum dots : Effects of impurities, electric field, size, and optical intensity

The electronic structure of a spherical quantum dot with parabolic confinement that contains a hydrogenic impurity and is subjected to a DC electric field is studied. In our calculations we vary the position of the impurity and the electric field strength. The calculated electronic structure is further used for determining the nonlinear optical rectification coefficient of the quantum dot structure. We show that both the position of the impurity and the strength of the electric field influence the nonlinear optical rectification process.

https://iopscience.iop.org/article/10.1088/0953-8984/19/39/395024/pdf

Electronic structure and nonlinear optical rectification in a quantum dot: effects of impurities and external electric field

We study the effects of excitons in nonlinear optical rectification in one-dimensional semiparabolic quantum dots. We consider the cases that the electron and the hole are confined in semiparabolic potentials (i) with the same oscillator frequency and (ii) with the same width. In the first case we present approximate analytical results in the strong confinement regime and find a closed-form relation between the nonlinear optical rectification coefficient of an exciton and the nonlinear optical rectification coefficient when only one electron exists in the structure. In the second case we use the Hartree-Fock approximation and the potential morphing method and present results for the nonlinear optical rectification coefficient in all confinement regimes.

Effects of excitons in nonlinear optical rectification in semiparabolic quantum dots

The linear and nonlinear intersubband optical absorptions 
in AlxlGa1-xlAs/GaAs/Alxr Ga1-xrAs asymmetric rectangular 
quantum well are studied within the framework of the density matrix 
formalism. We have calculated the electron energy levels and the envelope 
wave functions using the effective mass approach. In addition, we have 
obtained an expression for saturation intensity. It is shown that the 
parameters such as asymmetry and width of potential well not only shift the 
peak positions in absorption spectrum but also considerably modify their 
height. These results suggest that the absorption process can be easily 
controlled by the structure parameters of an asymmetric rectangular quantum 
well. Also, the incident optical intensity has a great effect on the total 
absorption spectrum. We have seen that the absorption peak is reduced by 
half when the optical intensity is approximately 0.8 MW/cm2 for well 
width L=90 A and β=0.5. Moreover, it is seen that the 
saturation intensity is quite sensitive to the structure parameters of an 
asymmetric rectangular quantum well. Thus, the results presented here can be 
useful for electro-optical modulators and photodetectors in the infrared 
region.

Linear and nonlinear intersubband optical absorptions in an asymmetric rectangular quantum well

In this work, both the intersubband optical absorption coefficients and the refractive index changes are calculated exactly in a quantum box. Analytical expressions for the linear and nonlinear intersubband absorption coefficients and refractive index changes are obtained by using the compact-density matrix approach. Numerical results are presented for typical GaAs/AlxGa1−x As quantum box system. The linear, third-order nonlinear and total absorption and refractive index changes are investigated as a function of the incident optical intensity and structure parameters such as box-edge length and stoichiometric ratio. Our results show that both the incident optical intensity and the structure parameters have a great effect on the total absorption and refractive index changes.

İbrahim Karabulut

Papers

Linear and nonlinear optical absorption coefficients and refractive index changes in spherical quantum dots : Effects of impurities, electric field, size, and optical intensity

Linear and nonlinear intersubband optical absorptions in an asymmetric rectangular quantum well

Linear and nonlinear intersubband optical absorption coefficients and refractive index changes in a quantum box with finite confining potential

Nonlinear optical rectification in asymmetrical semiparabolic quantum wells

Second and Third Harmonic Generation Susceptibilities of Spherical Quantum Dots: Effects of Impurities, Electric Field and Size