Ilya Weinstein
Ural Federal University, NANOTECH Centre
Ilya Weinstein is a Professor at Ural Federal University, Ekaterinburg. He did his PhD in Ural State Technical University at 1997 and then during 2002 – 2004 served as vice-dean of Physics & Technology Faculty. At that time his main scientific interests were in properties investigation of luminescent materials for solid state dosimetry. In 2009 just after Dr.Sc. Degree I. Weinstein became Head of the newly organized NANOTECH Centre in UrFU. Currently his group researches are focused on synthesis and study of new nanostructured luminophores for photonics applications.
Colloidal core/shell quantum dots (QD) based on non-toxic indium phosphide surrounded by more widegap zinc sulphide are being extensively investigated [1]. At the same time, the effect of temperature on the optical properties of InP/ZnS nanocrystals remains insufficiently studied both from the standpoint of experimental analysis and consistent theoretical justifications [2]. This work aims to investigate temperature behavior of optical absorption (OA) and photoluminescence (PL) spectra of InP/ZnS QD in the range of 6.5-296 К.
Two colloidal samples of 2.1 nm (QD-1) and 2.3 nm (QD-2) average sizes capped with modified polyacrylic acid (Research Institute of Applied Acoustics, Dubna) were studied. Control, change and monitoring of temperature were carried out by means of a CCS-100/204N model Janis closed cycle refrigerator system and Model 335 controller. OA spectra were measured using the module integrated in Shimadzu UV-2450 spectrophotometer. To detect PL response under UV LED excitation the module was coupled with Andor Technology Shamrock SR-303i-B spectrograph and NewtonEMDU-970P-BV-602 CCD-camera.
The OA spectra at 296 K feature the first exciton absorption bands of InP with the energies of 2.60 (QD-1) and 2.38 (QD-2) eV determined by the second-order derivative technique. Blueshift of the bands upon cooling is analyzed by virtue of the formalism assuming efficient exciton-phonon interaction. FWHM of the first exciton absorption band are found to be temperature-independent (Fig.1). Numerical simulation shows that FWHM of resulting band for the dots ensemble does not vary with temperature changes of Gaussian spectral components (shift, broadening, area) for the individual nanocrystals allowing for its distributions in size, shape etc. The calculated model parameters are analyzed based on comparison with independent data for bulk crystals and QDs. It is observed that PL spectra represents asymmetrical bands at 2.32 (QD-1) and 2.14 (QD-2) eV. Intensity of the exciton PL bands increases by a factor of 7 when cooled. Simultaneously the spectra reveal hidden components which intensity rises more than 15 times (Fig.2). Mechanisms of the observed luminescence and band broadening effects in the InP/ZnS quantum dots are discussed.
[1] S.S.Savchenko, A.S.Vokhmintsev, I.A.Weinstein, J.Phys.:Conf.Series, 741, 012151 (2016).
[2] S.S.Savchenko, A.S.Vokhmintsev, I.A.Weinstein, Opt.Mater.Express, 7, 354 (2017).
Optical properties of nanostructures , Quantum dots and colour centres