Tosifa A. Memon

Rapid degradation of CdSe/ZnS colloidal quantum dots exposed to gamma irradiation

Effects of Cs137 gamma irradiation on photoluminescent properties of CdSe∕ZnS colloidal quantum dots are reported. Optical degradation is evaluated by tracking the dependence of photoluminescence intensity on irradiation dose. CdSe∕ZnS quantum dots show poor radiation hardness, and severely degrade after less than 20kR exposure to 662keV gamma photons.

Synthesis and characterization of core/shell Fe3O4/ZnSe fluorescent magnetic nanoparticles

We report on the successful preparation and characterization of fluorescent magnetic core∕shell Fe(3)O(4)∕ZnSe nanoparticles (NPs) with a spherical shape by organometallic synthesis. The 7 nm core∕3 nm shell NPs show good magnetic and photoluminescence (PL) responses. The observed PL emission∕excitation spectra are shifted to shorter wavelengths, compared to a reference ZnSe NP sample. A dramatic reduction of PL quantum yield is also observed. The temperature dependence of the magnetization for the core∕shell NPs shows the characteristic features of two coexisting and interacting magnetic (Fe(3)O(4)) and nonmagnetic (ZnSe) phases. Compared to a reference Fe(3)O(4) NP sample, the room-temperature Néel relaxation time in core∕shell NPs is three times longer.

Synthesis and characterization of scintillating cerium-doped lanthanum fluoride nanocrystals

Colloidal synthesis of cerium-doped lanthanum fluoride nanocrystals is reported. The nanocrystals were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, steady-state UV-VIS optical absorption and photoluminescence (PL) spectroscopy, and by PL lifetime measurements. Cerium doping concentration was optimized for the maximum PL intensity. Radiation hardness of the synthesized nanocrystals was tested using a 137Cs 662-keV gamma source. Finally, scintillation was observed from the cerium-doped lanthanum fluoride nanocrystals exposed to low-level gamma radiation.

Nanophosphors based on CdSe/ZnS colloidal quantum dots for daylight-quality white LEDs

Properly mixed combination of CdSe/ZnS colloidal quantum dots of different sizes is suggested as a nanophosphor material to be combined with blue InGaN/GaN LEDs for well-balanced color content of white light emission.

Fast-decay-time scintillation of LaF 3 :Ce colloidal nanocrystals

Positron emission tomography requires high-brightness fast-decay scintillators for coincidence counting of positron annihilation events. We demonstrate that LaF3:Ce nanocrystals show promising characteristics for that application. Scintillation response and photoluminescence lifetime below 27 ns are measured.

Effects of gamma irradiation on optical properties of CdSe/ZnS colloidal quantum dots

Effects of 137Cs gamma irradiation on photoluminescent properties of CdSe/ZnS colloidal quantum dots are reported. Optical degradation was evaluated by measuring dependence of photoluminescence intensity on irradiation dose. CdSe/ZnS quantum dots show poor radiation hardness.

Synthesis and characterization of scintillating lead-iodide-based nanocrystals

Lead-iodide-based nanocrystals were synthesized by dissolution of commercial lead iodide powder in a coordinating solvent, tetrahydrofuran, and subsequent re-crystallization after an optimum addition of methanol. The nanocrystals were characterized by transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy (EDS), steady state UV-visible optical absorption and photoluminescence spectroscopy, and by photoluminescence lifetime and quantum efficiency measurements. The radiation hardness of the synthesized material was tested using a 137Cs gamma source. Scintillation was observed from the lead-iodide based material exposed to low-level gamma irradiation.

Effects of Gamma Irradiation on Optical Properties of Colloidal Nanocrystals

The effects of {sup 137}Cs gamma irradiation on photoluminescence properties, such as spectra, light output, and lifetime, of several types of colloidal nano-crystals have been investigated. Irradiation-induced damage testing was performed on CdSe/ZnS, LaF{sub 3}:Eu, LaF{sub 3}:Ce, ZnO, and PbI{sub 2} nano-crystals synthesized on a Schlenk line using appropriate solvents and precursors. Optical degradation of the nano-crystals was evaluated based on the measured dependence of their photoluminescence intensity on the irradiation dose. Radiation hardness varies significantly between various nano-crystalline material systems. (authors)