Krishnaprasad Sankar

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 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.

Scintillating-nanoparticle-induced enhancement of absorbed radiation dose

Cerium-doped lanthanum fluoride colloidal nanocrystals offer a way to improve external radiation therapy through the enhanced absorption of high energy photons, as well as through the emission of UV light in the presence of radiation, providing a second cell killing mechanism. Lanthanum fluoride nanocrystals doped with 10% cerium were anhydrously synthesized in methanol as platelets 10-12 nm in diameter and 4-6 nm thick. The nanocrystals were characterized by transmission electron microscopy, energy dispersive spectroscopy (EDS), and by steady state UV-visible optical absorption and photoluminescence spectroscopy. Using an incoming gamma flux from a 137Cs source and a Fricke dosimeter solution to measure absorbed energy, a 55% enhancement of absorbed dose was measured for a 1.2 mg/ml loading of nanocrystals over exposure range from one to four kiloroentgens.

Lanthanide-halide-based nanoscintillators for portable radiological detectors

Colloidal synthesis of core/shell nanocrystals with cerium-doped lanthanum fluoride core and undoped lanthanum fluoride shell, and of core/shell nanocrystals with hygroscopic cerium-doped lanthanum bromide core and undoped lanthanum fluoride shell is reported. The nanocrystals were characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS) analysis, steady state UV-VIS optical absorption and photoluminescence spectroscopy, and by photoluminescence lifetime measurements. Scintillation tests were performed on the cerium-doped lanthanum fluoride nanocrystalline material exposed to low-level gamma irradiation.

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)