Development of Magnetic-Luminescent Bifunctional Nanomaterials and Their Application in Radiation Detection

Abstract

Bifunctional nanomaterials have exhibited potentially promising physico-chemical properties which can revolutionize and transform the landscape from bioclinical industry to next generation advance devices. In particular, colloidal nanoparticles have been extensively investigated as probes in biomedical and devices industries due to their unique size dependent electronic, optical, and magnetic properties amongst all possible building blocks of bifunctional materials. Superparamagentic ironoxide nanoparticles open up a new avenue to the development and application of photonic technologies such as novel optical devices and bioclinical research by coupling with fluorescent materials especialy rare eath ions. Rare earth nanomaterials, which feature long lived intermediate energy levels and intraconfigurational 4f-4f transitions, are promising supporters for photon conversion in a wide range of fluoride hosts covering UV to IR region and are preferred over other fluorescent materials due to their large stokes shift, sharp emission spectra, long lifetime, multiphoton and up/downconversion excitation-emission preocesses. Owing to the unusual magnetic and optical properties associated with f-electrons, rare-earth elements are very suitable for creating bifunctional materials themselves at platform of nanoscale by employing the unique magnetic and up/downconversion luminescence properties integrated within single particles upon proper choices of particle matrix and dopants. In the present thesis, we have discussed (i) bifunctionality of triply doped multicolor tuned photonic nanomaterials based on LaF3:Ce3+ ,Gd3+,Eu2/3+ prepared by polyol synthesis; (ii) green emitting triply doped bifunctional iron-oxide/ZnS@LaF3:Ce3+,Gd3+,Tb3+ nanocomposites with efficient optical and magnetic functionality, obtained using co-precipitation method; (iii) red/green emitting binary doped optical-magnetic up/downconverting β-NaGdF4:RE3+ and iron-oxide/SiO2/NaGdF4:RE3+ (RE= Ce, Eu; Yb, Er) nanoparticles using microwave assisted thermolysis; and (iv) scintillating response due to neutrons for colloidal nanoparticles of LaF3:Ce3+ ,Gd3+,Eu2/3+. The prepared materials have been well characterized structurally using powder x-ray diffraction, transmission elecron microscopy techniques and Fourier transform infrared spectroscopy. The excitation/emission (photoluminescence) investigations, time decay analysis of emitting level, and proposed energy transfer mechanism for different nanomaterials have been carried out and result in exciting optical characteristics due to f-f transition (Eu3+, Tb3+, Er3+) and f-d transitions (Ce3+, Eu2+) of rare earth ions. Furthermore, the magnetic characteristics of the materials were evaluated and materials containing iron-oxide as part of nanoentity displayed superparamgnetic nature whereas LaF3:RE3+ and NaGdF4:RE3+ showed their typical paramagnetic characteritcs at room temperature. Additionally, colloidal LaF3:Ce3+,Gd3+,Eu2/3+ nanoparticles proved to be efficient nanoscintillators for neutron detection, under irraditon of 241AmBe source. The result encouraged to test other nanomaterials under high energy irradiation and to further design of commercial nanoscintillators. The intense optical and sufficient magnetic peculiarities of the mentioned materials are probably quite appealing for magnetic-optical imaging (X-ray/γ-ray or NIR-Laser excitation), magnetic light-converting molecular devices and smart magnetic and radiationfield detection.