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>Synthesis, Characterization, and Spectroscopy of Lanthanide-Doped Inorganic Nanocrystals; Radiant Flux and Absolute Quantum Yield Measurements of Upconversion Nanocrystals, and Fabrication of a Fiber-Optic Radiation Detector Utilizing Synthetically Optimized, Linearly Responsive Nanoscintillators.
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Synthesis, Characterization, and Spectroscopy of Lanthanide-Doped Inorganic Nanocrystals; Radiant Flux and Absolute Quantum Yield Measurements of Upconversion Nanocrystals, and Fabrication of a Fiber-Optic Radiation Detector Utilizing Synthetically Optimized, Linearly Responsive Nanoscintillators.
Presented herein is the laser power-dependent total radiant flux and absolute quantum yield measurements of homogeneous, solution-phase [NaYF 4; Yb (15%), Er (2%)] upconversion nanocrystals, and further compares the quantitative total radiant flux and absolute quantum yield measurements under both 970 nm continuous-wave and 976 nm pulsed Ti-Sapphire laser excitation (140 fs pulse-width, 80 MHz). This study demonstrates that at comparable excitation densities under continuous-wave and fs-pulsed excitation from 42 - 284 W/cm 2, the absolute quantum yield, and the total radiant flux per unit volume, are within a factor of two when spectra are integrated over the 500 - 700 nm wavelength regime. This study further establishes the radiant flux as the true unit of merit for quantifying emissive output intensity of upconverting nanocrystals for application purposes, especially given the high uncertainty in solution phase upconversion nanocrystal quantum yield measurements due to their low absorption cross-section. Additionally, a commercially available bulk [NaYF4; Yb (20%), Er (3%)] upconversion sample was measured in the solid-state to provide a total radiant flux and absolute quantum yield standard. The measurements were accomplished utilizing a custom-engineered, multi-detector integrating sphere measurement system that can measure spectral sample emission in Watts on a flux-calibrated (W/nm) CCD-spectrometer, enabling the direct measurement of the total radiant flux without need for an absorbance or quantum yield value.;Also presented is the development and characterization of a scintillating nanocrystalline composition, [Y2-xO3; Eux, Liy], in which Eu and Li dopant ion concentrations were systematically varied in order to define the most emissive compositions under specific x-ray excitation conditions. It is shown that these optimized [Y2-xO 3; Eux, Liy] compositions display scintillation responses that: (i) correlate linearly with incident radiation exposure at x-ray energies spanning from 40 - 220 kVp, and (ii) manifest no evidence of scintillation intensity saturation at the highest evaluated radiation exposures [up to 4 Roentgen per second].;The nanoscale [Y1.9O3; Eu0.1, Li 0.16] was further exploited as a detector material in a prototype fiber-optic radiation sensor. The scintillation intensity from a [Y1.9O 3; Eu0.1, Li0.16]-modified optical fiber tip, recorded using a CCD-photodetector or a Si-photodiode, was correlated with radiation exposure using a Precision XRAD 225Cx small-animal image guided radiation therapy (IGRT) system, an orthovoltage cabinet-irradiator, and a clinical X-ray Computed Tomography (CT) machine. For all x-ray energies tested from 80 - 225 kVp, this near-radiotransparent device recorded scintillation intensities that tracked linearly with total radiation exposure, highlighting its capability to provide alternately accurate dosimetry measurements for both diagnostic imaging and radiation therapy treatment. Because Si-based CCD and photodiode detectors manifest maximal sensitivities over the emission range of nanoscale [Y1.9O3; Eu0.1, Li 0.16], the timing speeds, sizes, and low power-consumption of these devices, coupled with the detection element's linear dependence of scintillation intensity with radiation dose, demonstrates the opportunity for next-generation radiation exposure measuring devices for in/ex vivo applications that are ultra-small, inexpensive, and accurate. (Abstract shortened by UMI.).
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