Academic literature on the topic 'Nanoscintillators'

A preliminary investigation of the scintillation response of rare earth-doped fluoride nanoparticles is reported. Nanoparticles of CaF2 : Eu, BaF2 : Ce, and LaF3 : Eu were produced by precipitation methods using ammonium di-n-octadecyldithiophosphate (ADDP) as a ligand that controls growth and lessens agglomeration. The structure and morphology were characterized by means of X-ray diffraction and transmission electron microscopy, while the scintillation properties of the nanoparticles were determined by means of X-ray and241Am irradiation. The unique aspect of scintillation of nanoparticles is related to the migration of carriers in the nanoscintillator. Our results showed that even nanoparticles as small as ~4 nm in size effectively scintillate, despite the diffusion length ofe-hpairs being considerably larger than the nanoparticles themselves, and suggest that nanoparticles can be used for radiation detection.

We explore the effect of shell thickness on the scintillation dynamics of CdS/CdSe/CdS spherical-quantum-well nanoscintillators under X-ray excitation, as compared to optical excitation at low and high powers.

To evaluate the efficiency of the photodynamic effect induced by X-rays, we quantified the fraction of energy deposited in nanoscintillators after interactions with X or γ-rays, introducing η_nano as a new loss parameter.

Radiation (RT) remains the most frequently used treatment against cancer. The main limitation of RT is its lack of specificity for cancer tissues and the limited maximum radiation dose that can be safely delivered without damaging the surrounding healthy tissues. A step forward in the development of better RT is achieved by coupling it with other treatments, such as photodynamic therapy (PDT). PDT is an anti-cancer therapy that relies on the light activation of non-toxic molecules—called photosensitizers—to generate ROS such as singlet oxygen. By conjugating photosensitizers to dense nanoscintillators in hybrid architectures, the PDT could be activated during RT, leading to cell death through an additional pathway with respect to the one activated by RT alone. Therefore, combining RT and PDT can lead to a synergistic enhancement of the overall efficacy of RT. However, the involvement of hybrids in combination with ionizing radiation is not trivial: the comprehension of the relationship among RT, scintillation emission of the nanoscintillator, and therapeutic effects of the locally excited photosensitizers is desirable to optimize the design of the hybrid nanoparticles for improved effects in radio-oncology. Here, we discuss the working principles of the PDT-activated RT methods, pointing out the guidelines for the development of effective coadjutants to be tested in clinics.

Abstract In this study, the scintillation properties of the (Lu1-x Y x )3Al5O12: 0.1 at.%Ce3+ mixed nanopowder scintillators synthesized by the sol-gel method were investigated. The light yield, energy resolution and scintillation decay kinetics for different substitutions of Lu3+ by Y3+ ion, namely 0 at.%, 5 at.%, 10 at.%, 15 at.% and 20 at.% were evaluated. The relative light yields of all LuYAG mixed samples were determined by the comparison method and the LuAG:0.1 at.%Ce3+ single crystal grown by the Czochralski technique was used as a reference detector. The scintillation decay kinetics was measured at the photomultiplier tube anode output and a fast digital oscilloscope was used to digitize signals. All measurements were performed under α-particles excitation from 241Am (E = 5.48 MeV) source to avoid light scattering in powder materials. Results show that the scintillation light yield was affected by the insertion of Y3+ ions in the LuAG host matrix and tends to improve in the range 10–20 at.% of Y3+ content. Furthermore, it was found that the main contribution in the energy resolution originates from the nanoscintillator material. The scintillation decay curves were well-fitted to a sum of three exponential functions, and the decay time constants were determined. Additionally, pulse shape discrimination of the mixed LuYAG nanoscintillators was also checked, and good discrimination of the kinetics measured under α-particles and γ-quanta from 137Cs (E = 662 keV) was observed.

I materiali luminescenti nanostrutturati sono largamente studiati per applicazioni in lampade e display, come scintillatori e nell’imaging biomedico. Pertanto, la ricerca nei nanomateriali prevede lo sviluppo di metodi di sintesi all’avanguardia per il controllo della loro struttura, morfologia e drogaggio. L’utilizzo di polveri nanocristalline per la fabbricazione di nanocompositi permette di ridurre l’incorrere di diverse problematiche come la diffusione della luce emessa; inoltre la dimensione nanometrica dei materiali è un requisito fondamentale per le applicazioni in biotecnologia, per la loro veicolazione attraverso il sangue e la penetrazione nelle cellule. Infine, la realizzazione di nanoparticelle (NP) aventi fase cristallina cubica permetterebbe la progettazione di ceramiche ottiche ad alta densità e quindi di una nuova classe di materiali luminescenti. L’ossido di afnio (HfO2) è stato considerato come fosforo di grande interesse grazie alle sue eccellenti proprietà chimiche e fisiche. In questo lavoro si sono investigate le proprietà di luminescenza e scintillazione di NP di HfO2 di diametro < 5 nm. Le NP pure e drogate con ioni di terre rare (TR) sono state fabbricate attraverso un processo di sintesi appositamente elaborato e ottimizzato. Il lavoro condotto ha permesso di controllare simultaneamente le proprietà strutturali e di luminescenza nelle NP. Particolare attenzione è stata rivolta al ruolo del drogaggio con ioni europio e lutezio tramite sintesi sol-gel non acquosa. L’analisi elementale, la caratterizzazione strutturale e morfologica con XRD, TEM/SEM, insieme alla spettroscopia vibrazionale Raman/IR, hanno confermato la trasformazione della fase cristallina da monoclina a cubica per concentrazioni > 5% mol di ioni Lu3+e Eu3+. Le proprietà ottiche sono state studiate attraverso tecniche di radio- e foto-luminescenza. I risultati ottenuti rappresentano un importante traguardo sia per una migliore comprensione della relazione struttura-proprietà di materiali di dimensione nanometrica, che per l’analisi della applicabilità di questi ultimi in campo tecnologico. In questo lavoro è stata dimostrata la possibilità di modificare lo spettro di emissione delle NP drogando simultaneamente con diverse TR e stabilizzando la fase cubica con l’incorporazione di ioni di Lu3+ otticamente inerte. L’HfO2 è un promettente materiale sia come matrice ospite per le TR che per la sua luminescenza intrinseca. NP non drogate sono state studiate considerando l’effetto della dimensione e della fase cristallina sulla luminescenza. Si è individuata la presenza di una banda di emissione composita nell’intervallo di lunghezze d’onda visibili, possibilmente correlata a difetti di superficie intrinseci o a impurezze del materiale. La sua intensità varia in funzione di trattamenti termici che portano alla modifica della superficie e del diametro delle NP, ed è confrontabile all’efficienza di materiali luminescenti commerciali usati come standard. In parallelo, sono state studiate le proprietà di NP luminescenti per applicazioni biologiche. Le nuove tecniche diagnostiche per immagini in vivo a fluorescenza con alta risoluzione e profondità di penetrazione si basano sulla luminescenza di NP nella finestra di trasparenza del tessuto biologico (1000-1400 nm). Inoltre, l’eccitazione a basse energie porta alla riduzione dell’autofluorescenza generata dai tessuti, componenti intra corporee e molecole organiche della dieta degli animali trattati con le NP. In questa ricerca, è stato dimostrato che l’utilizzo della banda a 1.3 m di ioni di Nd3+ in SrF2 permette di effettuare analisi di biodistribuzione e ottenere immagini in assenza di autofluorescenza e ad alto contrasto. La luminosità, la stabilità chimica e fisica così come l’elevata biocompatibilità rendono le NP di SrF2 promettenti per applicazioni biotecniche, bioimmagini a fluorescenza e future strategie diagnostiche.
Luminescent materials have found a wide variety of applications as phosphors for fluorescent lighting, display devices, X-ray monitoring and imaging, scintillators, and in biomedical imaging. The research on nanostructured materials resulted in the development of novel synthetic methods to control their structure, morphology, and doping. When the size of crystalline powders is tailored down to the nanoscale, several advantages are achieved, like the reduction of the emitted light scattering when fabricating optical nanocomposites. Nanoscale dimensions are also necessary in biotech applications where the material is required to travel in blood vessels and penetrate into cells. Finally, the realization of high density optical ceramics by nanoparticles (NPs) compaction can be pursued, especially with materials that possess cubic crystalline structure, leading to the bottom-up fabrication of a new class of luminescent materials. Hafnium oxide (HfO2) has gained interest in the last years as an attractive nanophosphor because of its excellent physical and chemical properties. In this work, the luminescence and scintillation properties of pure and rare-earth (RE) doped HfO2 NPs with a diameter < 5 nm have been investigated, obtained through a purposely designed synthetic strategy. This work was aimed at controlling the structural properties of NPs while optimizing their optical features. A particular attention has been paid to the role of doping with europium and lutetium ions through the non-aqueous sol-gel method. Structure and morphology characterization by XRD, TEM/SEM, elemental analyses, and Raman/IR vibrational spectroscopies have confirmed the occurrence of the HfO2 cubic polymorph for dopant concentrations larger than 5% mol for trivalent Lu3+ and Eu3+ ions. Optical properties have been investigated by radio- and photo-luminescence spectroscopy. Besides the relevance in application related issues, the results here reported represent an important dataset for a better comprehension of the structure-property relationship in materials confined into nanoscale dimensions. We also demonstrated the possibility of tuning the emission spectrum by multiple RE doping, while deputing the NP cubic structural stabilization to optically inert Lu3+ ions. Given the importance of HfO2 as host material for RE, its intrinsic optical response is also worth of investigation. Undoped HfO2 NPs were studied considering the effect of the size and of the crystal phase. A broad composite emission was observed in the visible range, potentially correlated both to intrinsic surface defects and to impurities. Its intensity can be varied by thermal treatments leading to surface modifications as well as to variations of particle dimensions. Its efficiency has been found to be comparable to that of standard commercial materials, evidencing the potential of pure HfO2 NPs as efficient phosphors. In parallel, we also investigated the use of emitting NPs for biological applications. Novel approaches for high contrast, deep tissue, in vivo fluorescence biomedical imaging are based on infrared-emitting NPs working in the so-called second biological window (1000 -1400 nm), where the partial transparency of tissues allows for the acquisition of high resolution, deep tissue images. In addition, the infrared excitation also leads to a reduction of auto-fluorescence generated by tissues, intra-body components, and specimen's diet. In my work, I exploited how the 1.3m emission band of Nd3+ ions embedded in SrF2 nanoparticles can be used to produce auto-fluorescence free, high contrast fluorescence images and bio-distribution studies. The strong brightness, the chemical and physical stability as well as high biocompatibility make Nd:SrF2 nanocrystals very promising infrared nanoprobes for in vivo imaging experiments in the second biological window.

Ce travail porte sur l'étude de nanoparticules scintillatrices qui sont capables, par définition, de convertir un rayonnement ionisant en lumière visible ou proche UV. Si le processus de scintillation est actuellement bien connu dans le cas des matériaux macroscopiques, les perturbations susceptibles d'apparaître pour des nanomatériaux le sont moins. En effet, des modifications peuvent être induites par le confinement spatial et les spécificités de structure propres aux nanomatériaux. L'étude de ces perturbations constitue l'objet de cette thèse. Le manuscrit se divise en trois parties. La première vise à quantifier la fraction d'énergie qui se dépose dans une assemblée de nanoparticules après interaction avec un photon haute énergie (X ) ou en réalisant des simulations Monte Carlo basées sur le code de calcul Geant4. La deuxième partie présente un travail expérimental exploratoire qui consiste à comparer des mesures de spectroscopie résolue en temps pour des nanoparticules et un monocristal afin d'extraire des informations sur les étapes de thermalisation et de recombinaison radiative spécifiques aux nanoparticules. La dernière partie de ce manuscrit présente l'étude d'une application novatrice des nanoscintillateurs comme agents thérapeutiques. Ils sont alors utilisés pour activer sous excitation X l'effet photodynamique, base d'une thérapie anti-cancéreuse actuellement limitée au traitement de lésions superficielles
This work deals with scintillating nanoparticles, material able to convert ionizing radiations into visible or Ultra-Violet light. The scintillation process is currently well-known for bulk materials. However, for nanomaterials, several steps of the scintillation process are likely to be slightly modified mainly because of the spatial confinement of charges and the structure specificities in nanomaterials. The study of such perturbations is the aim of this thesis. The manuscript is divided into three parts. The first one aims to quantify the amount of deposited energy within a set of nanoparticles after the interaction with a high energy photon (X or –rays). We thus developed Monte Carlo simulations with the Geant4 toolkit to quantify this energy. The second part presents an exploratory experimental study that consists in comparing time resolved spectroscopy measurements for nanoparticles and a single crystal. The aim is to extract a few tendencies on the thermalization and on the radiative recombination processes specific to nanoscintillators. The last part of this thesis presents an application of nanoscintillators as therapeutic agents. In that case, they are used to activate the photodynamic effect under X-ray irradiation. This last effect is the basis of the photodynamic therapy, an anticancer treatment currently limited to superficial tumors

The ability to interrogate structure-function photophysical properties on lanthanide-doped nanoscale materials will define their utility in next-generation applications and devices that capitalize on their size, light-conversion efficiencies, emissive wavelengths, syntheses, and environmental stabilities. The two main topics of this dissertation are (i) the interrogation of laser power-dependent quantum yield and total radiant flux metrics for a homogeneous, solution phase upconversion nanocrystal composition under both continuous wave and femtosecond-pulsed excitation utilizing a custom engineered absolute measurement system, and (ii) the synthesis, characterization, and power-dependent x-ray excited scintillation properties of [Y₂O₃; Eu] nanocrystals, and their integration into a fiber-optic radiation sensing device capable of in vivo dosimetry.

Presented herein is the laser power-dependent total radiant flux and absolute quantum yield measurements of homogeneous, solution-phase [NaYF₄; 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/cm2, 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, [Y_2-xO₃; Eu_x, Li_y], 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 [Y_2-xO₃; Eu_x, Li_y] 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]. X-ray excitation energies of 40, 120, and 220 kVp were chosen to probe the dependence of the integrated emission intensity upon x-ray exposure-rate in energy regimes where either the photoelectric or the Compton effect governs the scintillation mechanism on the most emissive [Y_2-xO₃; Eu_x, Li_y] composition, [Y_1.9O₃; Eu_0.1, Li_0.16]. These experiments demonstrate for nanoscale [Y_2-xO₃; Eu_x], that for comparable radiation exposures, when scintillation is governed by the photoelectric effect (120 kVp excitation), greater integrated emission intensities are recorded relative to excitation energies where the Compton effect regulates scintillation (220 kVp excitation).

The nanoscale [Y_1.9O₃; Eu_0.1, Li_0.16] was further exploited as a detector material in a prototype fiber-optic radiation sensor. The scintillation intensity from a [Y_1.9O₃; Eu_0.1, Li_0.16]-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 [Y_1.9O₃; Eu_0.1, 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.

Dissertation