M. Barboza-Flores

Highly reproducible synthesis of hollow gold nanospheres with near infrared surface plasmon absorption using PVP as stabilizing agent

An improved synthetic method has been designed and demonstrated to reproducibly generate hollow gold nanospheres (HGNs) with strong surface plasmon resonance (SPR) absorption in the near infrared (NIR). The HGNs have been synthesized via galvanic replacement of cobalt with gold while utilizing different amounts of poly(vinylpyrrolidone) (PVP) as a template stabilizing agent. Ninety percent of syntheses performed by this modified method resulted in HGNs with an SPR near 800 nm, which is highly desirable for biomedical applications such as photothermal ablation (PTA) therapy, while other polymers (PAA and PEG) did not. Based on absorption and TEM measurements, PVP stabilizes the cobalt template particles via carbonyl-induced stabilization that slows nucleation and growth of the gold shell allowing for the generation of a reproducibly thin shell, thereby inducing a significant red shift of the SPR to 800 nm. The results are significant to various potential applications of HGNs, e.g. cancer therapy and sensing.

Monoclinic ZrO2 as a broad spectral response thermoluminescence UV dosemeter

Abstract The thermoluminescence characterization of polycrystalline monoclinic ZrO 2 samples prepared by the sol–gel process subjected to ultraviolet irradiation was performed. The results show that sol–gel synthesized ZrO 2 possesses good thermoluminescence efficiency as well as linear dose response. The thermoluminescence excitation spectrum covers the complete UVA, UVB and UVC range indicating a major advantage over other ultraviolet detector and dosemeters currently used.

Thermoluminescence and optically stimulated luminescence properties of nanocrystalline Er3+ and Yb3+ doped Y3Al5O12 exposed to β-rays

The thermoluminescence (TL) and optically stimulated luminescence (OSL) characterization of Er3+ and Yb3+ doped Y3Al5O12 nanocrystalline samples prepared by the precipitation process and exposed to β-rays are discussed. The TL as well as the OSL were two orders of magnitude higher in Er3+ doped than in Yb3+ specimens. The charge trapping and the radiative thermally stimulated recombination processes in Y3Al5O12 : Er3+ involve four trapping states at 166, 243, 342 and 424 °C, but just two trapping levels at 219 and 413 °C for Y3Al5O12 : Yb3+ at a heating rate of 10 °C s−1. The photostimulation with 470 nm light causes in both phosphors a radiative recombination of the optically free charge carriers belonging to the same trapping states. The TL and the OSL as a function of radiation dose behaviour were linear in the 10–100 Gy dose range. The results provide evidence of the potential uses of these materials in radiation storage and dosimeter devices.

Actinometric thermoluminescence response of KCl1−xBrx:Eu2+ mixed crystals

Europium‐doped KCl1−xBrx mixed crystals have been studied as a selective ultraviolet (UV) detector material in the actinometric region (200–300 nm). Thermoluminescence glow curves of room‐temperature UV‐irradiated samples were analyzed as a function of composition x and irradiation wavelength. A thermoluminescence enhancement, relative to the pure KCl and KBr end components is found; for 210–300 nm irradiation the KCl40Br60:Eu2+ solid solution presents a significant increase in thermoluminescence efficiency.

Thermally and optically stimulated luminescence correlated processes in X-ray irradiated KCl: Eu2+

Abstract The effect of optical bleaching on thermoluminescence (TL) and thermal bleaching on optically stimulated luminescence (OSL) outputs in X-ray irradiated KCl : Eu 2+ have been investigated. The X-ray induced glow curves reveal three main peaks located at 370, 410 and 470 K . Illumination with 560 nm light leads to a drastic change of the TL glow curve. The 470 K peak is destroyed during bleaching. The other peaks initially increase in intensity and only after sufficiently long bleaching begin to decrease. After long-time bleaching, the TL peaks in X-ray irradiated crystals look like the TL peaks found in UV irradiated crystals. The effect of thermal bleaching on OSL is also very pronounced. The temperature dependencies show a step-by-step decrease of the OSL intensity correlated with the positions of the TL peaks. The result obtained shows that centers responsible for the TL peaks participate in OSL, but this participation seems not to be direct and is complicated by processes accompanying the F center bleaching.

Thermoluminescence, Optical Stimulated Luminescence and Defect Creation in Europium Doped KCl and KBr Crystals

Europium doped alkali halide single crystals have been the subject of very intensive investigation due to its applications in digital medical radiography, optical memories and environmental dosimetry. The performance of these phosphorous materials exhibited in both thermoluminescence and optical stimulated luminescene, is generally explained through mechanisms where the photoionization of impurity is involved. However, no evidence of the presence of the Eu3+ ion has been reported yet. In this paper we present experimental insight into the defect creation processes generated by ionizing radiation, as well as ultraviolet light with energies below the band gap in both phenomena, which show the same 420 nm emission. The F and Fz centers are clearly related to the thermoluminescence glow curve. The results show a similar thermoluminescence and optical stimulated luminescence origin and may suggest the existence of a non-excitonic mechanism involved in the defect creation with ultraviolet non-ionizing radiation light.

Dosimetric characteristics of ultraviolet and x‐ray‐irradiated KBr:Eu2+ thermoluminescence crystals

Thermoluminescence (TL) characteristics of KBr:Eu2+ (150 ppm) previously exposed to ultraviolet (UV) light (200–300 nm) and x‐ray radiation at room temperature have been determined. The TL glow curve of UV‐irradiated samples is composed of six peaks located at 337, 384, 402, 435, 475, and 510 K. The TL glow curves of x‐irradiated samples show mainly a TL peak around 384 K. The TL intensities of UV‐irradiated (402 and 510 K glow peaks) and x‐irradiated specimens present a linear dependence as a function of radiation dose as well as fading stability 300 s after irradiation. These results further enhance the possibilities of using europium‐doped materials in nonionizing (actinic region) and ionizing radiation detection and dosimetry applications.

Thermoluminescence properties of aluminum oxide thin films obtained by pulsed laser deposition

Abstract The main thermoluminescence properties of amorphous aluminum oxide thin films prepared by pulsed laser deposition with thickness as low as 300 nm are presented. The obtained thin films were irradiated with UV (254 nm ) and beta-particle radiation ( 90 Sr - 90 Y ). Thermoluminescence glow curves exhibited two peaks centered at 95°C and 162°C for UV irradiation. For beta-particle irradiation the thermoluminescence glow curve shows only the presence of the high temperature peak. The 162°C peak shows good stability and 10% fading in the first 4 days after irradiation. A linear relationship between absorbed dose and the thermoluminescence response up to 20 Gy was observed for beta-particle irradiation. The thermoluminescence parameters obtained showed a second-order kinetics and an activation energy of 1.2 eV for the 162°C peak. These properties make aluminum oxide thin films potentially attractive as an ultra-thin dosimeter for UV and beta-particle radiation.

Room-temperature effects of UV radiation in KBr: crystals

Thermoluminescence and optical absorption measurements have been carried out in KBr: crystals irradiated with monochromatic UV light (200 - 300 nm) and x-rays at room temperature. For UV- and x-irradiated crystals strong similarities between the thermoluminescence glow curves have been found, suggesting that the low-energy UV radiation produces the same defects as produced by x-irradiation in this material. The thermoluminescence glow curves are composed of six glow peaks located at 337, 383, 403, 435, 475 and 509 K. Thermal annealing experiments in previously irradiated crystals show clearly a correlation between the glow peak located at 383 K and the F-centre thermal bleaching process. Also, the excitation spectrum for each thermoluminescence glow peak has been investigated, showing that the low-energy radiation induces the formation of F centres.

β-ray irradiation thermoluminescence and dosimetric characterization of KCl1−xBrx:Eu2+ mixed crystals

Abstract Thermoluminescence and dosimetric characterization of KCl 1− x Br x :Eu 2+ mixed crystals exposed to β -ray irradiation have been studied as a function of composition x in the mixed solid solution. Significant changes on its thermoluminescence properties and dosimetric behavior have been found concerning pure end KCl:Eu 2+ and KBr:Eu 2+ components. The results indicate a minimum thermoluminescence efficiency at about middle composition. The addition of small amount (1.0%) of Br − ion to KCl is more effective in producing a higher thermoluminescence efficiency and lower fading. It also enhances the linear response as a function of irradiation dose increasing greatly its application as an ionizing thermoluminescence dosimeter.