Structure–property correlations in oxyfluoride glasses have been explored in a series of lead fluoroborate and lead fluorogermanate glasses with nominal compositions (50 – x – y – z)B2O3–40PbO–y(Al2O3)–(10 + x)PbF2–zREF3 and (50 – x – y)GeO2–40PbO–y(Al2O3)–(10 + x)PbF2–zREF3 (x, y = 0, 10, 0 ≤ z ≤ 0.5, RE = Eu, Yb). Starting from glasses with a fixed PbF2 content of 10 mol %, we explore the effects of (1) increasing PbF2 content to 20 mol % and (2) incorporating the intermediate oxide Al2O3 at the expense of GeO2 or B2O3. The emission characteristics studied on Eu-doped glasses are rationalized on the basis of structural information obtained by Raman, nuclear magnetic resonance (NMR), and pulsed electron paramagnetic resonance (EPR) spectroscopies on Yb-doped samples. In the Ge-oxyfluoride glasses, increasing PbF2 content results in enhanced excited-state lifetimes of the rare-earth ions, and for this system, Eu3+ emission profiles, NMR, and EPR results suggest an increased average number of fluoride ions in the first coordination sphere of the rare-earth ions. In contrast, the effect is much less apparent in the fluoroborate glasses. In both systems, Al2O3 incorporation results in pronounced changes in the fluorine speciation, indicating the formation of aluminum–fluorine bonds.
ResumenEn este trabajo se presentan los resultados obtenidos al datar por medio de resonancia paramagnética electrónica (RPE) muestras de esmalte dental humano provenientes del sitio arqueológico de Checua, situado a 5º 04' de latitud norte y a 73° 53' de longitud este, a una altitud de 3.600 m sobre el nivel del mar, y a 60 km al noreste de Bogotá. El esmalte dental se irradió con rayos gama y los radicales libres producidos se cuantificaron usando un espectrómetro de RPE, banda X. A partir de la curva de intensidad de la señal RPE, comparada con la dosis absorbida por el esmalte, se hizo un ajuste que permitió obtener la dosis media arqueológica acumulada en el esmalte (D E ) durante el periodo de enterramiento de la muestra. El valor obtenido fue de 3,0 ± 0,08 Gy. Para estimar la edad de la muestra se usó el programa computacional ROSY, obteniendo una edad media del individuo de 5.021 ± 202 años antes del presente. La edad de las muestras corresponde a seres humanos que vivieron en el periodo cuaternario, en la época del holoceno. Los resultados obtenidos muestran el potencial de la técnica RPE como herramienta de datación de muestras cuaternarias en Colombia y abre la posibilidad de usarla en otro tipo de muestras como estalagmitas, calcitas, conchas de moluscos y corales. Este trabajo es el tercero realizado en Colombia en este campo después del trabajo de tesis de Sandoval y Carvajal (Sandoval 2010, Carvajal 2011 a,b).Palabras clave: EPR, esmalte dental, datación arqueológica. Electron paramagnetic resonance dating of archaeological rests from Checua (Cundinamarca -Colombia) AbstractThis paper presents the results obtained from using electron paramagnetic resonance (EPR) to analyse human tooth enamel found at the Checua archaeological site (Cundinamarca, Colombia), located 5º 04' latitude north and 73° 53' longitude east, 3,600 m above sea level and 60 km northeast of Bogotá. The tooth enamel was irradiated with gamma rays and the resulting free radicals were measured using an electron spin resonance (ESR) X-band spectrometer. Comparing the RPE signal intensity curve to the absorbed dose, it was possible to adjust this curve, which allowed us to obtain the mean archaeological dose accumulated in the enamel (D E ) during the period it was buried. The resulting value was 3.20 ± 0.08 Gy. By using the ROSY software, the mean age was estimated at 5021 ± 202 years before present (BP). This age corresponds to human beings who lived in the Quaternary period, Holocene epoch. These results show the EPR technique potential as a tool for dating Quaternary samples in Colombia and open the possibility of using it in stalagmite, calcite, mollusc shell and coral reef samples. This study is the third conducted in Colombia after the thesis work by Carvajal and Sandoval (Sandoval, 2010, Carvajal, 2011.Key words: EPR/ESR, tooth enamel, Colombia, archaeological dating. IntroducciónEl hombre siempre ha mostrado gran interés por su origen y su desarrollo a través de los tiempos, preguntándose sobre el qué, el cómo, el dónde y el...
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