Thermoluminescence and defect centers in synthetic diopside

MgCaSi2O6 polycrystal was synthesized by the devitrification method. The dosimetric characteristics by TL of this prepared polycrystal was investigated. This material exhibits TL peaks at 115, 160, 210, 260 and 280 °C. The dosimetric peak occurs at 260 °C with a well defined glow curve structure. This peak shows a linear dose response. Electron paramagnetic resonance (EPR) studies have been carried out to identify the defect centers responsible for the TL peaks. Two defect centers in the region of g = 2.0 are found. One of the centers (center I) with a g factor equal to 2.0085 is identified as O− -ion and relates with the observed high temperature 250 and 300 °C TL peaks. Additional defect centers with g = 2.0012 (center II) and 1.982 (center III) are due to F+- centers (electron trapped at an oxygen vacancy). Center II and III correlate with the TL peaks at 160 °C and 106 °C, respectively.Campus Arequip

Improvement in the Environmental Stability of Tris(8-hydroxyquinoline) Aluminum by Substitution of Sulphonic Acid in 8-hydroxyquinoline Ligand

Tris (8-hydroxyquinoline) aluminum (Alq3) is a commonly used electron transporting and/or light emitting material in organic light emitting diodes (OLEDs). However, it is well known that Alq3 is very sensitive to atmosphere exposure and that photoluminescence of Alq3 films decreases with the time of atmosphere exposure. Degradation is also a serious problem in Alq3 based OLEDs. Several degradation mechanisms have been identified in these devices, including formation of unstable cationic species due to passage of holes. Therefore, there is lots of interest in improving the stability of Alq3. We have synthesized Tris (8-hydroxyquinoline-5 sulphonic acid) aluminum [Al(qS)3] in order to improve the stability. We performed electron spin resonance measurements on Alq3 and Al(qS)3 powders. Unlike Alq3 which exhibited strong ESR signal, Al(qS)3 produced no detectable ESR signal indicating absence of free radicals in this material. To test the environmental stability of Al(qS)3 films, we have performed photoluminescence (PL) measurements in humid air at different temperatures and found that Al(qS)3 exhibits improved stability. After comparing the stability of Alq3 and Al(qS)3 thin films, fabrication of the light emitting diodes with Al(qS)3 emitting layer was attempted in order to compare the performance with Alq3 based devices

Dating stalagmite from Caverna do Diabo (Devil´S Cave) by TL and EPR techniques

ABSTRACT A cylindrical fragment of stalagmite from Caverna do Diabo, State of São Paulo, Brazil, has been studied and dated by thermoluminescence and electron paramagnetic resonance techniques. The thermoluminescence glow curves of stalagmite samples and subsequently gamma irradiated, have shown rise of three peaks at 135, 180 and 265 °C. From electron paramagnetic resonance spectra of stalagmite was possible to clearly identify three paramagnetic centers in the g = 2.0 region: Centers I, II and III are due to , and , respectively. The additive method was applied to calculate the accumulated dose using thermoluminescence peak at 265 °C and the electron paramagnetic resonance signal at g = 1.9973 of CO- 2 radical. The ages of the different slices of stalagmite were determined from the Dac- values and Dan- value, obtaining an average of 86410 for central slice, 53421 for second slice, 31490 for third slice and 46390 years B.P. for the central region of upper end