Luminescence of α-Al2O3 and α-AlOOH natural mixtures (original) (raw)
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Luminescence of -Al 2 O 3 and -AlOOH natural mixtures
Natural mixtures of sapphire ( -Al2O3) and diaspore ( -AlOOH) samples from Goian (NW Spain) have been analysed by scanning electron microscopy, electron microprobe, spectral luminescent techniques (thermoluminescence, radioluminescence, cathodoluminescence) and inductively coupled atomic plasma bulk analyses. Blue coloured areas could be attributed to chromophore elements (FeO = 0:278%, TiO2 = 0:023%) and the large photon emission peak observed at 700 nm with 80 ppm of Cr2O3. Additional smaller bands at 670 and 720 nm can be assigned to Ti 4+ and FeO in the lattice. The coexistence of two di erent types of luminescent behaviour in the lattice of this material, such as a discrete electron trap distribution at lower temperature (circa 190 • C) and a continuous trap structure at higher temperature (over 250 • C) and their relationship with dehydroxylation and chromophore oxidation are explored.
Applied Radiation and Isotopes, 2012
This paper reports on the Thermoluminescence (TL) and Cathodoluminescence (CL) emission of wellcharacterized hydrothermal milky quartz specimens from Hakkari in Turkey, labeled THQ, and Madrid in Spain, labeled SHQ, and metamorphic quartz from Madrid, in Spain, labeled SMQ. Both hydrothermal and metamorphic quartz samples display similar UV-IR CL spectra consisting of five groups of components centered at 330 nm and 380 nm linked to [AlO 4 ]1 centers, 420 nm due to intrinsic defects such as oxygen vacancies, lattice defects, and impurities which modify the crystal structure, 480 nm associated with [AlO 4 ]1 centers of substitutional Al 3 þ , and a red broad band related to the hydroxyl defects in the quartz lattice as precursors of non-bridging oxygen hole centers (NBOHC) and substitutional point defects. The Turkish quartz specimen exhibits higher CL intensity in the UV region (up to 330 nm) than the Spanish specimens probably linked to the presence of Ca (0.95% in THQ and less than 0.1% in SHQ and SMQ). At wavelengths greater than 330 nm, SMQ (formed at high pressure 6000 bars and temperatures over 500-600 1C) shows higher intensity than the hydrothermal (growth at 2000 bars and temperatures 200-300 1C) samples associated with the formation process. The natural blue TL glow curves of both THQ and SHQ display a weaker TL intensity than the SMQ, attributable to the Al (0.32%), Ti (0.14%), K (0.01%) and Zr (76 ppm) content. It is shown that mineralogical formation, crystallinity index and the content of the impurities seem to be the main parameters of influence in the shape intensity of the CL and TL glow curve emission.
Study of the thermoluminescence emission of a natural α-cristobalite†
Radiation Effects and Defects in Solids, 2009
The thermoluminescence (TL) properties of a well-characterised natural α-cristobalite from Lanzarote (Canary Islands, Spain) have been studied. The natural blue emission (at 400 nm) of this silica polymorph of quartz reveals the appearance of three groups of components peaked at 150, 230-240 and 370 • C, which could be associated, respectively, with (i) structural defects (similar to quartz), (ii) the reversible phase transition from α-cristobalite to β-cristobalite and (iii) electron recombination with unstable holes trapped at oxygen vacancies next to Al ions linked to the formation of β-cristobalite. Similar to quartz, the induced TL (ITL) glow curves display four maxima, peaked at 90, 110, 180 and 220 • C, which could be respectively associated with (i) oxygen vacancies, (ii) recombination of electrons with (H 3 O 4 ) • centres that can act as hole traps, (iii) [GeO 4 ] − centres that are stabilised with monovalent cations (H + , Li + or Na + ) and (iv) [AlO 4 ] • hole-like centres that are created when alkali ions are moving away from Al sites related probably to the reversible phase transition. The dose dependence of the ITL emission of β-irradiated samples at room temperature exhibits a linear increase in the glow intensity of the 180 • C maximum when increasing the dose (r = 0.997) in the range 0.5-10 Gy.
Effect of the chemical impurities on the luminescence emission of natural apatites
We report the cathodoluminescence and blue thermoluminescence of natural apatites. We characterized the samples by X-ray diffraction and Raman spectroscopy. The apatites show CL wavebands linked to Ce 3+ , Tb 3+ , Dy 3+ , Sm 3+ , Pr 3+ , Mn 2+ and UO 2þ 2 . All the studied aliquots exhibit one single UV-blue TL peak at 370, 256 and 268°C. The crystallinity index are related with the different compositions of the apatites.
Visible Luminescence of Colour Centres in Sapphire
physica status solidi (b), 1984
The colour centres introduced in sapphire crystals by neutron irradiation and by thermochemical treatment exhibit polarized luminescence. In neutron-irradiated crystals an absorption band at 4.1 eV and luminescence bands at 2.45 and 3.8 eV are due to one type of centres, most probably interstitial aluminium ions. Other donor-type centres give rise t o an absorption band at 2.75 eV and a luminescence band at 2.2 eV. In magnesium containing crystals similar centres absorbing a t 2.93 eV and emitting a t 2.35 eV can be introduced by thermochemical treatment in reducing atmosphere. The preliminary study of the red luminescence indicates its connection with the absorption bands a t 3.45 and 3.8 eV.
Analysis of luminescence spectra of leucite (KAISiO4)
The Analyst, 2001
High-sensitivity radioluminescence (RL) and thermoluminescence (TL) measurements were carried out on samples of natural leucite (with 2.95% of Na 2 O) from Campania Vessa (Italy). Samples were annealed to modify the charge compensation through alkali metal self-diffusion and to produce luminescence centres. High-temperature powder diffraction, scanning electron microscopy and chemical analyses were performed to monitor the tetragonal-cubic phase transitions and the thermal drainage of alkali metal ions from the aluminosilicate lattice. The emission spectral bands of leucite (300, 380, 430, 480, 560 and 680 nm) match those of other Na/K-aluminosilicates (alkali metal feldspars) and could be attributed to similar defects. TL glow curves of increasingly pre-irradiated natural leucite (range 0-20 Gy) showed no changes above 300 °C, whereas some changes were observed with annealed samples (1000 °C for 12 h). This temperature is the starting point of Na self-diffusion within the aluminosilicate lattices. The areas of the TL glow curves of both natural and annealed b-irradiated leucites can be fitted with a linear function with high correlation. These results are in agreement with high alkali metal loss (K 2 O ~12% and Na 2 O ~18%) during thermal pre-treatment, high cell volume expansion (from 2350 to 2500 Å) and the cubic Ia3d " tetragonal I4 1 /a phase transition. This promotes the egress of alkali metal ions and the production of [AlO 4 /M + ]°, [AlO 4 /H + ]° and [AlO 4 ]° luminescence centres.
Radioluminescence of synthetic quartz related to alkali ions
Journal of Luminescence, 2012
The radioluminescence (RL) of synthetic quartzes (GEMMA Quartz & Crystal Company) has been measured at room temperature. Some samples were treated by electrodiffusion (''sweeping'') in order to change the concentrations of alkali ions, mainly Li þ and Na þ , which in quartz are known to be linked to Al ions, substitutional for Si ions. The RL emission spectra show evidence of a role of alkali ions in affecting some specific emissions. All the spectra could be analysed as composed of four bands in the blue and UV region. Specifically, the well known blue emission at around 470 nm was seen to be composed by two bands at 430 nm (2.86 eV) and at 485 nm (2.53 eV). Effects of irradiation, during the RL measurements, were clearly seen only in the ''Li swept in'' sample, namely an increase in the 485 nm band intensity and a decrease in the 430 nm band one. The previously reported UV emission was detected at 355 nm (3.44 eV) in all the samples, being the most intense band in the ''swept out'' sample. A further UV emission was detected at 315 nm (3.94 eV), more intense in untreated samples. Possible assignments of the detected emission bands are discussed in relation to the defects of quartz, specifically focusing on the Al centres that are most affected by sweeping procedures.
Sapphire: Relation between luminescence of starting materials and luminescence of single crystals
Optical Materials, 2009
A relation between photoluminescence (PL) characteristics of different starting materials used for crystal growth and un-doped sapphire single crystals manufactured using various methods of crystal growth (Kyropolus, HEM, Czochralski, and EFG) was found. The crystals grown using the Verneuil starting material exhibited significant PL when any method of crystal growth was used. On the contrary, sapphire samples grown by the same technologies wherein the starting material was EMT HPDA R revealed very low PL.