Optical studies in gamma irradiated Mg doped CaF2 single crystals

Pure and Mg doped CaF₂ single crystals grown by the Bridgman method were irradiated with gamma rays (γ-rays) for doses ranging from 97 Gy to 9.72 KGy. The pristine samples showed minimal absorption indicating the purity of the samples. The γ-irradiated pure CaF₂ crystals showed prominent and strong absorption with a peak at ~ 374 nm besides three weak ones at ~ 456, 523 and 623 nm. However γ-rayed Mg doped crystals showed a prominent absorption with a strong peak at ~ 370 nm and a broad one at ~ 530 nm. The absorption indicated the generation of F and F-aggregate centers in the irradiated crystals. The photoluminescence (PL) emission spectrum of both pure and Mg doped crystals showed prominent emission at ~ 390 nm when they were excited at ~ 250 nm. Also, when the samples were excited at 323 and 363 nm strong emissions were observed at ~ 430 and 422 nm respectively. The optical absorption and PL intensities were found to increase with increase in dose.     

Optical studies of samarium-doped fluoride nanoparticles

Samarium-doped calcium fluoride (CaF₂) nanoparticles were synthesized by the co-precipitation method and characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), optical absorption and photoluminescence (PL) techniques. The PXRD patterns confirmed the cubic crystallinity of the synthesized nanoparticles. The average particle size estimated using Scherer's formula was ～20?nm. The purity of the synthesized nanoparticles was confirmed by the FTIR spectrum. The morphological features studied using SEM revealed that the nanoparticles were agglomerated and porous. The optical absorption spectrum showed a strong and prominent absorption peak at ～264?nm and a weak one at ～212?nm. The PL spectrum showed broad and prominent emissions with peaks at ～387 and 532?nm along with weak emissions at 573 and 605?nm.     

100 MeV Si8+ ion induced luminescence and thermoluminescence of nanocrystalline Mg2SiO4:Eu3+

Nanoparticles of Mg₂SiO₄:Eu³⁺ have been prepared by the solution combustion technique and the grain size estimated by PXRD is found to be in the range 40–50 nm. Ionoluminescence (IL) studies of Mg₂SiO₄:Eu³⁺ pellets bombarded with 100 MeV Si⁸⁺ ions with fluences in the range 1.124–22.48×10¹² ions cm^?2 are carried out at IUAC, New Delhi, India. Five prominent IL bands with peaks at 580 nm, 590 nm, 612 nm, 655 nm and 705 nm are recorded. These characteristic emissions are attributed to the luminescence centers activated by Eu³⁺ cations. It is found that IL intensity decreases rapidly in the beginning. Later on, the intensity decreases slowly with further increase of ion fluence. The reduction in the ionoluminescence intensity with increase of ion fluence might be attributed to degradation of Si–O (ν₃) and Si–O (2ν₃) bonds present on the surface of the sample. The red emission with peak at 612 nm is due to characteristic emission of ⁵D₀→⁷F₂ of the Eu³⁺ cations. Thermoluminescence (TL) studies of Mg₂SiO₄:Eu³⁺ pellets bombarded with 100 MeV Si⁸⁺ cations with fluences in the range 5×10¹¹ ions cm^?2 to 5×10¹³ ions cm^?2 are made at RT. Two prominent and well resolved TL glows with peaks at ～220 °C and ～370 °C are observed. It is observed that TL intensity increases with increase of ion fluence. This might be due to creation of new traps during swift heavy ion irradiation.     

Luminescence studies on swift heavy ion irradiated nanocrystalline aluminum oxide

Pellets of nanocrystalline aluminum oxide synthesized by a combustion technique are irradiated with 120 MeV Au⁹⁺ ions for fluence in the range 5×10¹¹-1×10¹³ ions cm⁻². Two photoluminescence (PL) emissions, a prominent one with peak at ∼525 nm and a shoulder at ∼465 nm are observed in heat treated and Au⁹⁺ ion irradiated aluminum oxide. The 525 nm emission is attributed to F₂²⁺-centers. The PL intensity at 525 nm is found to increase with increase in ion fluence up to 1×10¹² ions cm⁻² and decreases beyond this fluence. Thermoluminescence (TL) of heat-treated and swift heavy ion (SHI) irradiated aluminum oxide gives a strong and broad TL glow with peak at ∼610 K along with a weak shoulder at 500 K. The TL intensity is found to increase with Au⁹⁺ ion fluence up to 1×10¹³ ions cm⁻² and decreases beyond this fluence.     

Damage creation in swift heavy ion-irradiated calcite single crystals: Raman and infrared study

Raman and Infrared studies were carried out on pristine and 100 MeV Ag(8+) ion irradiated calcite single crystals in the fluence range 1 x 10(11) to 1 x 10(13)ions/cm(2). Raman and Infrared modes were assigned according to factor theory analysis. It is observed that the intensities of the Raman and infrared bands decrease with increase of ion fluence. The decrease of these bands is attributed to breakage of carbonate ions and other details are discussed.     

Morphology and optical properties of Mg and Sr doped CaF2 nanocrystals

Magnesium (Mg) and Strontium (Sr) doped Calcium fluoride nanocrystals were synthesized by co-precipitation method. The cubic structure of the samples was confirmed by Powder X-ray diffraction. The average crystallite size of Mg doped samples was found to be ~ 25 nm whereas in Sr doped one it was ~ 35 nm. The morphological features revealed that the nanocrystals were agglomerated, crispy and porous. The as-prepared samples showed the presence of hydroxyl groups. The optical absorption spectrum of as-prepared Mg doped samples showed a strong absorption band peaked at ~ 233 nm whereas the Sr doped one showed a prominent absorption peak at 248 nm. A strong PL emission was observed at ~ 300 nm in Mg doped samples. However, the Sr doped samples showed two prominent emissions at ~ 345 and 615 nm.     

Ionoluminescence studies of combustion synthesized Dy doped nano crystalline forsterite

Ionoluminescence (IL) of nano crystalline Mg₂SiO₄:Dy³⁺ pellet samples bombarded with 100 MeV Si⁺⁸ ions with fluences in the range (1.124–22.480) × 10¹² ions cm⁻² have been studied. Two prominent IL bands with peaks at ∼480 nm and ∼580 nm and a weak band with peak at ∼670 nm are recorded. The characteristic peaks are attributed to luminescence center activated by Dy³⁺ ions due to the transitions ⁴F_9/2→⁶H_15/2,⁶H_13/2 and ⁶H_11/2. It is found that IL intensity initially decreases rapidly and then continuous to decrease slowly with further increase in ion fluence. The reduction in the Ionoluminescence intensity with increase of ion fluence might be attributed to degradation of Si–O ( 2ν₃) bonds present on the surface of the sample and/or due to lattice disorder produced by dense electronic excitation under heavy ion irradiation.     

Effect of substitution of Ce on superconducting properties of Bi1.7Pb0.3Sr2Ca2−x Ce x Cu3O10+δ system

We have investigated the superconducting properties of the Bi_1.7 Pb_0.3Sr₂Ca_2−xCe _x Cu₃O_10+δ system with x=0.00, 0.02, 0.04, 0.08 and 0.1 by X-ray diffraction and magnetic susceptibility. The substitution of Ce for Ca has been found to drastically change the superconducting properties of the system. X-ray diffraction studies on these compounds indicate decrease in the c-parameter with increased substitution of Ce at Ca site and volume fraction of high T _c (2 : 2 : 2 : 3) phase decreases and low T _c phase increases. The magnetic susceptibility of this compound shows that the diamagnetic on set superconducting transition temperature (onset) varies from 109 K to 51 K for x=0.00, 0.02, 0.04, 0.08 and 0.1. These results suggest the possible existence of Ce in a tetravalent state rather than a trivalent state in this system; that is, Ca²⁺ → Ce⁴⁺ replacement changes the hole carrier concentration. Hole filling is the cause of lowering T _c of the system.     

Self-assembled growth of nanostructural Ge islands on bromine-passivated Si(111) surfaces at room temperature

We have deposited relatively thick (∼60 nm) Ge layers on Br-passivated Si(111) substrates by thermal evaporation under high vacuum conditions at room temperature. Ge has grown in a layer-plus-island mode although it is different from the Stranski-Krastanov growth mode observed in epitaxial growth. Both the islands and the layer are nanocrystalline. This appears to be a consequence of reduction of surface free energy of the Si(111) substrate by Br-passivation. The size distribution of the Ge nanoislands has been determined. The Br-Si(111) substrates were prepared by a liquid treatment, which may not produce exactly reproducible surfaces. Nevertheless, some basic features of the nanostructural island growth are reasonably reproducible, while there are variations in the details of the island size distribution.