Glow curves and the emission of BaFCl:Eu2+

Thermoluminescence and the emission of γ-irradiated BaFCl:Eu²⁺ has been studied. A well defined glow peak at 400 K and a shoulder at 480 K are obtained in addition to those obtained as in undoped BaFCl. Thermoluminescence emission has shown a band at about 390 ∼ 400 nm. Additional glow peaks have been attributed to the luminescence centers as caused by europium impurity.     

Glow curves of flux-grown NaMgF3 crystals

Glow curves and optical absorption spectra of X-irradiated flux grown crystals are studied. Two glow peaks at 370, 585 K and three shoulders at 420, 540 and 610 K are obtained. Optical absorption studies reveal two absorption bands at 405 and 475 nm and a well defined peak at 295 nm. Room temperature annealing and bleaching studies have suggested that the glow peaks at 370 and 585 K may correspond to impurities and F-centers of 295 nm band respectively. The other shoulders at 420, 540 and 610 K are attributed to other F-aggregate centers. The glow peaks are analysed using first order kinetics.     

Effect of lattice oxygen on optical absorption, radiation hardness and thermally stimulated luminescence of BaF2 crystal

The influence of the presence of BaO impurity on the optical absorption, radiation hardness and thermally stimulated luminescence of BaF₂ has been investigated. The presence of oxygen impurity gives rise to three absorption bands in the UV region, peaking around 220, 280 and 335 nm. Further, the impurity is found to be detrimental to crystal hardness against ionizing radiations. The thermally stimulated luminescence (TSL) has been studied from gamma-irradiated crystals containing different fractions of BaO impurity. Four prominent glow peaks around 100°C (peak I), 150°C (peak II), 220°C (peak III) and 290°C (peak IV) are observed for crystals containing BaO impurity concentrations lower than 0.5% (by wt). For crystals containing higher impurity concentrations, two additional peaks around 75°C and 260°C are also observed. The kinetics of TSL emission is observed to be of first order, implying that the absorption and the emission centers responsible for TSL are the same. The normalized TSL output for peak I is found to vary linearly with the concentration of oxide impurity. This fact can be utilized to detect the presence of minute amounts of oxygen in BaF₂ lattice, which is crucial to the growth of crystals exhibiting high radiation hardness.     

Thermoluminescence and Optical Absorption Studies of Z1 Centers in KCI Crystals Doped with Praseodymium

Thermoluminescence (TL) of Pr-doped KCI is studied. The influence of pre-heat treatment and optical bleaching of the glow curves and the production of Z₁ centers are discussed. The glow curves of KCI containing 1062 ppm of praseodymium (Pr) shows one shoulder at 365 K (T₁) and two peaks around 408 K (T₂) and 443 K (T₃), respectively. Bleaching of X-irradiated crystals shows that the peak T₂ is enhanced whereas other two (T₁, T₃) get suppressed. Optical absorption studies of the crystals before and after F-bleaching shows that the F-band decreases and shifts towards longer wavelengths. The decrease is accompanied by broadening towards the longer wavelength. The T₂ peak is attributed to Z₁ centres. It is shown that T₁ corresponds to shallow centers and T₃ peak is attributed to F-centers.     

Preparation and upconversion luminescence characterization of 12CaO·7Al2O3:Ho3+/Yb3+ polycrystals

The effect of Yb³⁺ concentration on the fluorescence of 12CaO·7 Al₂O₃:Ho³⁺/Yb³⁺ polycrystals is investigated. The Raman spectra of pure C12A7 under 633‐nm excitation show that the highest photon energy is 787.267 cm⁻¹, which is not much bigger than general fluorides, so it can realize high efficiency upconversion. The upconversion emission spectra suggest that the green upconversion emission centered at 548 nm and the red upconversion emission at 662 nm correspond to the ⁵F₄/⁵S₂→⁵I₈ and ⁵F₅→⁵I₈ transition of Ho³⁺ ions, respectively. The intensity of the upconversion luminescence and the ratio of red to green are changed with Yb³⁺ ion concentration. The pump dependence and luminescence decay dynamics spectra show the green and red upconversion emissions are populated by a two‐photon process, and the upconversion mechanisms are analyzed. The relative luminous efficiencies of green and red emissions are 2.035% and 0.7%, respectively. The normalized efficiency obtained for green emission of Ho³⁺ at RT when the sample is excited by 980‐nm light with an absorbed intensity of 7.5 W/cm² is 0.27 cm²/W. This result is comparable to the values obtained in YF₃ for the Yb³⁺, Er³⁺ green emission. The C12A7 with upconversion red and green light will be a promising luminous material.     

Novel Bi-doped glasses for broadband optical amplification

Broadband infrared luminescence is observed in various Bi-doped oxide glasses prepared by conventional melting-quenching technique. The absorption spectrum of the Bi-doped germanium oxide glass consists of five broad peaks at below 370, 500, 700, 800 and 1000 nm. The fluorescence spectrum exhibits a broad peak at about 1300 nm with full width at half maximum (FWHM) of more than 300 nm when excited by an 808 nm laser diode. The fluorescence lifetime at room temperature decreases with increasing Bi₂O₃ concentration. Influence of the glass composition and melting atmosphere on the fluorescence lifetime and luminescent intensity is investigated. The mechanism of the broadband infrared luminescence is suggested. The product of stimulated emission cross-section and lifetime of the Bi-doped aluminophosphate glass is about 5.0 × 10^?24 cm² s. The glasses might be promising for applications in broadband optical fiber amplifiers and tunable lasers.     

A thermoluminescence study of Z2-centres in terbium-doped NaCl crystals

Thermoluminescence (TL), optical absorption are used to correlate thermal annealing of Z₂-centres with TL peak occurring around 110 °C in Terbium doped NaCl crystals. The TL glow peak occurring around 190 °C it attributed to the thermal annealing of F-centres. The thermal activation parameters are calculated for both Z₂- and F-centre peaks.     

Growth of large-sized Ce:Y3Al5O12 (Ce:YAG) scintillation crystal by the temperature gradient technique (TGT)

In this work, Ce:YAG crystal with the size of ?4 in was successfully grown by the TGT method. The optical and scintillation properties of as-grown Ce:YAG crystals were investigated. Three obvious absorption bands at 223, 340 and 460 nm and two weak color-center absorption bands at 296 and 370 nm are observed in as-grown Ce:YAG crystal. Fluorescence with an emission peak at 398 nm is observed due to the color centers, and absorption bands of the color centers can be eliminated by annealing in O₂ or H₂ atmosphere at 1673 K for 24 h. Yellow-green fluorescence centered at 530 nm is found when the crystal was excited at 460 nm and the 530 nm excitation spectrum shows two peaks at 340 and 460 nm. X-ray fluorescence spectrum of as-grown crystal shows three emission peaks at 300, 360 and 530 nm. An average light output of 1360 phe/MeV and a single exponential decay with the decay time constant of 62.97 ns are found in as-grown Ce:YAG crystal.     

Electronic traps in mixed Si1−xGexO2 films

Thermally stimulated luminescence (TSL) and infrared (IR) spectroscopy were measured in plasma grown Si_1−xGe_xO₂ (x=0, 0.08, 0.15, 0.25, 0.5) with different thicknesses (12–40 nm). A comparison with the TSL properties of thermally grown SiO₂ and GeO₂ was also performed. A main IR absorption structure was detected, due to the superposition of the peaks related to the asymmetric O stretching modes of (i) Si–O–Si (at ≈1060 cm⁻¹) and (ii) Si–O–Ge (at 1001 cm⁻¹). Another peak at ≈860 cm⁻¹ was observed only for Ge concentrations, x>0.15, corresponding to the asymmetric O stretching mode in Ge–O–Ge bonds. A TSL peak was observed at 70°C, and a smaller structure at around 200°C. The 70°C peak was more intense in all Ge rich layers than in plasma grown SiO₂. Based on the thickness dependence of the signal intensity we propose that at Ge concentrations 0.25x0.5 TSL active defects are localised at interfacial regions (oxide/semiconductor, Ge poor/Ge rich internal interface, oxide external surface/atmosphere). Based on similarities between TSL glow curves in plasma grown Si_1−xGe_xO₂, thermally grown GeO₂ and SiO₂ we propose that oxygen vacancy related defects are trapping states in Si_1−xGe_xO₂ and GeO₂.     

Crystallization behaviour of an amorphous Ti50Be40Zr10 alloy

The crystallization behaviour of an amorphous Ti₅₀Be₄₀Zr₁₀ alloy during a continuous heating mode from room temperature to 973 K and isothermal annealing at temperatures above the glass transition temperature is examined by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS) measurement and large-angle X-ray diffractometry (LAXD). DSC indicated two well-defined exothermic peaks, a slight shoulder at the higher temperature side of the second peak and a small heat evolution at higher temperature. The Kissinger plot for the first and the second peak gives a straight line, from which the apparent activation energy is estimated to be 269 and 413 kJ/mol respectively; the enthalpies for the first and second crystallization process are 1.04 kJ/mol and 4.39 kJ/mol for a heating rate of 20 K/min. The SAXS intensities increase sharply after annealing at about 673 K (corresponding to the first peak in the DSC curves); the scattering is due to the formation of fine-scale crystalline Ti particles by the LAXD. The size of the particles does not change significantly while the number of scattering particles increases, indicating that the reaction is almost nucleation controlled and the growth is very limited. Another crystalline phase would appear in addition to the Ti particles on annealing at temperatures above about 753 K (corresponding to the second peak in the DSC curves), where the SAXS intensities decrease compared with those for only the first-stage of crystallization. The crystalline phase might be a metastable cubic phase with the lattice parameter a₀?0.2994 nm.The sequence in the crystallization of the initial non-crystalline material is amorphous → microcrystalline (MS I) → crystalline (MS II; S III), although the structure of crystalline phase in the final stage (S III) was not identified. It is also likely that cold-rolling does not have a perceptible effect on the crystallization behaviour of the present amorphous alloy.     

Fluorescence of copper, manganese and antimony ions in phosphate glass host

The paper presents a study based on luminescence characteristics of phosphate glasses containing Cu²⁺, Mn⁴⁺ and Sb³⁺. The glass samples obtained by a wet chemical route belong to Li₂O–BaO–Al₂O₃–La₂O₃–P₂O₅ oxide system. The oxide composition of the glass samples is calculated to obtain a vitreous network composed of metaphosphate chains bonded by modifier ions (Li⁺, Ba²⁺ and La³⁺) and fluorescent ions. The absorption spectra of the samples were acquired in the UV domain in order to establish the excitation wavelength for each fluorescent ion. The absorption peaks of Sb³⁺ ion are ranged at 285 nm and 250 nm, Mn²⁺ ion at 280 nm and 365 nm, Cu²⁺ ion at 295 nm and 313 nm. The luminescence peaks of Cu²⁺, Mn⁴⁺ and Sb³⁺ ions are found in the visible domain at different wavelengths, depending on the oxidation state and coordination symmetry of each fluorescent ion. The fluorescence of Sb³⁺ ion has a strong signal at 450 nm and a weak one at 465 nm, Mn²⁺ ion shows a fluorescence peak at 600 nm and the pair Cu²⁺/Cu⁺ ions reveals a fluorescence emission at 460 nm.     

Cathodoluminescence of Ge, Si, and O implanted SiO2 layers and the role of mobile oxygen in defect transformations

Thermally grown SiO₂ layers of thickness d=500 nm have been implanted by Ge⁺, Si⁺, and O⁺ ions of energy 350, 150, and 100 keV, respectively, and a uniform implantation dose of D_i=5×10¹⁶ ions/cm². Thus the implantation profiles are expected with a concentration maximum of nearly 4 at.% at the half-depth d_m≅250 nm of the SiO₂ layers. After thermal annealing to 900 °C for 1 h in dry nitrogen or vacuum the typical violet luminescence band (λ=400 nm) of the Ge⁺ implanted centers is increased more than 200-fold and the Ge luminescent center depth profile is shifted from about 250 to 170 nm towards the surface as determined by cathodoluminescence (CL) depth profiling. Implanting oxygen increases the red band (λ=650 nm) but does not affect the blue band (λ=460 nm). Silicon surplus increases the amplitude of the blue (B) luminescence, but reduces the amplitude of the red (R) one. Studying the irradiation dose dependence of these blue and red bands we have established defect kinetics in SiO₂ including six main defects and precursors, including the non-bridging oxygen hole center for the red luminescence, the twofold-coordinated silicon as the oxygen deficient center ODC(2) for the blue luminescence and the mobile oxygen as the main transmitter between precursors and the radiation induced defects. The kinetics are described by a set of eight differential equations which predict the dose dependence of the CL.     

Effect of Flux on thermoluminescence in Flux-grown BaFCl crystals

BaFCl crystals have been grown using BaF₂ and BaCl₂ by flux technique. Glow curves, optical absorption, and TL emission spectra of x/r — irradiated crystals are studied. The results have been compared with those BaFCl crystals grown from NaF flux so as to study the effects of flux on these properties. It is found that crystals grown from BaF₂ flux are relatively purer. An additional TL glow peak at 460 K, an optical absorption band at 775 nm and TL emission band at 485 nm have been obtained in the presently grown crystals. The additional glow peak, optical absorption band have been attributed to F(¯F) aggregate centers, whereas the 485 nm TL emission band to impurity centers.     

Drawing induced absorption loss in multicomponent glass fibres

A drawing induced loss has been found to exist in multicomponent glass optical fibres, and has been shown to be due to absorption. Two loss peaks were identified at 580 and 360 nm with peak heights of 340 and 490 dBkm^?1, respectively. The 580 nm peak was believed to be due to silicon oxygen hole centres formed during fibre drawing. The induced loss could be partially removed by annealing, and the behaviour of the induced loss under various heat treatments was investigated. It was also found that the loss could be completely eliminated by the addition of 0.1 wt% As₂O₃ to the glass melt.     

Up-conversion enhancement in Er3 +-Ag co-doped zinc tellurite glass: Effect of heat treatment

The melt quenching method was used to synthesize the Ag⁰ nanoparticles and Er^3 + ions co-doped zinc tellurite glass. The glasses were characterized by differential thermal analyzer, UV–VIS-IR absorption, photoluminescence spectroscopy and TEM imaging. Heat treatment at different annealing time intervals above the glass transition temperature was applied to reduce the Ag⁺ ions to Ag⁰ NPs. The influence of heat treatment on structural and optical properties is examined. Intense and broad up-conversion emissions of silver are recorded in the visible region. Up-conversion luminescence spectra revealed three major emission peaks at 520, 550 and 650 nm originating from ²H_11/2, ⁴S_3/2 and ⁴F_9/2 levels, respectively. An efficient enhancement in visible region is observed for samples containing silver NPs. The absorption plasmon peaks are evidenced around 560 and 594 nm. The effect of localized surface plasmon resonance and the energy transfer from the surface of silver NP to trivalent erbium ions are described as the sources of enhancement.     

Thermoluminescence of Sr1–xEuxF2 + x Solid Electrolytes

Thermoluminescence (TL) studies have been carried out in different compositions of Sr_1–xEuxF_{2 + x} mixed crystals as a function of X-irradiation time. Three groups of TL glow peaks in the temperature ranges (340, 360 ∼ 370 K), (460 ∼ 475, 540 ∼ 575 K) and (615 ∼ 635, 680 ∼ 720 K) are identified. The growth rates of different glow peaks have been compared with each other to estimate the growth kinetics. The three groups of TL glow peaks are attributed to thermal ionization of radiative impurity centers, different stages of F-centers and other kinds of defect centers such as F-interstitials. The shift in the glow peak maxima is perhaps due to unassociated impurities surrounding F-centers causing a change in configuration. The concentration quenching of TL output due to increased europium is pertinent in Sr_1–xEuxF_{2 + x} mixed system.     

Low temperature TL glow curves in KBrxI1-x mixed crystals

Thermoluminescence (TL) glow curves were recorded in KBr, KI and in different compositions of KBr_xI_1-x mixed crystals at LNT. For this a cryostat has been designed and fabricated. The glow peaks observed in these crystals have been attributed to differnent colour centers.     

Studies on the growth and optical characterization of Tm3+‐doped BaY2F8 single crystals

The BaY₂F₈ crystals doped with different concentrations of Tm³⁺ ions were prepared by the temperature gradient technique (TGT). X‐ray powder diffraction was applied to analyze the phase. The cracking phenomenon along (010) and (100) planes of the crystals grown by temperature gradient technique was studied on the basis of the structure of BaY₂F₈ crystals. The absorption spectra were measured and investigated in the ultraviolet‐visible and near‐infrared ranges at room temperature. Several characteristic absorption bands of Tm³⁺‐doped BaY₂F₈ crystal were observed. The emission and excitation spectra were obtained and investigated at room temperature and 12 K, showing the characteristic emission peaks of Tm³⁺ ions. The temperature dependence of Photoluminescence curve was also investigated in the range of 12–296 K. The luminescence intensity of emission bands decreased with increasing temperature, while the effective bandwidth increased. The up‐conversion spectrum excited at 650 nm was recorded and up‐conversion mechanism was analyzed in detail. The result showed the purple, green and yellow emissions corresponding to ³P₁→³F₃, ¹D₂→³H₅ and ³P₀→¹G₄ transitions, respectively.     

Energy transfer up-conversion in Tm-doped silica fiber

A study of the mechanisms responsible for the infra-red to near infra-red up-conversion in Tm³⁺-doped silica fibers is presented. Up-conversion luminescence was observed from the ³H₄ level of Tm³⁺ under 1586 nm pumping into the ³F₄ level. The quadratic dependence of the up-conversion luminescence at 800 nm on the 1800 nm luminescence from the ³F₄ level confirms that the ³H₄ level is populated by a two photon process. Two possible processes are proposed as mechanisms responsible for the up-conversion: excited state absorption and energy transfer up-conversion. The decay characteristics of the luminescence from the ³H₄ level were studied under direct and indirect pumping at 786 and 1586 nm, respectively. By comparing the decay waveforms to the solution of a simple set of rate equations, the energy transfer up-conversion process (³F₄, ³F₄ → ³H₄, ³H₆) was established at Tm₂O₃ concentrations greater than 200 ppm.     

Thermally stimulated luminescence of Ce and Tb doped SiO2 sol–gel glasses

Thermally stimulated luminescence (TSL) properties of cerium and terbium doped SiO₂ sol–gel glasses were studied after X-ray irradiation in the temperature range 10–700 K. The role of Ce³⁺ and Tb³⁺ as recombination centers was shown. The existence of a distribution of trap levels was observed; the activation energies of such a distribution were calculated to extend from about 8 × 10⁻³ eV up to 1.8 eV for both cerium and terbium doped sol–gel glasses. The effect of a post-densification thermal treatment on TSL properties was also analyzed.