Photoluminescence, thermally stimulated luminescence and electron paramagnetic resonance investigations of Tb doped SrBPO5

Trap level spectroscopic studies were carried out on γ-irradiated Tb (1 mole%) doped SrBPO₅ were carried out using photoluminescence (PL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) techniques. The incorporation of Tb in the 3+ oxidation state was ascertained from PL studies. Life time for Tb³⁺ emission corresponding to the intense transition ⁵D₄ → ⁷F₅ at 543 nm was determined. The spectral characteristics of the TSL glows have shown that Tb³⁺ ions act as the emission center for the glow peak at 475 K. The trap parameters of the glow peak were determined. EPR investigations at room temperature/77 K revealed the stabilization of three boron oxygen hole trapped centers (BOHC's) and oxygen centered radicals such as O⁻ and O₂⁻ and trapped electrons in room temperature γ-irradiated samples. TSL glow peak at 475 K was found to be associated with recombination of electron released from trapped electron center and the BOHC₂ center.     

Thermally stimulated luminescence studies in combustion synthesized polycrystalline aluminum oxide

Synthesis of materials by combustion technique results in homogeneous and fine crystalline product. Further, the technique became more popular since it not only saved time and energy but also was easy to process. Aluminum oxide phosphor was synthesized by using urea as fuel in combustion reaction. Photoluminescence (PL) and thermally stimulated luminescence (TSL) characteristics of γ-irradiated aluminum oxide samples were studied. A broad PL emission with a peak at ∼ 465 nm and a pair of strong and sharp emissions with peaks at 679 and 695 nm were observed in γ-rayed samples. The PL intensity was observed to increase with increase in γ-ray dose. Two prominent and well resolved TSL glows with peaks at 210°C and 365°C were observed in all γ-irradiated Al₂O₃ samples. The TSL intensity was also found to increase with increase in γ-ray dose. The TSL glow curves indicated second order kinetics.     

Photoluminescence, thermally stimulated luminescence and electron paramagnetic resonance of europium-ion doped strontium pyrophosphate

Europium-ion doped strontium pyrophosphate was prepared via a chemical precipitation method to investigate the fluorescence of europium ions, the phosphate radical ions formed upon gamma-ray irradiation and their role in the thermally stimulated luminescence (TSL) of this compound. Fluorescence spectra revealed that europium ions were present in divalent as well as trivalent oxidation states. The measurements of fluorescence life time indicated that Eu³⁺ ions existed in two different types of environments in the lattice. Gamma irradiated europium-ion doped Sr₂P₂O₇ showed the presence of two thermo-luminescence glow peaks at 465 and 565 K; however, no glow was observed in the undoped sample. Electron paramagnetic resonance (EPR) studies of europium-ion doped samples showed signals from Mn²⁺ ions (present as impurity) prior to and after gamma irradiation. Upon gamma irradiation, signals originating from PO₂²⁻, PO₃²⁻ and O₂⁻ radical ions were observed in the undoped and doped samples. In the gamma irradiated europium-ion doped samples, additional low-field EPR signals, attributed to Eu²⁺ ions, were observed. By correlating the TSL and EPR results on europium-ion doped Sr₂P₂O₇, the mechanism for the glow peak at 565 K was identified.     

Erratum

Polycrystalline BaS phosphors have been prepared by reducing pure BaSO₄ with specpure carbon in argon atmosphere and doped with different quantities of Cu and Bi in the presence of NaCl flux. Thermally stimulated luminescence (TSL) and TSL spectra have been studied by exciting at 30°C (room temperature) with UV (200 nm), X-rays (30 kV,10 mA) and γ-rays (Co⁶⁰). While the traps produced by UV excitation give rise to prominent glow peaks only in the range 80–120°C, additional deeper and more stable traps (above 150°C) are produced by other exciting radiations. The relative intensity of the different glow peaks depends on the nature of the doped impurity and their associated complexes. The results are explained by considering the possible distribution of traps involving impurities and native defects.     

Band gap and trapping parameters of color tunable Yb3+/Er3+ codoped Y2O3 upconversion phosphor synthesized by combustion route

This paper reports the structural, optical and luminescence properties of Yb³⁺/Er³⁺ codoped Y₂O₃ phosphor synthesized by combustion method. The prepared phosphor was characterized by X-ray diffraction (XRD). XRD studies confirm the body-centered cubic structure of the phosphor. The optical properties such as diffuse reflectance (DR), photoluminescence and thermoluminescence were studied. DR spectra were used to determine the bandgap of the phosphor. Mechanism of upconversion by two-photon and energy transfer processes are interpreted and explained. The color coordinates were measured and the color tunability was analyzed as a function of the 980 nm excitation source power. Different trapping parameters associated with the glow peak were calculated by various glow curve methods.     

Long afterglow phosphorescent characteristics of BaAl2O4:Eu,Dy films

BaAl₂O₄:Eu,Dy (BAO) films have been fabricated on Si substrate by laser ablation, and their fundamental optical property and afterglow characteristics are discussed in comparison with the SrAl₂O₄:Eu,Dy (SAO) films. The intense green emission near 500 nm that originates from 5d to 4f transition in Eu²⁺ ions was clearly observed from the BAO films. This photoluminescence peak was at a shorter wavelength than that of the SAO films (λ = 520 nm). The afterglow intensity from the BAO films disappeared within a few minutes whereas that of the SAO films lasts over 20 min. The hole-trap depth (E_t) created by Dy as the auxiliary activators, which strongly affects the afterglow characteristics, was estimated on the basis of the thermally stimulated luminescence (TSL) result. The TSL glow curve for BAO films showed two broad peaks at 320 K and 450 K. The calculated E_t for each peak was 0.2 eV (for the 320 K peak) and 1.2 eV (for the 450 K peak). On the other hand, E_t = 0.5 eV was obtained from the SAO films. The hole-trap depths of the BAO film are either too shallow or too deep to affect the afterglow characteristics at room temperature.     

Optical properties of sol–gel derived Sr2SiO4:Dy3+ – Photo and thermally stimulated luminescence

Trivalent dysprosium-doped strontium silicate (Sr₂SiO₄) phosphors were prepared by sol–gel synthesis using tetra ethyl orthosilicate (TEOS) as precursor. The synthesis temperature could be brought down to 600 °C for formation of a single phase sample. The material was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), photoluminescence (PL), and thermally stimulated luminescence (TSL). The luminescence study revealed strong ⁴F_9/2 → ⁶H_13/2 transition at 577 nm (yellow), strong ⁴F_9/2 → ⁶H_15/2 transition at 482 nm (blue) and weak ⁴F_9/2 → ⁶H_11/2 transition at 677 nm (red), when excited by 250 nm (Charge transfer band, CTB) or 352 nm (f–f band). The concentration of the dopant ion and the temperature of annealing were optimized for maximum PL intensity. The critical energy-transfer distance for the Dy³⁺ ions was evaluated based on which, the quenching mechanism was verified to be a multipole–multipole interaction. The thermally stimulated luminescence studies of Sr₂SiO₄:Dy³⁺ sample showed main TSL glow peak at 413 K. The trap parameters namely activation energy (E), order of kinetics (b), and frequency factor (s) for this peak were determined using glow curve shape method.     

Correlation between thermoluminescence and mechanoluminescence of γ-ray-irradiated Dy-doped BaB<Subscript>4</Subscript>O<Subscript>7</Subscript> phosphors

Undoped and dysprosium (Dy)-doped BaB₄O₇ phosphors have been synthesised by solid-state diffusion technique and its thermoluminescence (TL) and mechanoluminescence (ML) has been studied. A single peak at 162 °C along with two shoulders around 242 and 294 °C was observed in TL glow curve of undoped BaB₄O₇ phosphors. TL intensity increased with increasing dopant concentration and broad band was observed for the sample having 0.5 mol% of dopant concentrations. For higher concentration of dopant, concentration quenching occurred. ML has been excited impulsively by dropping a piston of mass 0.6 kg on the phosphors with various impact velocities. As the piston was dropped on to the sample, ML intensity initially increased with time attained an optimum value for a particular time then decreased and finally disappeared. ML intensity varied with dopant concentration and it has been obtained optimum for the sample having 0.5 mol% of dopant. TL and ML intensity increased with gamma doses given to the sample. ML intensity increased almost linearly with the impact velocity of the piston dropped on to the sample, however, time corresponding to ML peak shifted towards shorter time value with increasing impact velocity of the piston dropped on to it. ML emission spectrum showed characteristic emission of Dy³⁺ ions. In order to study the influence of deformation on TL, TL was recorded after deforming the sample by dropping the load on to it. When the TL was recorded after deforming the sample, it is found that TL yield decreased markedly and it further decreased with increasing the height of the piston from which it was dropped. Results suggest that though the mode of excitation is different in these two phenomena but similar states are responsible for TL and ML.     

Thermally stimulated luminescence and photoluminescence investigations of Eu3+ and Eu2+ doped SrBPO5

Thermally stimulated luminescence (TSL) investigations of SrBPO₅:Eu^3?+ and SrBPO₅:Eu^2?+ phosphors were carried out in the temperature range of 300–650 K. In order to characterize the phosphors, X-ray diffraction and photoluminescence (PL) techniques were used. The emission spectrum of air heated SrBPO₅:Eu^3?+ phosphor exhibited emission bands at 590, 614, 651 and 702 nm under 248 nm excitation, assigned to transitions of Eu^3?+ ion. In phosphor prepared in reducing (Ar + 8% H₂) atmosphere, a broad emission band due to Eu^2?+ ranging from 350 to 400 nm was observed with 340 nm excitation. EPR studies have confirmed the presence of Eu^2?+ ions in the samples prepared in reducing atmosphere. TSL glow curve of SrBPO₅:Eu^3?+ had shown intense peaks around 397, 510, 547 K and a weak peak around 440 K whereas in case of SrBPO₅:Eu^2?+ system, glow peaks at 414, 478 and weak peak at 516 nm were observed. The shift in TSL glow pattern can be attributed to stabilization of different oxidation states of the dopant ion in the host lattice. Apart from this, TSL trap parameters such as trap depth and frequency factor were determined. Spectral characteristics of TSL emission have shown that Eu^3?+?/Eu^2?+ ion acts as the luminescent centre in the respective phosphors.     

Dosimeter properties of CaO transparent ceramic prepared by the SPS method

We have studied photoluminescence (PL), scintillation and thermally-stimulated luminescence (TSL) dosimeter properties of CaO transparent ceramic, in comparison with those of MgO transparent ceramic as a reference. Both samples were made by a Spark Plasma Sintering method. In the PL spectra, both samples showed emission peaks due to F and F⁺ centers. Moreover, in addition to these peaks, a scintillation emission peak was detected at 330 nm for both CaO and MgO, which was caused by surface defects. The TSL glow curves showed a main peak around 55 °C for CaO and 140 °C for MgO. The TSL response was confirmed to monotonically increase with irradiation dose over the dose range from 0.1 to 1000 mGy.     

Polymer-assisted synthesis and luminescence properties of MgAl2O4:Tb nanopowder

In the present work, terbium doped magnesium alluminate (MgAl₂O₄:Tb) nanopowder was synthesized by a polyacrylamide gel method. Structure, morphology and luminescence spectra were investigated by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL) measurements. The results showed that the single-phase MgAl₂O₄ could be formed at a relatively low temperature about 800 °C without unreacted Al₂O₃ and MgO phases. Powders with nanosized microstructures were formed. The polyacrylamide gel method resulted in a powder with smaller particle size and fewer agglomerates than the conventional sol-gel method. Luminescence analysis indicated that, the prepared MgAl₂O₄:Tb powders had strong green emission with ⁵D₄-⁷F₅ as the most prominent group. The emission intensity increased with increasing the calcination temperature.     

Spectral and trapping parameters of Eu3+ in Gd2O2S nanophosphor

This paper reports the structural, photometric, spectral and trapping parameters of Eu³⁺-doped gadolinium oxysulphide nanophosphor. The X-ray diffraction (XRD) data show the presence of the hexagonal phase of Gd₂O₂S and a crystallite size in nanometre range. Different structural parameters were calculated from XRD data. The Fourier transform infrared (FTIR) spectrum also confirms the formation of a compound. Scanning electron microscope studies reveal the morphology and crystallite size of the prepared phosphor. The band gap of the phosphor was calculated from diffuse reflectance spectra using the Kubelka–Munk function at 4.76 eV. The phosphor was illuminated with ultraviolet light and shows the characteristic red luminescence corresponding to ⁵D₀→⁷F_J transitions of Eu³⁺. The Judd–Ofelt intensity parameters and spectral parameters were estimated from the photoluminescence data. The nanophosphor was irradiated with γ-rays in the dose range 15–50 Gy for thermoluminescence (TL) studies and a shifting of the peak towards lower temperatures was observed with increasing γ-dose. Trapping parameters were calculated from TL data using various glow curve analysis methods.     

Investigation of thermoluminescence response and kinetic parameters of CaMgB2O5: Tb3+ phosphor against UV-C radiation for dosimetric application

The thermoluminescence (TL) response and kinetic parameters of CaMgB₂O₅:Tb³⁺ phosphor against UV-C radiations (λ?=?254 nm) had been investigated. The powder X-ray diffraction results confirm the formation of the monoclinic phase. TL results depict that the glow curve exhibited a broad peak centered at 430 K. The position and the shape of the curve were not influenced by the increase in dose, which is one of the requirements for dosimetric application. TL response curve was studied and showed a linear behavior against the studied dose (10–180 min). The effect of different heating rates on the TL intensity and the position of the glow peak were discussed in detail. In addition to this, the detailed examination of the glow peaks using variable heating rate and glow curve deconvolution methods was done to reveal the trapping parameters and to check the suitability of the present nanophosphor for UV-C dosimetry application.

     

Defect states in Pr doped lutetium pyrosilicate

We study defect states in Pr³⁺-doped Lu₂Si₂O₇ crystal by wavelength resolved thermally stimulated luminescence both below and above room temperature. We identify the TSL peaks, analyze them by the initial rise technique and calculate the characteristic parameters of the corresponding traps. The role of tunnelling of charge carriers between traps and recombination centers up to RT is observed and discussed. The TSL spectra show that the charge carrier recombination predominantly occurs at Pr³⁺ centers. We also provide some comparison with the LPS:Ce³⁺ crystal prepared by the same method.     

Synthesis and characterization of thorium phosphate phases by spray pyrolysis: chemistry of thorium phosphates

This paper describes the synthesis of some thorium phosphate compounds with different Th/P ratio (1/2, 2/3 and 3/4) by a spray pyrolysis technique. The so-prepared rough compounds were annealed at different temperatures for 2 h and then analyzed by mainly X-ray diffraction on powder and infrared spectroscopy. Every rough compound is composed by very badly crystallized ThO₂ phase polluted by carbon residue. An annealing treatment at 800 °C leads to the thorium diphosphate phase, α-ThP₂O₇ in every case. At 900 °C, such a phase is decomposed into a thorium phosphate diphosphate phase (Th₄(PO₄)₄P₂O₇, called TPD). However, a thorium excess in the initial mixture (Th/P = 3/4) leads also to observe the ThO₂ phase. The TPD phase is stable up to 1200 °C and does not react with the ThO₂ compound. Beyond 1200 °C, the TPD phase is slowly decomposed into a thorium phosphate compound which should be a thorium oxide phosphate; this compound does not contain any diphosphate species.     

The effect of Tb doping on the structure and spectroscopic properties of MgAl2O4 nanopowders

In this paper, a modified sol-gel method was employed to prepare nanostructured MgAl₂O₄ spinel powders doped with Tb³⁺ ions and thermally treated at 700 and 1000 °C for 3 h. The structural properties of the prepared at 700 and 1000 °C powders where characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). According to obtained XRD patterns the formation of single-phase spinels after calcination was confirmed. The XRD analyses demonstrated that the powders were single-phase spinel nanopowders with high crystallite dispersion. The Rietveld method was applied to calculate lattice parameters. The averaged spinel particle size was determined to be ∼10 nm for calcination at 700 °C and ∼20 nm at 1000 °C. The emission and excitation spectra measured at room and low temperature (77 K) for the samples calcined at 700 and 1000 °C demonstrated characteristic spectra of Tb³⁺ ions. The effect of MgAl₂O₄:Tb³⁺ grain sizes on luminescence properties was noticed.     

Scintillation and dosimeter properties of <Superscript>6</Superscript>LiF/CaF<Subscript>2</Subscript>:Eu eutectic composites

We investigated scintillation and dosimeter properties of ⁶LiF/CaF₂ eutectic composites doped with different concentrations of Eu (0.005, 0.02, 0.1, 0.3, and 1.0). In the photoluminescence (PL) and scintillation spectra, an emission peak at 430 nm due to the 5d–4f transitions of Eu²⁺ was observed. The intensity of PL and scintillation for ⁶LiF/CaF₂:0.005%Eu was the highest among the samples tested. In thermally stimulated luminescence (TSL), several glow peaks of ⁶LiF/CaF₂:0.005%Eu were observed after X-ray irradiation of 1000 mGy. The TSL response exhibited a linear response against X-ray dose over a dose range of 1–10,000 mGy. In optically stimulated luminescence (OSL), an emission peak was observed at 430 nm during a stimulation by 630 nm light after X-ray irradiation of 1000 mGy. The OSL intensity was the highest for ⁶LiF/CaF₂:0.005%Eu among all the samples investigated.     

ESR study for a TSEE peak in X-irradiated Li2B4O7:AgCl crystallized glass

Thermally stimulated exoelectron emission (TSEE) from X-irradiated crystallized glass of Li₂B₄O₇ doped with 0.03 mol% AgCl showed a conspicuous peak at 155° C, which is absent in an undoped sample. ESR analysis of the samples revealed that Ag⁰ atoms which had been formed by X-irradiation are responsible for the 155° C TSEE peak.     

Synthesis of CaAl2O4:Eu,Nd long persistent phosphor by combustion processes and its optical properties

Eu²⁺,Nd³⁺ co-doped calcium aluminate with high brightness and long persistent luminescence was prepared by the combustion method. The luminescent properties of CaAl₂O₄-based luminescent materials have been studied systematically. The phosphor powders were further investigated by X-ray diffractometer (XRD), photoluminescence excitation and emission spectra (PL) and brightness meter. The analytical results indicated that the phase of CaAl₂O₄ was formed when the initiating combustion temperature was 400 °C. The broad band UV excited luminescence of the CaAl₂O₄:Eu²⁺,Nd³⁺ was observed at the blue region (λ_max = 440 nm) due to transitions from the 4f⁶5d¹ to the 4f⁷ configuration of the Eu²⁺ ion. The decay time of the persistence indicated that the persistent luminescence phosphor has bright phosphorescence and maintains a long duration.     

A study of the phosphorescence mechanism of polycrystalline diamond films

A study of the phosphorescence mechanisms in polycrystalline diamond films was carried out through their thermoluminescent (TL) vanishing glow response. The polycrystalline diamond films phosphoresced when kept at room or higher temperatures after being excited with a UV light source. The observed behaviour of shallow and deep traps during the phosphorescence process can be explained with a simple time-dependent model. The diamond film phosphorescence was induced by exciting with a UV light source of 4 W and 254 nm wavelength. The TL vanishing glow curves were integrated from room temperature to 350°C at a linear heating rate of 10°C s^-1 in a N₂ atmosphere. The optical response of the diamond films was studied by means of its luminescence spectra, showing a broad emission band centered around 500 nm.