Ray Excitation Research Articles

Tunable Luminescent Properties and Multifunctional Imaging Applications of (Gd1-xRx)2O2S:Tb3+ (R = Y, La) Phosphor and Screen.

Gd2O2S:Tb3+ phosphor screens are widely used in image intensifiers, computed tomography, and neutron imaging. To improve the luminescent properties and thermal stability, (Gd1-xRx)2O2S:yTb3+ (R = Y, La) (x = 0, 0.05, 0.15, 0.25, and 0.35; y = 0.02, 0.04, 0.06, 0.08, and 0.10) phosphors were successfully prepared by the carbothermal reduction method. The luminescent spectra showed that the optimum concentrations of Tb3+ ions were 6 and 4 mol % when excited by 292 nm UV light and cathode ray, respectively. The emission wavelengths mainly peaked at 489 and 544 nm. It was found that the introduction of Y3+ ions could improve the luminescent intensity, and the luminescent intensity of (Gd1-xYx)2O2S:0.06Tb3+ was the highest at x = 0.25, while La3+ ions played the opposite role. Then, the thermal stability also improved, and the emission intensities of Gd2O2S:0.06Tb3+, (Gd0.75Y0.25)2O2S:0.06Tb3+, and (Gd0.75La0.25)2O2S:0.06Tb3+ phosphors at 423 K decreased to 66.22%, 68.23%, and 76.10% of the emission intensities at 303 K, respectively. Finally, the (Gd0.75Y0.25)2O2S:0.06Tb3+ phosphor screen was successfully prepared by the gravity deposition method and could be well imaged under UV light and cathode ray excitation with a CMOS camera. In summary, this study demonstrates that (Gd1-xRx)2O2S:Tb3+ (R = Y, La) is a phosphor with excellent luminescent and thermal stability properties and has great potential for application in the field of low-level-light night vision, nondestructive testing, and medical imaging.

Response of Lead Fluoride (PbF2) Crystal under X-ray and Gamma Ray Radiation

Background: In this research, the response of a 10 × 10 × 10 mm3 commercially available PbF2 crystal was experimentally assessed under X-ray and gamma ray radiation to verify the possible application of this material in X-ray medical imaging. Methods: The measurements were performed under X-ray from 50 to 130 kVp and gamma ray excitation (Tc-99m 140 keV and I-131 365 keV). The PbF2 response was experimentally assessed by the determination of the absolute luminescence efficiency (AE), X-ray luminescence efficiency (XLE), and the stopping power of this scintillating crystal in terms of the energy absorption efficiency (EAE). The results were compared with bismuth germanate (BGO) crystal, which is commonly used in medical imaging modalities. Results: The AE of PbF2 gradually decreased from 50 kVp up to 130 kVp. The maximum value was 0.61 efficiency units (EU) at 140 keV, and the minimum value was 0.03 EU at 71 keV (130 kVp). Similarly, low values appeared for the XLE, where the maximum value was 16.9 × 10−5 at 140 keV. Conclusions: These findings show that the PbF2 scintillator has unacceptably low luminescence efficiency. Although PbF2 can effectively absorb radiation, the scintillation light, at room temperatures, is negligible, and, thus, it could not be used in medical imaging applications in the examined energy range.

Label-free multiphoton excitation imaging as a promising diagnostic tool for breast cancer.

Histopathological diagnosis is the ultimate method of attaining the final diagnosis; however, the observation range is limited to the two‐dimensional plane, and it requires thin slicing of the tissue, which limits diagnostic information. To seek solutions for these problems, we proposed a novel imaging‐based histopathological examination. We used the multiphoton excitation microscopy (MPM) technique to establish a method for visualizing unfixed/unstained human breast tissues. Under near‐infrared ray excitation, fresh human breast tissues emitted fluorescent signals with three major peaks, which enabled visualizing the breast tissue morphology without any fixation or dye staining. Our study using human breast tissue samples from 32 patients indicated that experienced pathologists can estimate normal or cancerous lesions using only these MPM images with a kappa coefficient of 1.0. Moreover, we developed an image classification algorithm with artificial intelligence that enabled us to automatically define cancer cells in small areas with a high sensitivity of ≥0.942. Taken together, label‐free MPM imaging is a promising method for the real‐time automatic diagnosis of breast cancer.

A high-speed radiation imaging system based on liquid scintillator filled capillary arrays.

A high-speed radiation imaging system based on an image converter of liquid scintillator filled capillary arrays has been developed, which is sensitive to x rays, gamma rays, and neutrons. This imaging system has advantages of both high spatial resolution and high sensitivity because increasing the thickness of the image converter only leads to little deterioration on imaging resolution. The capillary arrays have dimensions of 150mm diameter and 50mm thickness, with 100 µm diameter of each capillary. The fluorescence decay time of the filled liquid scintillator based on the mixture of p-xylene and 2,5-diphenyloxazole has been evaluated to be ∼3ns with the single photon method under the gamma ray excitation. The spatial resolution has been experimentally evaluated to be about 1.15 and 0.6mm, under excitation of x rays and neutrons, respectively. The imaging system has been applied for diagnosing the dynamic x-ray spot generated by the rod pinch. Two frames in single shot with 15ns temporal resolution and 20ns inter-frame separation time have been obtained, which show the spatiotemporal distribution of the electrons bombarding the tungsten rod, indicating the ability of this imaging system in diagnosing dynamic radiation objects. In addition, the technique of capillary arrays provides a promising path for applications of advanced liquid scintillators in the field of radiation imaging.

Effect of H2O Molecule Adsorption on the Electronic Structure and Optical Properties of the CsI(Na) Crystal.

We investigated H2O molecule adsorption that had an effect on the luminescence properties of the CsI(Na) crystal using experiments and first-principle calculations. We measured the emission spectra of the CsI(Na) crystal at different exposure times under gamma ray excitation. The experimental results showed that the energy resolution of the CsI(Na) crystal was worse when the crystal surface adsorbed more H2O molecules, and the crystal surface deliquescence decreased the luminescence efficiency of the CsI(Na) crystal. We studied the band structure, density of states, and optical properties changes caused by H2O molecule adsorption on the CsI(Na) (010) surface. The generalized gradient approximation (GGA) was used to describe the exchange and correlation potential between the electrons. Our calculation results showed that the band gap width of the CsI(Na) (010) surface decreased after adsorbing H2O molecules, while three new peaks appeared in the valence band, and the absorption coefficient decreased from 90,000 cm−1 to 65,000 cm−1, and the reflection coefficient decreased from 0.195 to 0.105. Further, the absorption coefficient was reduced by at least 25% because of H2O molecule adsorption, which led to the luminescence degradation of the CsI(Na) crystal.

Novel reddish-orange emitting ultraphosphate CaP4O11:Eu3+ phosphor: Synthesis and photoluminescence properties

In the present work, CaP4O11 was explored as a host material of phosphors for solid-state lighting applications for the first time. This ultraphosphate compound doped with Eu3+ ions was prepared via the solid-state reaction in air atmosphere. The photoluminescence properties were investigated under (UV) ray excitation. From a powder X-ray diffraction analysis, structural Rietveld refinement and IR/Raman spectroscopy, the formation of single phase CaP4O11 with a monoclinic structure was confirmed. The spectral distribution of the Eu3+ -doped CaP4O11 ultraphosphate results in an overall orange-red emission due to the non-negligible intensity of the 5D0→7F1 transition. One Eu3+ center was attributed according to the crystal structure and the luminescence characteristics. The luminescence decay curve of CaP4O11:Eu3+ was fitted into a single exponential function and the lifetime was about 3.8 ms. The obtained CaP4O11:Eu3+ phosphors may have a potential application for solid state lighting based on light emitting diodes technology.

Tapered fiber radiation sensor based on Ce/Tb:YAG crystals for remote γ-ray dosimetry.

A novel tapered fiber-optic radiation sensor (TFRS) based on cerium (Ce) and terbium (Tb) co-doped YAG scintillation crystals is demonstrated for the first time. Using the CO2 laser-heated method, a Ce/Tb:YAG crystal is well embedded into silica glass cladding without any cracks. The scintillation light emitted from the YAG scintillation crystal can be directly coupled into the derived silica optical fiber by the tapered region. The loss of the derived optical fiber is 0.14 dB/cm, which is one order of magnitude lower than the 1.59 dB/cm of the YAG crystal in the TFRS. Subsequently, strong photo- and radio-luminescence of Tb3+ (5D4→7F5) ions in TFRS are achieved under ultraviolet light and high-energy ray excitation, respectively. In particular, a prominent remote radiation response of the TFRS is presented under excitation by γ-rays through fusion splicing with multimode optical fibers. The response is approximately four times larger than that of a plastic scintillation fiber (BCF-12) sensor. Furthermore, the results possess high stability as well as a good linearity between the radiation dose rate and the response intensity. The TFRS in combination with an all-silica fiber system is a promising candidate for remote radiation detection.

Phase transition, radio- and photoluminescence of K3Lu(PO4)2 doped with Pr3+ ions

Luminescent characteristics of K3Lu(PO4)2:Pr3+ (1 and 5 mol.%) microcrystalline powders, a promising optical material for scintillation applications, were investigated using various experimental techniques. The material shows emission features connected with both high intensity interconfigurational 4f15d→4f2 transitions (broad UV emission bands) and intraconfigurational 4f2→4f2 transitions (weak emission lines in the visible range). The output of X-ray excited 4f15d→4f2 emission of Pr3+ increases with a temperature rise from 90 K to room temperature and higher depending on the Pr3+ ions concentration. The high 5% concentration of Pr3+ ions is found to be favourable for the stabilization of a monoclinic phase (P21/m space group) over a trigonal one (P3‾ space group) while emission properties of the material reveal that a phase transition occurs at higher temperatures. Decay kinetics of Pr3+ 4f15d→4f2 emission are recorded upon excitation with high repetition rate X-ray synchrotron excitation and pulse cathode ray excitation. Issues related to a non-exponential decay of luminescence and presence of slow decay components are discussed in terms of energy transfer dynamics. The presence of defects was revealed with thermoluminescence measurements and these are suggested to be the mainly responsible for delayed recombination of charge carriers on the Pr3+ 4f15d states. Some peculiarities of host-to-impurity energy transfer are discussed.

Testing performance of Pr3+-doped KLuP2O7 upon UV-, synchrotron X-ray and cathode-ray excitation

Abstract The luminescent characteristics of the double phosphate KLuP2O7 doped with Pr3+ ions, a promising optical material for scintillator applications, were investigated using various experimental spectroscopic techniques. KLuP2O7:Pr3+ shows Pr3+ emission associated with interconfigurational 4f15d1→4f2 transitions located in the UV range (250–320 nm), intraconfigurational 4f2→4f2 transitions (weak lines in the visible spectral range) and defect-related luminescence. The light output of X-ray or cathode ray excited Pr3+ 4f15d1→4f2 luminescence is found to be nearly independent of temperature in the range of 90–400 K. The output of pulsed cathode luminescence shows thermal quenching above 450 K characterized by an activation energy of about 0.5 eV. Upon excitation with pulsed cathode rays or high-frequency (~8 MHz) X-ray synchrotron radiation, the luminescence decay kinetics of Pr3+ 4f15d1→4f2 transitions are dominated by a decay component with lifetime of about 20 ns. An additional slower decay component with lifetime of 75 ns was observed upon cathode ray excitation and was shown to result from delayed host-to-impurity energy transfer. The latter, in turn, originates from re-trapping of charge carriers at defect-related traps whose presence was demonstrated by thermoluminescence measurements. Parameters of the trapping centers were estimated. Peculiarities of host-to-impurity energy transfer are analysed and discussed.

Tunable luminescence of Eu3+, Sm3+ and Dy3+ doped Na2CaMg(PO4)2 phosphor for optical applications

In this work Na2CaMg(PO4)2 and Na2CaMg(PO4)2-x(SO4)x doped with europium, samarium and dysprosium phosphors were synthesized by combustion method using urea as a fuel along with its optical, structural and morphological investigations which may be applicable for solid state lighting and near-UV excited LED. The phase homogeneity of the phosphor was established by X-ray powder diffraction (XRD) and characterized by scanning electron microscopy (SEM), photoluminescent (PL) spectroscopy and room temperature FTIR spectrum. The photoluminescence (PL) properties were investigated under ultraviolet (UV) ray excitation. Preliminary studies showed that the phosphor might be promising candidate as a light-conversion phosphor for the optical system. The luminescence intensity is enhanced considerably by tuning the host matrices after core–shell formation due to degree of decrease of non-radiative rates rising from surface sagging bonds and surpassing agent.

Nontoxic Carbon Quantum Dots/g‐C3N4 for Efficient Photocatalytic Inactivation of Staphylococcus aureus under Visible Light

The widespread use of antibiotics has caused the rapid emergence of antibiotic-resistant bacterial strains and antibiotic resistance genes in the past few decades. Photocatalytic inactivation, a promising approach for the killing of pathogens, efficiently avoids the problems induced by antimicrobial drugs. However, traditional photocatalysts usually have some disadvantages, such as high costs of raw materials, ultraviolet ray excitation, and potential leaching of toxic metals. Here, a metal-free heterojunction photocatalyst, denoted as CQDs/g-C3 N4 , is synthesized through incorporating carbon quantum dots (CQDs) on graphitic carbon nitride (g-C3 N4 ), which significantly enhances photocatalytic inactivation of Staphylococcus aureus (S. aureus) compared with pure g-C3 N4 in vitro. CQDs/g-C3 N4 causes a rapid increase of intracellular reactive oxygen species levels and destruction of cell membranes under visible light, eventually leading to death of bacteria. The efficacy of CQDs/g-C3 N4 is further examined by a mouse cutaneous infection model of S. aureus. CQDs/g-C3 N4 markedly reduces the bacterial loads and prompts lesion recovery in mice, as compared with g-C3 N4 -treated group. In vivo and in vitro toxicity analyses show that the side effects of CQDs/g-C3 N4 are negligible. Considering the efficient photocatalytic inactivation and nontoxicity of CQDs/g-C3 N4 , this visible-light-driven photocatalyst paves a brand new avenue for the treatment of S. aureus infection.

Tl2GdCl5 (Ce3+): A New Efficient Scintillator for X-and $\gamma$ -Ray Detection

We are in the process of developing novel thallium-based inorganic halide compounds for X- and $\gamma $ -ray radiation detections. In this paper, novel cerium-activated single crystals of Tl2GdCl5 are reported along with a pure Tl2GdCl5. The two-zone vertical Bridgman method is used to grow this scintillator from its melt. Luminescence studies are performed under ultraviolet and X-ray excitations at room temperature. All of the Ce-activated samples exhibit similar emission bands in the range of 350–430 nm, with a peak around 388 nm, attributed to the $5d~\to ~4f$ radiative transition of the Ce3+ ion. In the pure sample, an intense luminescence band appeared owing to the presence of the Tl+ ion in the host lattice, along with the typical Gd3+ emission (~310 nm). Scintillation properties, such as energy resolution, light yield, and decay time, are evaluated under the $\gamma $ -ray excitation. The scintillation properties vary with the Ce3+-concentration. The best performances are obtained for the 5-mol% Ce-activated crystal, which, under a 662-keV $\gamma $ -ray excitation, exhibited an energy resolution of 5% (full-width at half-maximum) and light yield of 53 000 ± 5300 ph/MeV. Fast scintillation decay components followed by slow components are observed for all grown samples. The measured scintillation properties of Tl2GdCl5, which has high density and effective Z-number, reveal its large potentials as a radiation detector in medical imaging techniques.

Impurity and defect-related luminescence of Ce3+ doped LiLa9(SiO4)6O2 crystals upon UV-VUV, X-ray and cathode ray excitation

We report on the synthesis and comprehensive characterization of Ce3+ doped LiLa9(SiO4)6O2 (LLSO) crystals, grown using the slow cooling flux method. The luminescence and optical spectroscopic properties and luminescence decay kinetics were studied upon excitation with UV, VUV, X-ray photons and cathode rays. Two impurity Ce3+ centres substituting for La3+- ions in two nonequivalent crystal positions are observed in LLSO:Ce3+. They are well distinguished spectroscopically in the UV range both in emission and excitation spectra. Apart from emission associated with Ce3+ 5 d→4f interconfigurational transitions, a low-temperature defect-related emission has been observed upon UV-VUV and higher energy X-ray excitation. Processes lying behind the temperature quenching and host-to-impurity energy transfer are analyzed and discussed.

Optical performance of Ca2P2O7:Ce3+ pyrophosphate phosphor synthesized via modified solid state diffusion

In the present study Ca2P2O7:Ce3+ pyrophosphate phosphor was synthesized by modified solid state diffusion. Materialization of crystalline phases were recognized by X ray diffraction pattern and their photoluminescence properties were studied using excitation and emission spectra under ultraviolet ray excitation ranging from 250 to 400 nm. The Ca2P2O7:Ce3+ phosphor was excited at 298 nm, the emission spectrum exhibited two intense bands at 362 nm and 390 nm emission due to 5d → 4f transitions of Ce3+ ions. The morphological investigations of Ca2P2O7 pyrophosphate have been carried out by scanning electron microscopy and fourier transform infrared spectra at room temperature was also examined. Stoke's shift, type of interaction between activator and the influences of the doping concentration of Ce3+ on the luminescence characteristics are discussed from photoluminescence excitation and emission spectra.

Spectroscopic investigations of Dy3+ activated MCaP2O7 (M = Sr/Ba) pyrophosphate phosphors

The dysprosium activated SrCaP2O7 and BaCaP2O7 phosphors were synthesized by solid-state diffusion technique and studied for their phase uniformity by X-ray diffraction pattern (XRD). Besides, photoluminescence (PL) properties under ultraviolet (UV) ray excitation have been investigated. Photoluminescence (PL) excitation spectrum measurement shows these phosphors can be efficiently excited by near-ultraviolet (UV) light from 300 to 400 nm and presents dominant luminescence band centered at around 470–490 nm (blue) and 575 nm (yellow). A scanning electron microscope (SEM) shows an average crystallite size in sub-micrometer range. The room temperature FTIR spectrum was investigated to study the nature of the chemical bonds and their molecular environment. CIE chromaticity coordinates values are estimated from emission spectra of SrCaP2O7:Dy3+ and BaCaP207: Dy3+ for the prepared samples. The obtained results indicate that these phosphors have possible applications in the lamp industry especially for solid state lighting and n-UV LED. The investigations on quantum efficiency, quantum yield and the energy band gap will be carried out in near future for the present phosphors.

On the Photo- and Cathodoluminescence of LaB3O6:Gd,Bi, Y3Al5O12:Pr, Y3Al5O12:Gd, Lu3Al5O12:Pr, and Lu3Al5O12:Gd

Y3Al5O12 (YAG) and Lu3Al5O12 (LuAG) doped with rare earth elements are widely used as scintillators, solid state lasers, and phosphors in white light emitting diodes (LEDs). Additionally, (Gd,La)B3O6:Bi has found application as a UV-B emitting phosphor in fluorsecent lamps a long time ago. This paper reports both the photoluminescence (PL) and cathodoluminescence (CL) of Pr3+ or Gd3+ substituted YAG and LuAG in comparison to the widely applied UV-B phosphor (Gd,La)B3O6:Bi under vacuum ultra violet (VUV) and cathode ray excitation, respectively. The powder diffraction pattern, emission, excitation, and reflection spectra and a comparison of the luminescence efficiency are shown and discussed. It turned out that all investigated phosphors show efficient luminescence in the UV-B spectral range. Moreover, it is found that LuAG:Gd has the highest efficiency upon VUV and upon CL excitation too.

Lifetimes in Te124 : Examining critical-point symmetry in the Te nuclei

The Doppler-shift attenuation method following inelastic neutron scattering was used to determine the lifetimes of nuclear levels to 3.3-MeV excitation in $\phantom{\rule{0.16em}{0ex}}^{124}\mathrm{Te}$. Level energies and spins, $\ensuremath{\gamma}$-ray energies and branching ratios, and multipole-mixing ratios were deduced from measured $\ensuremath{\gamma}$-ray angular distributions at incident neutron energies of 2.40 and 3.30 MeV, $\ensuremath{\gamma}$-ray excitation functions, and $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence measurements. The newly obtained reduced transition probabilities and level energies for $\phantom{\rule{0.16em}{0ex}}^{124}\mathrm{Te}$ were compared to critical-point symmetry model predictions. The $E(5)$ and ${\ensuremath{\beta}}^{4}$ potential critical-point symmetries were also investigated in $\phantom{\rule{0.16em}{0ex}}^{122}\mathrm{Te}$ and $\phantom{\rule{0.16em}{0ex}}^{126}\mathrm{Te}$.

Detection of microscopic defects in optical fiber coatings using angle-resolved skew rays.

Microscopic defects in optical fiber coatings can be an impending catastrophe for high-power fiber laser and telecommunications systems and are difficult to detect with conventional methods. We demonstrate a highly sensitive interrogation technique that can readily identify faults such as microscopic nicks, scrapes, low-quality recoatings, and internal defects in fibers and their coatings, based on skew ray excitation and angle-resolved analysis.

Synthesis and luminescence properties of Tb doped LaBGeO5 and GdBGeO5 glass scintillators

Borogermanate glasses show promise as scintillators due to their ability to incorporate high levels of heavy metal oxides without excessive loss of luminescent output intensity. Heavy metal oxide scintillating glasses of 50GeO2-25B2O3-(25-x)La2O3/Gd2O3-xTb2O3 (x = 1,2,3,4) with the same stoichiometric composition of crystalline Tb doped LaBGeO5/GdBGeO5 were synthesized via the melt-quench method. Three times of higher light output under gamma ray excitation was observed from Tb doped GdBGeO5 based glass compared to LaBGeO5 glass due to efficient energy transfer between Gd-Tb pairs and higher luminescence efficiency in the GdBGeO5 glasses. The potential to form LaBGeO5/GdBGeO5 glass ceramic scintillators was also discussed and preliminarily investigated.

Scintillation Characterizations of Tin Doped Lithium Iodide Crystals at Room and Low Temperature

The crystals of 0.02%, 0.05%, 0.1%, and 0.5% Sn doped LiI are grown by the vertical Bridgman technique. The luminescence and scintillation properties of the grown crystals are investigated. X-ray excited emission spectrum of LiI (Sn) showed a broad emission band between 400–650 nm wavelength range at room temperature. Such emission is attributed to $\hbox {Sn}^{2 +}$ ion. Scintillation properties such as energy resolution, decay time profiles, and light yield are measured under 662 keV ( $^{137}\hbox {Cs}$ ) $\gamma $ -ray excitation at room temperature. A maximum light yield of $6000 \pm 600 \hbox{ph/MeV}$ is measured at room temperature. LiI (Sn) single crystals showed two exponential decay components under $\gamma $ -ray excitation. The dependence of scintillation properties on the temperature is also presented. Changes in the decay time and light yield are measured from 295 K down to 10 K. The light yield of LiI (Sn) at 50 K is found to be nine times higher than that at room temperature.