Enhancement of luminescence intensity and increase of emission lifetime in Eu-doped 3CdO-Al2O3-3SiO2 amorphous system

Intense photoluminescence at room temperature was observed in amorphous cadmium aluminum silicate doped with europium prepared by the sol-gel method. The structure of the 3CdO-Al₂O₃-3SiO₂:Eu³⁺ system (CAS:Eu³⁺) has been determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The excitation and the emission spectra indicated that the red characteristic emission (611 nm) of CAS:Eu³⁺ under UV excitation due to ⁵D₀→⁷F₂ electric dipole transition is the strongest. Both XRD data and the emission ratio of (⁵D₀→⁷F₂)/(⁵D₀→⁷F₁) reveal that the Eu³⁺ is in a site without inversion symmetry. The maximum photoluminescence intensity has been obtained for 25 mol% concentration of Eu³⁺ in CAS, and the intensity enhancement and lifetime increase of Eu³⁺ with increasing sintering temperature were observed due to the less OH-content in the samples.     

Effect of ZnO as modifier on up and downconversion properties of Ho/Yb doped tellurite glasses

Optical absorption and photoluminescent properties of Ho³⁺/Yb³⁺ co-doped tellurite and zinc tellurite glasses are investigated. The effect of zinc oxide as a modifier on the luminescence properties of above mentioned samples has been explored. Two intense upconversion emission bands centered at 546 (⁵F₄ + ⁵S₂ → ⁵I₈) and 660 nm (⁵F₅ → ⁵I₈) are observed on excitation with 976 nm diode laser. Zinc oxide acts as a quencher for 976 nm excited upconversion emission. The up and downconversion emission spectra are recorded with 532 nm excitation source also. In this case zinc oxide improves the up and downconversion emissions. A large enhancement in upconversion intensity has been observed when Ho³⁺ ion is co-doped with Yb³⁺ ion. The dependence of upconversion intensities on excitation power and on temperature has also been studied. The power dependence study shows a quadratic dependence of the fluorescence intensity on the excitation power while a decrement in emission intensity of all the transitions at different rates with increase in temperature is observed in temperature dependence study. The possible mechanisms are also discussed in order to understand the upconversion and energy transfer processes.     

Optimization of soft x-ray line emission from laser-produced carbon plasma with laser intensity

Absolute measurement for He-α resonance (1s^{2 1}S₀?1s2p¹ P ₁, at 40.2 Å) line emission from a laser-produced carbon plasma has been studied as a function of laser intensity. The optimum laser intensity is found to be ≈1.3×10¹² W/cm² for the maximum emission of 3.2 × 10¹³ photons sr^?1 pulse^?1. Since this line lies in the water window spectral region, it has potential application in x-ray microscopic imaging of biological sample in wet condition. Theoretical calculation using corona model for the emission of this line is also carried out with appropriate ionization and radiative recombination rate coefficients     

Luminescence optimization of Eu-doped LnAl3(BO3)4 (Ln=Y, Gd) red phosphor using spray pyrolysis

LnAl₃(BO₃)₄:Eu³⁺ (Ln=Y, Gd) red phosphor particles were prepared by spray pyrolysis and the luminescent intensity under vacuum ultraviolet (VUV) excitation was investigated by changing Eu³⁺ content, Y/Gd molar ratio, and boron content. The concentration quenching for Eu³⁺ activator was observed at 5 at%. The highest luminescent intensity at 615 nm due to the ⁵D₀→⁷F₂ transitions of Eu³⁺ was achieved when the ratio of Gd to Y was 0.55. The R/O ratio (obtained by dividing the red emission intensity at 615 nm with the orange one at 592 nm), however, was not influenced by the G/Y ratio. Using excess boron, up to 135% of the stoichiometric quantity, improved the emission intensity of LnAl₃(BO₃)₄:Eu³⁺ red phosphor. According to XRD analysis, the sample prepared using boron of a stoichiometric quantity had YBO₃ phase as a minor phase. Such YBO₃ phase progressively disappeared with an increase in the excess quantity of boron, which was responsible for the enhancement of emission intensity. In addition, the R/O ratio became larger and larger by increasing the excess content of boron due to a reduction in the symmetry of Y site. Consequently, both the emission intensity and the color coordinate of LnAl₃(BO₃)₄:Eu³⁺ red phosphors were successfully optimized in terms of the Y/Gd ratio and the excess quantity of boron in spray pyrolysis.     

Optical emission spectroscopy investigation of sputtering discharge used for SiOxNy thin films deposition and correlation with the film composition

The r.f. discharge of sputtering silicon target using argon-oxygen-nitrogen plasma was investigated by optical emission spectroscopy. Electronic temperature (T_e) and emission line intensity were measured for different plasma parameters: pressure (from 0.3 to 0.7 Pa), power density (0.6-5.7 W cm⁻²) and gas composition. At high oxygen concentration in the plasma, both T_e and the target self-bias voltage (V_b) steeply decrease. Such behaviour traduces the target poisoning phenomenon. In order to control the deposition process, emission line intensity of different species present in the plasma were compared to the ArI (λ = 696.54 nm) line intensity and then correlated to the film composition analysed by Rutherford Backscattering Spectroscopy.     

Luminescence from the Pr 4f5d and S0 states in LiLaP4O12

The photoluminescence and excitation spectra of Pr³⁺ activated LiLaP₄O₁₂ has been investigated in the 10-300 K temperature region. At all temperatures, the luminescence consists of optical transitions emanating from both the Pr³⁺ 4f¹5d¹ and the ¹S₀ states. However, at low temperatures the emission spectrum is dominated by the intraconfiguration emission transitions emanating from the Pr³⁺¹S₀ state. With increasing temperature, there is an exchange of intensity between the two emitting states; emission transitions from the ¹S₀ state exhibit strong intensity quenching while the 4f¹5d¹→4f² emission transitions reveal intensity gain. These results are explained on the basis of thermal population of the 4f¹5d¹ state by the ¹S₀ state. The energy barrier of 0.05 eV (403 cm⁻¹) for the nonradiative process is determined from the temperature dependence of the ¹S₀ lifetime.     

Conversion of infrared radiation into visible emission in NaY(WO4)2:Yb, Ho crystal

The spectroscopic characteristics and fluorescence dynamics for Yb³⁺/Ho³⁺:NaY(WO₄)₂ crystal were investigated. The parameters of oscillator strengths, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and the stimulated emission cross sections have been calculated based on Judd-Ofelt theory and Füchtbauer-Ladenburg method. The energy transfer efficiency from Yb³⁺ to Ho³⁺ was 65.85%. The green emission (530-570 nm) corresponding to (⁵F₄, ⁵S₂)→⁵I₈ transition, red emission (640-670 nm) due to ⁵F₅→⁵I₈ transition and NIR emission (740-770 nm) attributed to (⁵F₄, ⁵S₂)→⁵I₇ transition were observed on 974 nm excitation at room temperature. Under low pump power, the intensity of green light emission is weaker than that of the red light, while under high pump power, the case is on the contrary. The upconversion is based on the two-photon process either the energy transfer from Yb³⁺ ions or by the excited state absorption. The proposed mechanisms of upconversion emissions were provided.     

Preparation and photoluminescent properties of Ni-doped ZrO2 fibers

Ni²⁺-doped ZrO₂ precursor fibers were prepared via sol-gel technique by dry-spinning method and then heat-treated at different temperatures. The surface of the fibers is smooth with uniform diameter and no cracks have been observed by scanning electron microscopy (SEM). The emission intensity reaches a maximum value at 1 mol% Ni²⁺ because of the concentration quenching. The photoluminescence (PL) relative intensity is apparently intensifying with increasing temperature before 700 °C due to the crystallinity of the ZrO₂ lattice improvement. The PL results show that the typical emission center is at 510 nm excited at 315 nm.     

Enhanced photoluminescence of Ar implanted sapphire before and after annealing

In this paper, we studied the changes in the photoluminescence spectra of the Ar⁺ ion implanted mono-crystalline sapphire annealed at different atmospheres and different temperatures. Single crystals of sapphire (Al₂O₃) with the (1 0 1¯ 0) (m-samples) orientation were implanted at 623 K with 110 keV Ar⁺ ions to a fluence of 9.5×10¹⁶ ions/cm². Photoluminescence measurement of the as-implanted sample shows a new emission band at 506 nm, which is attributed to the production of interstitial Al atoms. The intensity of emission band at 506 nm first increased then decreased with increase in annealing temperature. For the same annealing temperature, the intensity of PL peak at 506 nm of the sample annealed in air was higher than the sample annealed in vacuum. The experimental results show that the intensity of the PL peak at 506 nm of Ar-implanted sapphire can be enhanced by subsequent annealing with an enhancement of nearly 20 times. The influence of thermal annealing of the Ar-implanted samples on the new 506 nm emission band was discussed.     

Temperature dependence of the luminescence of nanocrystalline CdS/Mn

The temperature dependence of the luminescence properties of nanocrystalline CdS/Mn²⁺ particles is investigated. In addition to an orange Mn²⁺ emission around 585 nm a red defect related emission around 700 nm is observed. The temperature quenching of both emissions is similar (T_q≈100 K). For the defect emission the reduction in the lifetime follows the temperature dependence of the intensity. For the Mn²⁺ emission however, the intensity decreases more rapidly than the lifetime with increasing temperature. To explain these observations a model is proposed in which the Mn²⁺ ions are excited via an intermediate state involving shallowly trapped (≈40 meV) charge carriers.     

Luminescence investigations on sulfate apatite Na6(SO4)2FCl:RE (RE=Dy, Ce or Eu) phosphors

A new phosphor in the Cl-F system doped with Dy, Ce and Eu has been reported. Characterization of this phosphor using XRD, PL and TL techniques is described. Polycrystalline Na₆(SO₄)₂FCl:Dy; Na₆(SO₄)₂FCl:Ce and Na₆(SO₄)₂FCl:Eu phosphors prepared by a solid state diffusion method have been studied for their X-ray diffraction, photoluminescence (PL) and thermoluminescence (TL)characteristics. The PL excitation and emission spectra of phosphors were obtained. Dy³⁺ emission in the host at 475 and 570 nm is observed due to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transition, respectively, whereas the PL emission spectra of Na₆(SO₄)₂FCl:Ce phosphor shows the Ce³⁺ emission at 322 nm due to 5d→4f transition of Ce³⁺ ion. In Na₆(SO₄)₂FCl:Eu lattice, Eu²⁺ as well as Eu³⁺ emissions are observed. The emission of europium ion in this compound exhibits the blue as well as red emission. The TL glow curves of the same compounds have the simple structure with a prominent peak at 150, 175 and 200 °C. TL response, fading, reusability and trapping parameters of the phosphors are also studied. The TL glow curves of γ-irradiated Na₆(SO₄)₂FCl sample show one glow peak indicating that only one set of traps is being activated within the particular temperature range each with its own value of activation energy (E) and frequency factor (s). The trapping parameters associated with the prominent glow peak are calculated using Chen’s half width method. The release of hole/electron from defect centers at the characteristic trap site initiates the luminescence process in these materials. The intensity of the TL glow peaks increases with increase of the added γ-ray dose to the samples.     

Improved color purity in nano-size Eu-doped YBO3 red phosphor

Nano-size YBO₃:Eu³⁺ phosphor has been synthesized by the co-precipitation method. X-ray diffraction (XRD) pattern confirmed the formation of hexagonal vaterite-type structures of YBO₃:Eu³⁺ nanoparticles. The transmission electron microscopy (TEM) study revealed the formation of spherical YBO₃:Eu³⁺ nanoparticles with size 20-40 nm. The photoluminescence spectra revealed that the ratio of the red emission (⁵D₀-⁷F₂) to the orange emission (⁵D₀-⁷F₁) was much higher in the synthesized nano-size YBO₃:Eu³⁺ phosphor. The improved relative intensity, i.e., higher R/O value of emission peaks, is due to a lower symmetry of crystal field around Eu³⁺ ions.     

Thermal stability and spectroscopic properties of Er-doped lead fluorogermanate glasses

The thermal characterization and spectroscopic properties of Er³⁺-doped 0.6GeO₂-(0.4-x)PbO-xPbF₂ glasses were investigated experimentally. With the replacement of PbO by PbF₂ the thermal stability of glasses is improved and the infrared fluorescence intensity at 1530 nm is increased. The Judd-Ofelt intensity parameters, radiative transition rates, and fluorescence lifetimes of the excited ⁴I_13/2 level of Er³⁺ ions were calculated from Judd-Ofelt theory. The asymmetric ligand field around Er³⁺ ions resulted from the incorporation of PbF₂ into germanate glasses, broadens the infrared emission spectra at 1530 nm. Upconversion luminescence in the investigated glasses was observed at room temperature under the excitation of 976 nm laser diode. The glass 0.6GeO₂-0.3PbO-0.1PbF₂ exhibits the maximum upconversion emission intensity, while no frequency upconversion luminescence was observed in the 0.6GeO₂-0.4PbO glass. The quadratic dependence of the green and red emissions on excitation power indicates that two-photon absorption contributes to the visible emission under the 976-nm excitation.     

Spectroscopic properties of new luminescent system based on vanadate(V) crystal doped with erbium ions

Er³⁺-doped KCaY(VO₄)₂ microcrystalline samples were synthesized using a high temperature solid-state reaction technique. Spectroscopic properties of Er³⁺: KCaY(VO₄)₂ are studied and the nature of emissions is discussed. A strong green and infrared luminescence were observed under excitation at 314 nm in the O²⁻→V⁵⁺ charge-transfer transitions and direct excitation of Er³⁺ ions at 435 nm. A strong emission lines in the blue region are due to the transitions of VO₄³⁻ ions have been observed at 77 K. The Judd-Ofelt parametrization scheme has been applied to the analysis of the room temperature absorption spectra in order to evaluate the intensity parameters, the branching ratios and the radiative lifetimes of the ⁴I_13/2, ⁴I_11/2, ⁴F_9/2 and ⁴S_3/2 emitting levels. The effective cross-section has been calculated for the ⁴I_13/2→⁴I_15/2 transition, indicating that the title compounds is a promising active medium for application in the three-level laser system. The up-conversion emission in Er³⁺: KCaY(VO₄)₂ was investigated at 300 K. The decay profiles of the Stokes and anti-Stokes emissions were measured and the mechanism of up-conversion luminescence is discussed.     

Franck-Condon factors of the torsional mode ν7 in the SVL emission of glyoxal

Drastic changes occur in the intensity pattern of the emission spectra of the 7ⁿ-levels as compared to the spectrum of the 0⁰-level. These changes are due to greatly enhanced intensity of the sidebands in the progression of the 7-vibration. This enhancement is, in a first approximation, in agreement with calculations of the Franck-Condon factors of these transitions. The additional intensity of the sidebands in the emission from the 7²-level can be explained in part by intensity borrowing from the 5¹-emission due to a coupling of the 7² and 5¹-levels. The large relative intensities of the 7₅², 7₅³, and 7₇³ emission bands remain unexplained.     

Intense red upconversion fluorescence emission in NIR-excited erbium-ytterbium doped laponite-derived phosphor

In this report the optical properties and energy-transfer frequency upconversion luminescence of Er³⁺/Yb³⁺-codoped laponite-derived powders under 975 nm infrared excitation is investigated. The 75%(laponite):25%(PbF₂) samples doped with erbium and ytterbium ions, generated high intensity red emission around 660 nm and lower intensity green emission around 525, and 545 nm. The observed emission signals were examined as a function of the excitation power and annealing temperature. The results indicate that energy-transfer, and excited-state absorption are the major upconversion excitation mechanism for the erbium excited-state red emitting level. The precursor glass samples were also heat treated at annealing temperatures of 300 °C, 400 °C, 500 °C, and 600 °C, for a 2 h period. The dependence of the visible upconversion luminescence emission upon the annealing temperature indicated the existence of an optimum temperature which leads to the generation of the most intense and spectrally pure red emission signal.     

Intense Upconversion Luminescence of Yb<Superscript>3+</Superscript>-Er<Superscript>3+</Superscript> in Li<Subscript>2</Subscript>O Content Tungsten-tellurite Glasses

The Er³⁺ -Yb³⁺ codoped in Li₂O content tungsten -tellurite (TWL) transparent glasses are synthesized and measured the absorption, Raman and upconversion luminescence (UPL) spectra. At room temperature intense green emission peak at 560 nm ( ⁴S_3/2→⁴I_15/2) and red emission peak at 670 nm ( ⁴F_9/2→⁴I_15/2) of Er³⁺ observed even at minimum 86 mW pumping power of infrared 980 nm excitation. For structure of the TWL glass, Raman spectrum result revealed that an important role of WO₃ in the formation of glass network linkage with Li₂O. Under this influence estimated lifetime of the ⁴I_11/2 of Er³⁺ was 1.89 μs and due to lower phonon energy of the glass produce strong upconversion signal. The effect of Er₂O₃ concentration on emission intensity result indicated that green emission intensity initially increase in compare to red emission. Under the 980 nm pump power variation measured the relatively increases the red emission to the green emission intensity and analyze the possible upconversion mechanism and process.     

Synthesis, characterization and optical properties of water-soluble ZnS:Mn nanoparticles

ZnS nanoparticles with Mn²⁺ doping (0.5-20%) have been prepared through a simple chemical method, namely the chemical precipitation method. The structure of the nanoparticles has been analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV-vis spectrometer. The size of the particles is found to be 3-5 nm range. Photoluminescence spectra were recorded for undoped ZnS nanoparticles using an excitation wavelength of 320 nm, exhibiting an emission peak centered at around 445 nm. However, from the Mn²⁺-doped samples, a yellow-orange emission from the Mn²⁺⁴T₁-⁶A₁ transition is observed along with the blue emission. The prepared Mn²⁺-doped sample shows efficient emission of yellow-orange light with the peak emission 580 nm with the blue emission suppressed. The maximum PL intensity is observed only at the excitation energy of 3.88 eV (320 nm). Increase in stabilizing time up to 48 h in de-ionized water yields the enhancement of emission intensity of doped (4% Mn²⁺) ZnS. The correlation made through the concentration of Mn²⁺ versus PL intensity resulted in opposite trend (mirror image) of blue and yellow emissions.     

Effect of halide ion concentration and irradiation dose dependent photostimulated luminescence investigation in the image screen phosphor CsBr1-xClx:Euy 2+

Photoluminescence(PL) characterization is carried out on CsBr_1-xCl_x:Eu_y²⁺ (x = 0.05, 0.1, 0.2, 0.3 y = 100 ppm, 200 ppm) crystals grown in vacuum with the Bridgman technique. PL studies show an increase in luminescence intensity with a decrease in bromide ion content. F(Br^–) and F(Cl^–) centers are formed due to -ray irradiation at room temperature. Photostimulated luminescence (PSL) emission is found to increase with an increase in irradiation dose from 7.5 Gy to 30 Gy at room temperature. From the results it is demonstrated that out of the different compositions studied, CsBr_0.9Cl_0.1:Eu²⁺ (200 ppm) phosphor has a linear PSL response with respect to irradiation dose.     

Probing of inversion symmetry site in Eu-doped GdPO4 by luminescence study: Concentration and annealing effect

Eu³⁺-doped gadolinium orthophosphate (GdPO₄) (Eu³⁺ at%=0, 2, 5, 7, 10, 15, 20 and 30) nanoparticles have been prepared by ethylene glycol route and subsequently heated at 500 and 900 °C. The crystallite size increases with increasing heat-treatment temperature. Luminescence study shows that magnetic dipole transition (⁵D₀→⁷F₁) is prominent over the electric dipole transition (⁵D₀→⁷F₂), which has been attributed to occupancy of inversion symmetry site by more Eu³⁺ ions in Eu³⁺-doped GdPO₄. The luminescence intensity is enhanced as heat-treatment temperature increases from 500 to 900 °C due to the improved crystallinity. Optimum luminescence is observed for 5–7 at% Eu³⁺ in GdPO₄ nanoparticles. Above this concentration, luminescence intensity decreases due to concentration quenching effect. This is supported by lifetime study.