On the Luminescence of Ce<Superscript>3+</Superscript>, Eu<Superscript>3+</Superscript>, and Tb<Superscript>3+</Superscript> in Novel Borate LiSr<Subscript>4</Subscript>(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>

This paper reports on the photoluminescence (PL) and time-resolved properties of Ce³⁺, Eu³⁺, and Tb³⁺ in novel LiSr₄(BO₃)₃ powder phosphors. Ce³⁺ shows an emission band peaking at 420 nm under 350-nm UV excitation. Energy transfer from Ce³⁺ to Mn²⁺ takes place in the co-doped samples. Eu³⁺ shows red emission under near UV excitation. LiSr₄(BO₃)₃:Eu³⁺ phosphor could be a suitable candidate for phosphor-converted solid state lighting. The luminescence lifetime is 2.13 ms for Eu³⁺ in LiSr₄(BO₃)₃:0.001Eu³⁺. As Eu³⁺ concentration increasing, the decay curves deviate from exponential behavior. Tb³⁺ shows the strongest ⁵D₄→⁷ F₅ emission line at 540 nm. Decay curves of ⁵D₄→⁷ F₅ and ⁵D₃→⁷ F₅ emission with different Tb³⁺ concentrations were also measured. Cross-relaxation process is discussed based on the decay curves.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

Spectrofluorimetric Assessment of Hydrochlorothiazide Using Optical Sensor Nano-Composite Terbium Ion Doped in Sol-Gel Matrix

A new, simple, sensitive and selective spectrofluorimetric method for the determination of Hydrochlorothiazide was developed in acetonitrile at pH 6.2. The Hydrochlorothiazide can remarkably enhance the luminescence intensity of the Tb³⁺ ion doped in sol–gel matrix at λ_ex = 370 nm. The intensity of the emission band of Tb³⁺ ion doped in sol–gel matrix was increased due to the energy transfer from the triplet excited state of Hydrochlorothiazide to (⁵D₄) excited energy state of Tb³ ion. The enhancement of the emission band of Tb³⁺ ion doped in sol–gel matrix at (⁵D₄→⁷ F₅) 545 nm was directly proportion to the concentration of Hydrochlorothiazide with a dynamic ranges of 5.0 × 10⁻¹⁰—5.0 × 10⁻⁶ mol L⁻¹ and detection limit of 2.2 × 10⁻¹¹ mol L⁻¹.     

Thermally and photostimulated recombination processes in PbWO4 crystals at low temperatures

We have studied thermally and photostimulated recombination processes in PbWO₄ crystals in the temperature interval 90–295 K. We have shown that after x-ray excitation of the crystal at 90 K, the thermally stimulated luminescence curve shows a relatively intense peak at 110 K and weak peaks at about 173, 191, and 232 K. Exposure of the PbWO₄ crystal to IR radiation after excitation by x-ray photons leads to the appearance of photostimulated flash luminescence, a significant decrease in the intensity of the 110 K peak, and a shift of that peak to the 116 K region. But long-wavelength illumination has less of an effect on the intensity and position of the higher temperature peaks. It is assumed that F⁻ centers are formed in the PbWO₄ crystal at 90 K during x-ray exposure. The thermal light sum released by IR illumination in the temperature region 90–150 K has a maximum at ≈108 K. The nature of this maximum is connected with the complex centers [Pb³⁺ + (WO_3-F⁻)]. Optical and thermal degradation of these centers leads to the appearance of emission in the green region of the localized exciton spectrum.     

Terbium Sensitized Luminescence for the Determination of Ketoprofen in Pharmaceutical Formulations

This paper explores an ultra-sensitive luminescence method for the determination of Ketoprofen (KP) in pharmaceutical formulations. The technique is indirect and exploits the luminescence enhancement of terbium (Tb³⁺) by complexation with KP (Tb³⁺–KP), which was monitored at respective excitation and emission wavelengths of λ _ex = 258 nm and λ _em = 549 nm. The effect of varying the Tb³⁺ concentration and using multiple solvents was examined to determine optimal experimental conditions. Maximum sensitization was accomplished in the presence of methanol where the most favourable condition for the formation of the complex was recorded at a level of 1.0 × 10⁻⁵ M of Tb³⁺. Under these optimum experimental conditions, linear calibration curve was obtained in the range of 2.8 × 10⁻⁷–3.1 × 10⁻⁶ M with a detection limit of 8.7 × 10⁻⁸ M. The technique was validated with ‘working’ reference standards and produced relative standard deviations < 2% indicating that the reproducibility was highly acceptable. The proposed method was successfully applied to assays of KP in pharmaceutical formulations with average recoveries of 92–98%. The results were found to be in good agreement with those obtained by HPLC. The method is highly suited for general applications of this nature.     

Influence of magnetic ordering on electronic structure of Tb<Superscript>3+</Superscript> ion in TbFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> crystal

Optical absorption spectra of trigonal crystal TbFe₃(BO₃)₄ have been studied in the region of ⁷F₆ → ⁵D₄ transition in Tb³⁺ ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb³⁺ excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice, have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be due to the abrupt change of equilibrium geometry of the local Tb³⁺ ion environment only in the excited state of the Tb³⁺ ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb³⁺ local environment in the excited states. The crystal field splitting components have been identified. In particular, it has been shown that the ground state (in D ₃ symmetry approximation) consists of two close singlet states of A ₁ and A ₂ type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of the excited electronic states relative to that of the ground state have been experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines has been observed in the vicinity of the TbFe₃(BO₃)₄ structural phase transition. The temperature interval of coexistence of the phases is about 3 K.     

Luminescence properties of phosphors based on Tb<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> (TbAG) terbium-aluminum garnet

The processes of excitation energy transfer in phosphors based on single-crystal Tb₃Al₅O₁₂:Ce (TbAG:Ce) and Tb₃Al₅O₁₂:Ce,Eu (TbAG:Ce,Eu) garnet films have been investigated. These films are considered to be promising materials for screens for X-ray images and luminescence converters of blue LED radiation. The conditions for excitation energy transfer from the matrix (Tb³⁺ cations) to Ce³⁺ and Eu³⁺ ions in TbAG:Ce and TbAG:Ce,Eu phosphors have been analyzed in detail. It is established that a cascade process of excitation energy transfer from Tb³⁺ ions to Ce³⁺ and Eu³⁺ ions and from Ce³⁺ ions to Eu³⁺ ions is implemented in TbAG:Ce,Eu via dipole-dipole interaction and through the Tb³⁺ cation sublattice.     

Optical spectra and excited state relaxation dynamics of Sm<Superscript>3+</Superscript> in Gd<Subscript>2</Subscript>SiO<Subscript>5</Subscript> single crystal

Single crystals of gadolinium orthosilicate Gd₂SiO₅ containing 0.5 at% and 5 at% of Sm³⁺ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the ⁴G_5/2→⁶H_J (J=5/2–11/2) transitions of Sm³⁺ in the visible and near infrared region the ⁴G_5/2 →⁶H_7/2 one has the highest intensity with a peak emission cross section of 3.54×10⁻²¹ cm² at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd₂SiO₅:0.5 at% Sm³⁺ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the ⁴G_5/2 radiative lifetime τ _rad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd₂SiO₅:5 at% Sm³⁺ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm³⁺–Sm³⁺ energy transfer C _da=1.264×10⁻⁵² cm⁶×s⁻¹.     

The Role of the Eu<Superscript>3+</Superscript> Concentration on the SrMoO<Subscript>4</Subscript>:Eu Phosphor Properties: Synthesis,Characterization and Photophysical Studies

SrMoO₄ doped with rare earth are still scarce nowadays and have attracted great attention due to their applications as scintillating materials in electro-optical like solid-state lasers and optical fibers, for instance. In this work Sr_1−xEu_xMoO₄ powders, where x = 0.01; 0.03 and 0.05, were synthesized by Complex Polymerization (CP) Method. The structural and optical properties of the SrMoO₄:Eu³⁺ were analyzed by powder X-ray diffraction patterns, Fourier Transform Infra-Red (FTIR), Raman Spectroscopy, and through Photoluminescent Measurements (PL). Only a crystalline scheelite-type phase was obtained when the powders were heat-treated at 800 °C for 2 h, 2θ = 27.8° (100% peak). The excitation spectra of the SrMoO₄:Eu³⁺ (λ_Em. = 614 nm) presented the characteristic band of the Eu^3 + 5L₆ transition at 394 nm and a broad band at around 288 nm ascribed to the charge-transfer from the O (2p) state to the Mo (4d) one in the SrMoO₄ matrix. The emission spectra of the SrMoO₄:Eu³⁺ powders (λ_Exc. = 394 and 288 nm) show the group of sharp emission bands among 523–554 nm and 578–699 nm, assigned to the ⁵D₁→⁷F_{0,1and 2} and ⁵D₀→⁷F_{0,1,2,3 and 4}, respectively. The band related to the ⁵D₀→⁷F₀ transition indicates the presence of Eu³⁺ site without inversion center. This hypothesis is strengthened by the fact that the band referent to the ⁵D₀→⁷F₂ transition is the most intense in the emission spectra.     

Intense White Luminescence from Combustion Synthesized Ca<Subscript>12</Subscript>Al<Subscript>14</Subscript>O<Subscript>33</Subscript>: Yb<Superscript>3+</Superscript>/Yb<Superscript>2+</Superscript> Single Phase Phosphor

The Ca₁₂Al₁₄O₃₃: Yb³⁺/Yb²⁺ single phase nano-phosphor has been synthesized through combustion route and its luminescence and lifetime studies have been carried out up to 20 K using 976 and 266 nm excitations. The samples heated in open atmosphere have shown the presence of Yb in Yb³⁺ and Yb²⁺ states. The 976 nm excitation results a cooperative upconversion emission at 486 nm due to the Yb³⁺ state and a broad band in the blue region and has been assigned to arise from the defect centers. The 266 nm excitation on the other hand results a broad emission band even from as-synthesized phosphor without doping of Yb, the width of which increases in presence of Yb due to the emission from Yb²⁺ ions formed in heated samples. The white emission covers almost whole visible region with bandwidth 190 nm. The ions in Yb²⁺ state has been found to increase with the increase in heating temperature up to 1,273 K. A back conversion of Yb²⁺ to Yb³⁺ has been observed for higher temperatures. Effect of boric and phosphoric acids as flux on the emission properties of Yb³⁺ and Yb²⁺ states have been examined and discussed. Quantum yield of emission has also been determined for different samples.     

PbWO<Subscript>4</Subscript> crystal for laser energy accumulation and transformation

The picosecond interband two-photon laser excitation of PbWO₄ crystals at a temperature of 10 K leads to electronic excitation energy accumulation, which results in almost 100% induced absorption in the 450–750 nm spectral range. The relaxation time of this induced absorption exceeds 100 min. The electronic excitation energy accumulated in the PbWO₄ crystal at T = 10 K excites the intrinsic luminescence with a decay time longer than 45 min. The decay kinetics and the spectra of the intrinsic luminescence of the PbWO₄ crystal at a temperature of 10 K were measured under two-photon and single-photon excitation. The luminescence under two-photon and single-photon excitation revealed a difference in the structure of the spectra.     

Correlation of photoluminescence of (La,Ln) PO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> (Ln = Gd and Y) phosphors with their crystal structures

Eu³⁺-doped (La, Ln) PO₄ (Ln = Gd and Y) phosphors were prepared by a facile co-precipitation method. Their structures and luminescent properties under UV excitation were investigated. Structural characterization of the nanostructured luminescence material was carried out with X-ray powder diffraction analysis. Scanning electron microscopy was carried out to understand the surface morphological features and grain sizes with 50–100 nm. It is found that (La, Gd) PO₄:Eu³⁺ phosphors have the same crystal structure as LaPO₄:Eu³⁺, which is monoclinic with a little different lattice parameters. In the case of (La, Y) PO₄:Eu³⁺ phosphors, however, the gradual change from monoclinic to tetragonal structure of host lattice was observed, as the amount of Y ion increased. From the photoluminescence spectra for (La, Ln) PO₄:Eu³⁺ (Ln = Gd and Y), the emission transition ⁵D₀ → ⁷F₁ has been found to be more prominent over the normal red emission transition ⁵D₀ → ⁷F₂. Furthermore, the size influence on the products was discussed. It was observed that the spectral features possess sharp and bright emission for potential applications on the monitors of the television and some other related electronic systems, in observing the images in orange–red color.     

Time-Resolved Vacuum Ultraviolet Spectroscopy of Er<Superscript>3+</Superscript> Ions in the SrF<Subscript>2</Subscript> Crystal

The photoluminescence and photoexcitation spectra as well as the luminescence decay kinetics of Er³⁺ ions in the visible ultraviolet and vacuum ultraviolet (VUV) regions have been studied by the method of low-temperature, time-resolved VUV-spectroscopy on excitation by synchrotron radiation. In the VUV spectral region of the luminescence of SrF₂:1% Er³⁺, the 146.5-nm band with a time of decay of less than 0.6 nsec was revealed together with the well-known emission band at 164.3 nm (decay constant in the microsecond range). Its possible nature is discussed. The specific features of the formation of photoexcitation spectra of the f-f and f-d transitions in the Er³⁺ ion are considered. Competition between the processes of excitation of f-f and d-f luminescence has been revealed. It manifests itself in the inverse relationship of their photoexcitation spectra in a range of energies of incident photons that are close to the position of the 4fⁿ⁻¹5d configuration levels. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 519–523, July–August, 2005.     

Optical absorption spectra and magnetic phase transitions in TbFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Optical absorption spectra of the trigonal crystal of TbFe₃(BO₃)₄ in the vicinity of the ⁷F₆ → ⁵D₄ transition in a Tb³⁺ ion were studied as a function of temperature (2–70 K) and magnetic field strength (0–60 kOe) at 2 K. The splitting of the excited states of Tb³⁺ due to both the magnetic ordering of iron and an external magnetic field was determined. Abrupt splitting of the absorption lines of Tb³⁺ at temperature T_N of the magnetic ordering of the subsystem of iron was revealed, suggesting that the nature of such splitting is not entirely magnetic.     

Resonant processes causing photon multiplication in CaSO4:Tb3+

The emission spectra of single and polyterbium centers have been measured at the excitation of CaSO₄:Tb³⁺ phosphors with different charge compensators (Na⁺, calcium vacancies, etc.) by 3.8–35 eV photons or 5 and 300 keV electrons at 6–300 K. The possible mechanisms providing quantum yield above unity for green (⁵D₄ → ⁷F_J) and blue emission (⁵D₃ → ⁷F_J) of Tb³⁺ at the direct intracenter excitation, excitation of oxyanions or creation of hot (nonrelaxed) electrons and holes have been discussed. On the basis of thermally stimulated luminescence at 6–600 K, the peculiarities of the hopping diffusion of relaxed electrons and holes and their tentative low-temperature self-trapping have been considered.     

Dynamics of two-photon picosecond absorption in ZnWO<Subscript>4</Subscript> and PbWO<Subscript>4</Subscript> crystals

A method has been proposed to analyze the dynamics of interband two-photon absorption in a nonlinear medium excited by a sequence of picosecond laser pulses of variable intensity and continuous probe radiation. Induced absorption leading both to hysteresis in the dependence of the absorption on the intensity of laser pump radiation and to the opacity of crystals at the pump wavelength has been revealed in initially transparent ZnWO₄ and PbWO₄ crystals irradiated by a train of 523.5-nm pulses with a duration of 20 ps at pump intensities of 5 to 140 GW/cm². The kinetics of an increase in absorption and its subsequent relaxation at a 523.5-nm picosecond excitation of the crystals have been measured with continuous 633-nm probe radiation. An exponential component of the increase in absorption with the time constant τ = 2−3.5 and 8–9.5 μs depending on the direction of the linear polarization of pump radiation has been revealed at 300 K in ZnWO₄ and PbWO₄ crystals, respectively. The absorption relaxation kinetics in the crystals are complicated and approach an exponential at a late stage with the constant τ = 40−130 and 12–80 ms for the ZnWO₄ and PbWO₄ crystals, respectively.     

Luminescence and energy transfer mechanism in Eu<Superscript>3+</Superscript>/Tb<Superscript>3+</Superscript>-co-doped ZrO<Subscript>2</Subscript> nanocrystal rods

Nanocrystal rods of Eu³⁺/Tb³⁺-co-doped ZrO₂ were synthesized using a simple chemical precipitation technique. Both ions were successfully doped into the Zr⁴⁺ ion site in a mixed structure containing both monoclinic and tetragonal phases. The Eu³⁺ or Tb³⁺ singly doped zirconia produced red and green luminescence which are characteristics of Eu³⁺ and Tb³⁺ ions, respectively. The co-doped zirconia samples produced blue emission from defect states transitions in the host ZrO₂, red and green luminescence from dopant ions giving cool to warm white light emissions. The phosphors were efficiently excited by ultraviolet and near-ultraviolet/blue radiations giving white and red light, respectively. The decay lifetime was found to increase with increasing donor ion concentration contrary to conventional observations reported by previous researchers. Weak quadrupole–quatdrupole multipolar process was responsible for energy transfer from Tb³⁺ (donor) ion to Eu³⁺ ion. No energy back-transfer from Eu³⁺ to Tb³⁺ ion was observed from the excitation spectra. Temperature-dependent photoluminescence shows the presence of defects at low temperature, but these defects vanished at room temperature and beyond. The Eu³⁺/Tb³⁺-co-doped ZrO₂ nanocrystal rod is a potential phosphor for white light application using UV as an excitation source. Thermoluminescence measurements show that the inclusion of Tb³⁺ ion increases trap depths in the host zirconia.     

Spectrofluorimetric Assessment of Metoclopramide Hydrochloride Using Terbium Doped in PMMA Matrix Optical Sensor

A new, simple and accurate spectrofluorimetric method for the determination of metoclopramide hydrochloride was developed. The metoclopramide hydrochloride can remarkably enhance the luminescence intensity of the Tb³⁺ ion doped in PMMA matrix at λ_ex = 360 nm in methanol at pH 6.9. The intensity of the emission band at 545 nm of Tb³⁺ ion doped in PMMA matrix is increased due to the energy transfer from metoclopramide hydrochloride to Tb³⁺ in the excited stated. The effect of different parameters, e.g., pH, temperature, Tb³⁺ concentration, foreign ions that control the fluorescence intensity of the produced ion associate was critically investigated. The calibration curve of the emission intensity at 545 nm shows linear response of metoclopramide over a concentration range of 5 × 10⁻⁵–5.0 × 10⁻⁸ M with detection limit of 8.7 × 10⁻¹⁰ M. The method was used successfully for the determination of metoclopramide in pharmaceutical preparations and human serum. The average recovery of 99.48% with standard deviation of 0.32% and 96.98% with standard deviation of 0.4%, of pharmaceutical preparations and human serum respectively, were obtained which compared will with the results obtained from standard LC method of average recovery 99.04% and standard deviation of 0.6% and average recovery of 98.19% with standard deviation of 0.6% of pharmaceutical preparations and human serum, respectively.     

Green emission of Ca<Subscript>3</Subscript>La<Subscript>3(1-x)</Subscript>Tb<Subscript>3x</Subscript>(BO<Subscript>3</Subscript>)<Subscript>5</Subscript> under VUV-UV excitation

A series of phosphors Ca₃La_3(1-x)Tb_3x(BO₃)₅ were synthesized by using a high-temperature solid-state reaction technique, and their VUV-vis luminescence properties were investigated. Strong host-related absorption is observed in the VUV region, and the f–d transitions of Tb³⁺ in the host lattice are assigned and discussed. The influence of both the doping concentration and the temperature on the spectroscopic properties that include the relative emission intensity and the decay time is investigated. PACS 61.72.Ww; 78.55.-m; 78.47.+p     

Recombination luminescence of CaSO4:Tb3+ and CaSO4:Gd3+phosphors

A comparative study of the excitation of luminescence by VUV radiation as well as of thermally and photostimulated luminescence has been carried out for CaSO₄:Tb³⁺ and CaSO₄:Gd³⁺ phosphors, where Na⁺ or F⁻ ions are used for charge compensation. The distinction in hole processes for the phosphors with Na⁺ or F⁻ compensators is determined by the differing thermal stability of the holes localized at/near Tb³⁺Na⁺ and Gd³⁺Na⁺ (up to 100–160 K) or at/near Tb³⁺F⁻ V _Ca and Gd³⁺F⁻ V _Ca centers involving also a cation vacancy (up to 400–550 K). Tunnel luminescence in the pairs of localized electrons and holes nearby Tb³⁺ or Gd³⁺ has been detected. The mechanisms of electron-hole, hole-electron and tunnel recombination luminescence as well as a subsequent released energy transfer to RE³⁺ ions are considered.