S. Surendra Babu

Influence of the annealing temperatures on the photoluminescence of KCaBO3:Eu3+ phosphor

Novel red emitting KCaBO3:Eu phosphors have been synthesized by solid-state reaction at various temperatures. Systematic studies on annealing effects and consequent structural evolution and optical properties were investigated by various structural and photoluminescence studies. With an increase in annealing temperature (from 700 °C to 950 °C), these phosphors show a gradual change from a mixed low crystalline phase to a highly crystalline single phase, with minimized volatile impurities. Photoluminescence studies revealed that the low-temperature annealed phosphors showed distinct mixed emission composed of blue and red emissions upon UV excitation. Such dual emission is due to the coexistence of Eu3+ and Eu2+ ions, wherein the reduction of Eu3+ into Eu2+ was attributed to the presence of volatile impurities. Relatively high-temperature annealed phosphors exhibit strong red color photoluminescence due to homogeneously occupied Eu3+ ions in the host crystal charge-compensated (with K+ ions) sites of Ca2+ ions. The dominant red-to-orange emission intensity ratios and Judd–Ofelt parameters of Eu3+ ions support the strong covalent nature and site-occupation of higher asymmetry sites of K+ and Ca2+ ions. High emission life times and efficient and stable photoluminescence at different excitation wavelengths make these phosphors suitable for white LEDs and other display applications.

Investigations on luminescence performance of Sm3+ ions activated in multi-component fluoro-phosphate glasses.

Different metal oxide based fluoro-phosphate glasses doped with Sm(3+) ions are investigated using XRD, SEM with EDS, FTIR, Raman spectra, optical absorption and photo-luminescence techniques. These glass matrices have been prepared by conventional melt quenching technique. The glassy nature of the present glass matrices are confirmed by XRD profiles and SEM photographs. The composition of the glasses is checked by EDS. Based on FTIR and Raman spectra, the authors have analyzed functional groups that are present in the glass matrices. Judd-Ofelt intensity parameters, Ωλ (λ=2,4,6) have been evaluated from absorption spectra. Radiative parameters such as radiative transition probabilities (AR), radiative lifetimes (τR), integrated absorption cross sections (Σ) and branching ratios (βR) are calculated using Judd-Ofelt intensity parameters. From the photoluminescence spectra, experimental branching ratios (βexp) and stimulated emission cross-sections (σP) for all the observed emission transitions are calculated. To investigate luminescence potentiality of (4)G5/2→(6)H7/2 emission level of Sm(3+) doped different fluorophosphate glasses, experimental radiative lifetimes (τexp) are obtained from decay curve analysis for all glass matrices. Finally, these observed results are discussed and compared with the literature data.

Luminescence and optical absorption properties of Nd3+ ions in K–Mg–Al phosphate and fluorophosphate glasses

Absorption and emission properties and fluorescence lifetimes for the [Formula: see text] transition of Nd(3+) ions embedded in P(2)O(5)-K(2)O-MgO-Al(2)O(3) (PKMA)-based glasses modified with AlF(3) and BaF(2) are reported at room temperature. The observed energy levels of Nd(3+) ions in these glasses have been analysed through a semi-empirical free-ion Hamiltonian model. The spin-orbit interaction and net electrostatic interaction experienced by the Nd(3+) ions follow the trend as PKMA>PKMA+AlF(3)> PKMA+BaF(2) glasses. Judd-Ofelt analysis has been carried out on the absorption spectra of 1.0xa0mol% Nd(3+)-doped glasses to predict the radiative properties for the fluorescent levels of the Nd(3+) ion. Branching ratios and stimulated emission cross-sections show that the [Formula: see text] transition of the glasses under investigation has the potential for laser applications. The Inokuti-Hirayama model has been applied to investigate the non-radiative relaxation of the Nd(3+) ion emitting state, (4)F(3/2). Based on the decay curve analysis, concentration quenching of the (4)F(3/2) emission has been attributed to a cross-relaxation process between the Nd(3+) ions.

Photoluminescence from the 5D0 level of Eu3+ ions in a phosphate glass under pressure

The pressure dependence of the luminescence from [Formula: see text] transitions of Eu(3+) ions in 58.5P(2)O(5)-9Al(2)O(3)-14.5BaO-17K(2)O-1Eu(2)O(3) glass has been investigated up to 38.3xa0GPa at room temperature. The relative luminescence intensity ratio of [Formula: see text] to [Formula: see text] transitions of the Eu(3+) ions is found to decrease with increasing pressure, indicating a lowering of the asymmetry around the Eu(3+) ions with pressure. The [Formula: see text] transitions exhibit pressure-induced red shifts of different magnitude, which suggests a decrease in Slater parameters (F(k)) and in the spin-orbit coupling parameters (ζ) for the Eu(3+) ions. Stark components of the (7)F(1) level have been used to evaluate the crystal-field (CF) parameters B(20) and B(22), which are in turn used to estimate the CF strength experienced by the Eu(3+) ions in the glass. The observed increase in the CF strength parameter is found to have an almost cubic dependence on pressure. Luminescence decay curves for the [Formula: see text] transition are found to be single exponential over the entire pressure range studied. The lifetime did not change under pressure up to 5xa0GPa, although a significant change in the CF strength is noticed in this pressure range. The reduction of lifetime observed at pressures above 5xa0GPa could be partially due to an increase of pressure-induced defect centres. Such a process can then explain the hysteresis observed in the variation of lifetime and crystal-field strength on the release of pressure.

A fluorescence study of Tb3+ doped tellurite glass under pressure

Fluorescence spectra and decay curves for the transition of Tb3+ ions in 59TeO2?20ZnO?20LiF?1Tb4O7?(TZLFTb) glass have been measured and analysed as a function of pressure up to 14.9?GPa at room temperature. In this pressure range, the red shift for the band positions of ,7F4 and 7F5 is found to be?3.2, 3.2 and 2.2?cm?1?GPa?1, respectively, which could be attributed to an expansion of the 4f?electron wavefunctions with increasing covalency. There is also a considerable pressure effect on the magnitude of the crystal-field splittings observed in the 7F4 and 7F5 transitions, which increases with pressure because of Coulomb interactions between the 4f electrons and their ligands. In addition, the decay curve is found to be perfectly single exponential at ambient pressure, and turns into a non-exponential with increasing pressure. The non-exponential decay curves at higher pressures are well fitted to the Inokuti?Hirayama model for S = 6, which indicates that the energy transfer between the donor and acceptor is of dipole?dipole nature. The decrease in the lifetime with increasing pressure is caused by an increase in the electronic transition probabilities, which is a result of the enhanced crystal-field strength around the Tb3+ ions. The results obtained after release of pressure show that local environment changes of the Tb3+ ions are reversible.

Compositional-dependent properties of Pr3+-doped multicomponent fluoro-phosphate glasses for visible applications: a photoluminescence study

Five fluoro-phosphate (FP) glasses of different compositions, 49.5P2O5–10AlF3–10BaF2–10SrF2–10PbO–10M (Mxa0=xa0Li2O, Na2O, K2O, ZnO, and Bi2O3), doped with 0.5xa0mol% praseodymium were prepared by melt quenching technique. For these glass matrices, structural, thermal, dielectric, electrical, and optical properties have been studied. The structures are characterized by XRD, Fourier transform infrared, Raman spectroscopy, and solid-state 31P and 27Al magic angle spinning nuclear magnetic resonance techniques. The chemical and electronic states of these glass materials are characterized by X-ray photoelectron spectroscopy. The thermal stability for the host glass matrix is estimated from differential scanning calorimetry technique. From the impedance spectroscopy, various parameters, viz. electrical conductivity, dielectric constant (ε′), and dielectric losses (tan δ), at various frequencies and temperatures have been measured. X-ray absorption near-edge spectroscopy was used to study the electronic structure of praseodymium in the host glass matrices. By analyzing the absorption spectra with Judd–Ofelt theory, three intensity parameters (Ωλ, λxa0=xa02, 4, 6) are obtained. In turn, these parameters are used to calculate radiative properties such as emission probabilities (AR), radiative lifetimes (τR), and integrated absorption cross sections (Σ) of different Pr3+ transitions. Luminescence parameters such as stimulated emission cross sections (σp) and branching ratios (βexp) have been studied through photoluminescence spectra. Further, decay time constants are estimated from the decay profiles of Pr3+-doped different FP glasses.

Optical properties and spectroscopic study of different modifier based Pr3 +:LiFB glasses as optical amplifiers

In this paper, we report the preparation and optical characterization of Pr(3+) doped lithium fluoro borate (LiFB) glasses for six different chemical compositions of Li2B4O7-BaF2-NaF-MO (where M=Mg, Ca, Cd and Pb), Li2B4O7-BaF2-NaF-MgO-CaO and Li2B4O7-BaF2-NaF-CdO-PbO. The structural and optical properties of these glasses were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), optical absorption and photoluminescence techniques. The optical absorption spectra of Pr(3+) ions in LiFB glasses have been recorded in the UV-VIS-NIR region. The optical absorption data are used to calculate various spectroscopic parameters such as Racah (E(1), E(2), E(3)) and spin-orbit interaction (ξ4f) parameters. Judd-Ofelt (J-O) (Ωλ where λ=2, 4 and 6) intensity parameters were determined by applying J-O theory, which in turn used to calculate the radiative properties such as radiative transition probabilities (A), radiative lifetimes (τR), integrated absorption cross-sections (Σ) and branching ratios (βr) for all emission levels of Pr(3+) ion in different LiFB glass matrices. By using the J-O theory and luminescence parameters, stimulated emission cross sections (σp) of prominent transitions, (3)P0→(3)H4 and (1)D2→(3)H4 of Pr(3+) ion in all LiFB glasses were calculated. (3)P0→(3)H4 possesses higher branching ratios and stimulated emission cross-sections for the Pr(3+):LiFB(Mg-Ca) glass, which can be used as a best laser excitation. The optical gain parameter (σpxτR) was noticed higher in Pr(3+):LiFB(Mg-Ca) and Pr(3+):LiFB(Cd-Pb) glasses for the transition (3)P0→(3)H4 transition, and these glasses have potential for optical amplification at 488 nm wavelength.

Luminescence performance of Eu3+-doped lead-free zinc phosphate glasses for red emission

In this study, the luminescence performance of zinc phosphate glasses containing Eu3+ ion with the chemical compositions (60–x)NH4H2PO4-20ZnO-10BaF2-10NaF–x Eu2O3 (where x = 0.2, 0.5, 1.0 and 1.5 mol%) has been studied. These glasses were characterized by several spectroscopic techniques at room temperature. All the glasses showed relatively broad fluorescence excitation and luminescence spectra. Luminescence spectra of these glasses exhibit characteristic emission of Eu3+ ion with an intense and most prominent red emission (614 nm), which is attributed to 5D0 → 7F2 transition. Judd-Ofelt (Ω2, Ω4) parameters have been evaluated from the luminescence intensity ratios of 5D0 → 7FJ (where J = 2 and 4) to 5D0 → 7F1 transition. Using J-O parameters and excitation spectra, the radiative parameters are calculated for different Eu3+-doped glasses. Effect of γ-irradiation at fixed dose has been studied for all the Eu3+-doped glass matrices. The lifetimes of the excited level, 5D0, have been measured experimentally through decay profiles. The colour chromaticity coordinates are calculated and represented in the chromaticity diagram for Eu3+-doped zinc phosphate glasses for all concentrations.

Optical Amplifiers from Rare-Earth Co-Doped Glass Waveguides

Optical amplifiers are of potential use in wide variety of optoelectronic and optical communication applications, particularly for Wavelength Division Multiplexing (WDM) to increase the number of channels and transmission capacity in optical network systems. For efficient performance of WDM systems, essential requirements are larger bandwidth, higher output power and flat gain over entire region of operation. Recent research is focused on design and development of fiber/MEMS-compatible optical amplifiers. Some examples of such sources are semiconductor quantum dot light-emitting diodes, super-luminescent diodes, Erbium doped fibre amplifier (EDFA, 1530-1625nm), Erbium doped planar amplifier (EDWAs), Fibre Raman amplifier, Thulium doped fibre amplifier (1460-1510nm). However, for many applications covering the total telecommunication window (1260-1700nm) is highly desirable and as such it is not yet realized. Typical attenuation spectrum for glassy host is shown in Figure 1. Specially the low loss region extending from 1450 to 1600 nm, deemed the 3rd telecommunication window, emerged as the most practical for long haul telecommunication systems. This window has been split into several distinct bands: Shortband (S-band), Centre-band (C-band) and Long-band (L-band). With several generations of development, the transmission rates have increased dramatically so that several Terabits per second data can be transmitted over a single optical fiber at carrier wavelengths near 1550 nm, a principal optical communication window in which propagation losses are minimum. EDFAs are attractive to WDM technology to compensate the losses introduced by WDM systems and hence has grown as a key to upgrade the transmission capacity of the present fiber links. EDFAs are widely used in long-haul fiber optic networks where the fiber losses are limited to 0.2 dB/km, is compensated periodically by placing EDFAs in the transmission link with spacing of up to 100 km. EDFAs make use of trivalent erbium (Er3+) ions to provide the optical amplification at wavelengths near 1550 nm, the long wavelength window dominantly used in optic networks since the fiber losses are found minimum around this wavelength. Light from an external energy source at a wavelength of 980 nm or 1450 nm, coupled along with the information signal, and is passed through the EDFA to excite the Er3+ ions in order to produce the optical amplification through stimulated emission of photons at the signal wavelength. Er3+ doped waveguides (EDWA) have

Concentration-dependent studies of Nd3+-doped zinc phosphate glasses for NIR photoluminescence at 1.05 μm

Nd3+ -doped lead-free zinc phosphate glasses with the chemical compositions (60-x) NH4 H2 PO4 xa0+xa020ZnOxa0+xa010BaF2 xa0+xa010NaFxa0+xa0xNd2 O3 (where xxa0=xa00.5, 1.0, 1.5, 2.0 and 2.5xa0mol%) were prepared using a melt quenching technique. Vibrational bands were assigned and clearly elucidated by Raman spectral profiles for all the glass samples. Judd-Ofelt (J-O) intensity parameters (Ωλ : λxa0=xa02, 4, 6) were obtained from the spectral intensities of different absorption bands of Nd3+ ions. Radiative properties such as radiative transition probabilities (AR ), radiative lifetimes (τR ) and branching ratios (βR ) for different excited states were calculated using J-O parameters. The near infrared (NIR) photoluminescence spectra exhibited three emission bands (4 F3/2 level to 4 I13/2 , 4 I11/2 and 4 I9/2 states) for all the concentrations of Nd3+ ions. Various luminescence properties were studied by varying the Nd3+ concentration for the three spectral profiles. Fluorescence decay curves of the 4 F3/2 level were recorded. The energy transfer mechanism that leads to quenching of the 4 F3/2 state lifetimes was discussed at higher concentration of Nd3+ ions. These glasses are suggested as suitable hosts to produce efficient lasing action in NIR region at 1.05xa0μm.