K. Linganna

Optical properties of Er 3+ -doped K-Ca-Al fluorophosphate glasses for optical amplification at 1.53 μm

Er3+-doped K-Ca-Al fluorophosphate glasses were prepared by melt quenching technique and their thermal and optical properties were studied. The thermal stability factor was obtained to be 131 °C. The gain bandwidth, lifetime and quantum efficiency of the 4I13/2→4I15/2 transition were found to be 96.14 × 10−27 cm3, 5.41 ms and 61%, respectively for 1.0 mol% Er2O3-doped glass. The quenching concentration has been evaluated (Q = 2.30 mol%) and found to be higher compared to other reported glasses. These results clearly indicate that present glasses are suitable for laser as well as optical amplifiers in the 1.53 μm region.

Effect of heat treatment of optical fiber incorporated with Au nano-particles on surface plasmon resonance

To improve the sensitivity of the surface plasmon resonance (SPR) sensor based on the specialty optical fiber incorporated with Au nano-particles (NPs) in the cladding region, the effect of heat treatment (800 °C - 1000 °C) of the fiber on sensing capability of refractive index (n = 1.418 - 1.448) was investigated. The SPR appeared at a particular wavelength around 390 nm for the corresponding refractive indices regardless of the heat treatment temperature and the SPR wavelength increased with the increase of the index. The SPR sensitivity was found to increase with the increase of heat treatment temperature, 178 nm/RIU, 299 nm/RIU, and 945 nm/RIU at 800 °C, 900 °C, and 1000 °C for an hour, respectively. On the other hand, the SPR absorption intensity decreased with the increase of heat treatment temperature due to the increase of the propagation loss of the incident light and the SPR band became spread due to the increase of the size distribution of the Au NPs at the various refractive indices.

Infrared-to-Visible Light Conversion in Er(3+) -Yb(3+) :Lu3 Ga5 O12 Nanogarnets.

Er(3+) -Yb(3+) co-doped Lu3 Ga5 O12 nanogarnets were prepared and characterized; their structural and luminescence properties were determined as a function of the Yb(3+) concentration. The morphology of the nanogarnets was studied by HRTEM. Under 488 nm excitation, the nanogarnets emit green, red, and near-infrared light. The decay curves for the ((4) S3/2 , (2) H11/2 ) and (4) F9/2 levels of the Er(3+) ions exhibit a non-exponential nature under resonant laser excitation and their effective lifetimes are found to decrease with an increase in the Yb(3+) concentration from 1.0 to 10.0 mol %. The non-exponential decay curves are well fitted to the Inokuti-Hirayama model for S=8, indicating that the mechanism of interaction for energy transfer between the optically active ions is of dipole-quadrupole type. Upon 976 nm laser excitation, an intense green upconverted emission is clearly observed by the naked eyes. A significant enhancement of the red-to-green intensity ratio of Er(3+) ions was observed with an increase in Yb(3+) concentration. The power dependence and the dynamics of the upconverted emission confirm the existence of two-photon upconversion processes for the green and red emissions.

Role of Dy3+ → Sm3+ energy transfer in the tuning of warm to cold white light emission in Dy3+/Sm3+ co-doped Lu3Ga5O12 nano-garnets

Nano-crystalline lutetium gallium garnets co-doped with Dy3+ and Sm3+ ions have been synthesized via a sol–gel method and their structural, morphological and luminescence properties have been characterized. All the garnets have been crystallized in a single phase of cubic structure, with an average size of 40 nm, with coral shape morphology. Under different excitation wavelengths, the nano-garnets exhibit the strong yellow and blue emissions of Dy3+ ions, as well as the orange and red emissions of Sm3+ ions. In Dy3+/Sm3+ co-doped Lu3Ga5O12 nano-garnets, white light emission has been tuned from warm to cool by varying the concentration of Sm3+ ions, as well as the excitation wavelength. The color coordinates for 2 mol% Dy3+/10 mol% Sm3+ co-doped nano-garnets have been found to be (0.317, 0.321), quite close to ideal white light, with a correlated color temperature of 6322 K under 351 nm excitation. Moreover, decay times, multipolar interactions, and energy transfer parameters for excited states of Dy3+ and Sm3+ ions in co-doped nano-garnets have been evaluated to derive the relationship between the doping concentration and luminescence properties. These results reveal that the studied nano-garnets could be a potential candidate for white light emitting device applications.

UV Photoluminescence of Alumino-Germano-Silicate Glass Optical Fiber Incorporated with Gd2O3 Nano-Particles Upon Illumination of Xenon-Lamp

Alumino-germano-silicate glass optical fiber incorporated with Gd2O3 nano-particles (NPs) was developed by using the modified chemical vapor deposition and the drawing process. The formation of spherical Gd2O3 NPs in the fiber core with average diameter of 10.8 nm was confirmed by the TEM. The distinct absorption peaks in the fiber preform appearing in the UV region at 205, 247, 253, 274, and 312 nm were due to the incorporated Gd2O3 NPs via reorganization of the seven 4f electrons into various multiplets of Gd ions. In the case of the optical fiber obtained by drawing of the preform at high temperature about 2150 °C, absorption peaks due to Gd2O3 NPs were found to appear at 383 and 455 nm, which were red-shifted from 274 and 312 nm of the preform, respectively, and it may be due to increase in the size of Gd2O3 NPs after the drawing process. To investigate the photoluminescence (PL) property for UV sensor applications, the PL of the fiber was obtained by illumination of the Xenon-lamp. A PL band appeared in the wavelength band from 370 nm to 450 nm, centering at about 400 nm, which can be attributed to the presence of Gd2O3 NPs embedded in the fiber core. It was also found that the PL intensity at 400 nm showed linear dependence with the excitation power from 0 to 400 W.

Temperature and Vibration Dependence of the Faraday Effect of Gd2O3 NPs-Doped Alumino-Silicate Glass Optical Fiber

All-optical fiber magnetic field sensor based on the Gd2O3 nano-particles (NPs)-doped alumino-silicate glass optical fiber was developed, and its temperature and vibration dependence on the Faraday Effect were investigated. Uniformly embedded Gd2O3 NPs were identified to form in the core of the fiber, and the measured absorption peaks of the fiber appearing at 377 nm, 443 nm, and 551 nm were attributed to the Gd2O3 NPs incorporated in the fiber core. The Faraday rotation angle (FRA) of the linearly polarized light was measured at 650 nm with the induced magnetic field by the solenoid. The Faraday rotation angle was found to increase linearly with the magnetic field, and it was about 18.16° ± 0.048° at 0.142 Tesla (T) at temperatures of 25 °C–120 °C, by which the estimated Verdet constant was 3.19 rad/(T∙m) ± 0.01 rad/(T∙m). The variation of the FRA with time at 0.142 T and 120 °C was negligibly small (−9.78 × 10−4 °/min). The variation of the FRA under the mechanical vibration with the acceleration below 10 g and the frequency above 50 Hz was within 0.5°.

Optical Absorption and EPR Studies on Gamma-Ray Irradiated RE 3+ -Doped Fluorophosphate Glasses

We have studied the effect of γ-ray irradiation on optical absorption, emission and decay characteristics of RE3+ (RE = Sm, Eu and Dy)-doped fluorophosphate glasses. Electron paramagnetic resonance (EPR) study confirms the POHC and PO3 EC defects induced in glasses by the γ-irradiation. The presence of induced defect centers significantly affects the optical and emission properties. The optical band gap values of the studied systems increased after the γ-ray irradiation. The phonon energy and electron–phonon coupling strength of Eu3+-doped fluorophosphate glass were determined from the phonon sideband analysis. The emission intensity of the RE3+ ions increased significantly after the γ-ray irradiation. The intensity parameter, R is the ratio of the intensities of the 5D0 → 7F2/5D0 → 7F1 transitions of Eu3+ ion and Y/B intensity parameter is the ratio of intensities of the 4F9/2 → 6H13∕2/4F9/2 → 6H15/2 transitions of Dy3+ ion reveal that the local environment around the RE3+ ion changed after the γ-ray irradiation in the present system. The lifetime of excited states of RE3+ ions decreased after the γ-ray irradiation due to the formation of defects induced by the γ-ray irradiation. The CIE color coordinates were determined before and after the γ-ray irradiation for the Dy3+-doped glass system.

Luminescence and decay characteristics of Tb3+-doped fluorophosphate glasses

ABSTRACT Tb3+-doped fluorophosphate glasses with the composition of P2O5–K2O–SrF2–Al2O3–x Tb4O7 (where x = 0.1, 0.5, 1.0, 2.0 and 4.0 mol%) were prepared by a conventional high temperature melt quenching technique and characterized through absorption, emission, excitation and decay measurements. From the emission studies, a strong green emission at around 546 was observed, which corresponds to the 5D4 → 7F5 transition of Tb3+ ion. Green/blue intensity ratios (IG/IB) were evaluated as a function of Tb3+ concentration and vice versa. Higher IG/IB intensity ratio confirms the higher covalency between Tb–O bond and higher asymmetry around the Tb3+ ions in the present fluorophosphate glasses. The decay curves for the 5D4 level of Tb3+ ion were measured and found that they exhibited single exponential nature irrespective to the dopant concentration. The experimental lifetime was determined using single exponential fitting and found that it increased from 2.65 to 2.95 ms when Tb3+ concentration increased from 0.1 mol% to 4.0 mol%. The derived properties were compared to the other Tb3+-doped glasses in order to see the potentiality of the material for visible laser gain media at 546 nm.

Spectroscopic Properties of Yb3+-Doped Silicate Glasses

Abstract Yb3+-doped silicate glasses (SiO2–Nb2O5–K2O–ZnF2) were prepared by a conventional melt quenching technique and their spectroscopic properties were investigated. The emission cross-section was found to be 0.53×10−20 cm2 at 1006 nm from the reciprocity method described by McCumber from the measured absorption spectrum of 1.0 mol% Yb2O3-doped glass. The lifetime (τexp) and figure of merit (σem×τexp) for the 2F5/2→2F7/2 transition of 1.0 mol% Yb2O3 -doped silicate glass, were evaluated to be 0.50 ms and 0.26 cm2 ms, respectively. The other spectroscopic parameters, βmin, Isat and Imin were found to be 0.17, 29.00 kW/cm2 and 4.90 kW/cm2, respectively. The results indicate that the present Yb3+-doped silicate glasses could be useful as laser gain media at 1006 nm.

Optical properties of Er 3+ -doped K-Ca-Al fluorophosphate glasses

Optical absorption and emission properties of the Er3+- doped K-Ca-Al fluorophosphate glasses were investigated and compared with other reported glasses for optical amplification application at 1.534 μm.