G. A. Kumar

Synthesis and spectroscopic characterization of CaF2:Er3+ single crystal for highly efficient 1.53 μm amplification

A CaF2:Er3+ single crystal was grown by the Tammann–Stober method. The potential of this material as a laser crystal for 1530 nm emission was established by quantitative analysis of the optical absorption and emission spectra. Assuming the tetragonal symmetry of the Er3+ sites, the Bkq crystal field parameters, Racah parameters, spin–orbit interaction parameters, and configuration interaction parameters were derived by fitting the experimental absorption band positions with the model energy Hamiltonian. Judd–Ofelt parametrization was done to compute the radiative decay time and fluorescence branching ratio of various meta stable transitions. Using the measured fluorescence decay time and computed radiative decay time, 100% quantum efficiency is obtained for the 1530 nm band, which is reasonable due to the low multiphonon relaxation, and absence of nonradiative energy transfer processes at the 0.01 at.% Er3+ concentration. The narrow bandwidth (13 nm) and high stimulated emission cross section (3.2×10−20 c...

Synthesis and optical properties of infrared-emitting YF3:Nd nanoparticles

Nd3+-doped YF3 (YF3:Nd) nanoparticles with a size of ∼20 nm were synthesized by solvothermal decomposition of yttrium and neodymium trifluoroacetate precursors in oleylamine. Using the 4f-energy matrix diagonalization procedure various interaction parameters: Slater–Condon (F2, F4, and F6), spin-orbit (ξ), two body interaction (α, β, and γ), Judd parameters (T2, T3, T4, T6, T7, and T8), spin-other-orbit parameters (M0, M2, and M4) and electrostatically correlated spin-orbit interaction parameters (P2, P4, and P6), and the crystal-field parameters (Bqk) were evaluated. The potential of YF3:Nd as a laser host for 1052 nm emission was evaluated by quantitative analysis of the absorption, emission spectra, and fluorescence decay characteristics. Judd–Ofelt parametrization was employed to compute the radiative spectral parameters such as radiative transition probabilities, fluorescence branching ratios, stimulated emission cross sections, and quantum efficiencies of the observed bands in the fluorescence spect...

Lanthanide Compounds with Fluorinated Aryloxide Ligands : Near-Infrared Emission from Nd, Tm, and Er

Ln(OC(6)F(5))(3) form stable, isolable compounds with 1,2-dimethoxyethane (DME). Monomeric (DME)(2)Ln(OC(6)F(5))(3) (Ln = Nd, Er, Tm) adopt seven coordinate structures with two chelating DME and three terminal phenoxide ligands. Both (py)(4)Er(OC(6)F(5))(3) and (THF)(3)Yb(OC(6)F(5))(3) were also prepared and structurally characterized, with the latter being a mer-octahedral compound with bond lengths that are geometry dependent. Emission experiments on crystalline powders of the Nd(III), Tm(III), and Er(III) DME derivatives show that these compounds are highly emissive near-infrared sources.

Optical properties of a transparent CaF2:Er3+ fluoropolymer nanocomposite

We report the observation of Er3+ fluorescence in an optically transparent CaF2:Er3+ perfluorocyclobutyl-based fluoropolymer composite. Under 980 nm excitation, fluorescence was observed at 1560 nm with a bandwidth of 93 nm. A quantitative analysis of the radiative properties yielded a radiative quantum efficiency of 29% corresponding to a measured lifetime of 4 ms and theoretical radiative decay time of 13.8 ms. Further, the estimated stimulated emission cross section was calculated to be 3×10−20cm2, and the maximum optical gain from the composite was estimated to be 1.78 dB∕cm with a pump threshold of 1.1 mW. This estimate demonstrates that it is possible to use polymer nanocomposites for active optical devices.

Solution synthesis and spectroscopic characterization of high Er3+ content LaF3 for broadband 1.5 μm amplification

Erbium-doped LaF3 transparent gels have been synthesized by the solution synthesis of metal inorganic precursors. The solid solubility of Er3+ can reach 60 mol %, which is almost double the solubility limit of Er3+ in LaF3 synthesized by the Bridgman technique. A quantitative analysis of the absorption and emission spectral data shows that the quantum efficiency of the 1.55 μm emission band is comparable to that of melt grown single crystal. However, the emission spectral width of the 1.55 μm band is found to be 40% greater than that of the melt grown single crystal, which extends the spectral bandwidth to 11 THz. The high solid solubility of Er3+ supports 36 cm−1 single pass optical gain, which is three times higher than that in zirconium barium lanthanum aluminum sodium glass. The high Er3+ concentration and spectral bandwidth enable LaF3:Er amplifiers to be made by a low-temperature solution-based technique.

NEAR INFRARED-EMITTING ER AND YB/ER DOPED CEF3 NANOPARTICULATES WITH NO VISIBLE UPCONVERSION

In this work, a host which interacts and enhanced energy transfer to the luminescent center such that it facilitates the infrared emission while avoiding undesired emissions was found. An intense emission at approximately 1530 nm with no other visible emissions was observed in Er- and Yb-Er- doped CeF3 nanoparticles upon excitation at approximately 975 nm. The average measured luminescence lifetimes of the approximately 1530 nm emission for heat-treated CeF3:Er and CeF3:Yb,Er nanoparticles was approximately 4.5-6.5 ms, with internal quantum efficiencies up to approximately 52-75%. These nanoparticles offer a vast range of potential applications, which include optical amplifiers, waveguides, laser materials and infrared imaging probes.

Optical spectroscopy and confocal fluorescence imaging of upconverting Er3+-doped CaF2 nanocrystals

Up-conversion emission and confocal fluorescence imaging of Er3+-doped CaF2 nanocrystals were investigated using infrared excitation. At Er3+ concentrations less than 2.8mol%, green emission was dominant while red prevailed at higher concentrations. The simultaneous green and red emission and change in relative intensities is explained with a mechanism utilizing concepts of TPA, ESA, ET, and CR processes.

Infrared fluorescence and optical gain characteristics of chalcogenide-bound erbium cluster-fluoropolymer nanocomposites

The infrared fluorescence and optical gain characteristics of optically transparent nanocomposites consisting of (THF)14Er10S6Se12I6 (“Er10”) or (DME)2Er(SC6F5)3 (“Er1”) clusters dissolved in a transparent hexafluoroisopropyl (6F) variant of a perfluorocyclobutyl (PFCB)-based fluoropolymer are reported. Under excitation at 980 nm, fluorescence was observed at 1540 nm from both Er10 and Er1 with a 3dB bandwidth of 96 and 60 nm, respectively. The maximum gain computed for Er10 and Er1 was 2.8 and 0.021dB∕cm, respectively. The corresponding threshold pump powers for Er10 and Er1 were calculated to be 1.7 and 0.2 mW, respectively. These computations are consistent with gain characteristics measured by the amplified spontaneous emission technique and suggest that these nanocomposites are promising materials for active optical devices.

Engineered solution synthesis of rare-earth nanomaterials and their optical properties

This paper will summarize our work on rare-earth nanomaterials for infrared photonic applications. Our research focuses the use of solvothermal methods to prepare these materials in particulate and molecular form with controlled physical and chemical characteristics. Thermochemical computations are used to facilitate direct crystallization of the desired material from the solvothermal medium. The impact of the chemical and physical characteristics of nanopowder and molecular characteristics on optical properties will be discussed in reference to conventional glasses and single crystals.