Dhiraj K. Sardar

Judd–Ofelt analysis of the Er3+(4f11) absorption intensities in phosphate glass: Er3+, Yb3+

A spectroscopic Judd–Ofelt investigation has been performed on Er3+ in the doubly doped phosphate glass:Er3+, Yb3+ in order to assess its potential as a laser system. The standard Judd–Ofelt model was applied to the room-temperature absorption intensities of Er3+(4f11) transitions to determine the intensity parameters: Ω2=6.28×10−20 cm2, Ω4=1.03×10−20 cm2, and Ω6=1.39×10−20 cm2 in the phosphate glass host. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) and branching ratios of the Er3+ transitions from the excited-state J manifolds to the lower-lying J′ manifolds. The radiative lifetimes of these excited states are determined from the radiative decay rates. The predicted decay rates and radiative lifetimes are compared to those of Er3+ transitions in other glass hosts. The quantum efficiency of the eye-safe laser transition 4I13/2→4I15/2 (1.54 μm) of Er3+ is approximately 80% in the phosphate glass host.

Optical characterization of melanin.

The optical properties of melanin have been characterized for a number of laser wavelengths in the visible region. The index of refraction of melanin is measured by the conventional method of minimum deviation using a hollow quartz prism at these wavelengths. The inverse adding doubling method based on the diffusion approximation and radiative transport theory have been employed to determine the absorption, scattering, and scattering anisotropy coefficients of melanin from the measurements of diffuse transmission, diffuse reflection and collimated transmission using double integrating spheres. The results obtained by the use of inverse adding doubling method have been compared to the Monte Carlo simulation technique.

Optical properties of whole blood

Abstract. The optical properties of whole blood are presented for the argon ion laser (488 nm) and He-Ne laser (633 nm) wavelengths. Applying the inverse adding-doubling (IAD) method, the absorption and scattering coefficients and scattering anisotropy coefficient of blood have been determined from the measurements of total diffusive reflectance and transmittance obtained by an integrating sphere at 488 nm. The scattering anisotropy coefficient obtained from the IAD method has been compared with that obtained independently by the goniometric measurements. The index of refraction of blood has been measured by the conventional minimum deviation method using an equilateral hollow quartz prism at 633 nm.

Judd-ofelt analysis of the Er3+ (4f11) absorption intensities in Er3+-doped garnets

Spectroscopic and laser properties of three different Er3+−doped garnet systems are characterized by employing the Judd–Ofelt (JO) analysis. The three garnet hosts are Y3Al5O12 (YAG), Y3Sc2Ga3O12 (YSGG), and Gd3Ga5O12 (GGG). The JO model has been applied to the room temperature absorption intensities of Er3+ (4f11) transitions to establish the so-called JO intensity parameters: Ω2, Ω4, and Ω6 in the three garnet hosts. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) and branching ratios of the Er3+ transitions from the excited state J manifolds to the lower-lying J′ manifolds. The predicted decay rates and branching ratios of these Er3+ transitions in YAG, YSGG, and GGG hosts are compared. From the radiative decay rates, the radiative lifetimes of the Er3+ excited states are determined in the three garnets and are also compared. We also report the spectroscopic quality factors, Ω4/Ω6, obtained for the three garnets. The quantum efficiencies ...

A new contribution to spin‐forbidden rare earth optical transition intensities: Gd3+ and Eu3+

Quantitative calculations show that numerous spin‐forbidden linear optical transitions observed in trivalent rare earth ions acquire a major fraction of their intensity from hitherto neglected contributions involving spin–orbit linkages within excited configurations. Motivated by the importance of analogous linkages previously demonstrated in two‐photon absorption, we derive a general expression applicable for all lN→lN transitions which can be incorporated into a revised Judd–Ofelt analysis of observed intensities. Presenting this revised analysis of observed linear absorption intensities for Gd3+ and Eu3+, we show that the new contribution is often comparable to standard contributions. With substantial modification of previously fitted phenomenological parameters, an improved fit to observed intensities is achieved, suggesting that reanalysis of linear intensity data for all trivalent rare earths is warranted.

Absorption intensities and emission cross sections of Tb3+ (4f8) in TbAlO3

Trivalent terbium absorption intensities in single-crystal TbAlO3 are analyzed using the Judd-Ofelt model to assess the crystal’s potential as a solid state laser system. The standard Judd-Ofelt model was applied to the room temperature absorption intensities of Tb3+ (4f8) to determine the phenomenological intensity parameters Ω2, Ω4, and Ω6. Seven multiplet manifolds are identified and the absorption intensities of these manifolds are least-squares fitted to the calculated intensities to obtain the intensity parameters: Ω2=40.52×10−20cm2, Ω4=8.74×10−20cm2, and Ω6=2.26×10−20cm2 in TbAlO3. These intensity parameters are then applied to determine the radiative decay rates and branching ratios of Tb3+ transitions from the D45 to the FJ′7 multiplet manifolds. Based on the results, the radiative lifetime of the excited state manifold D45 is determined from the radiative decay rates and found to be 3.5ms. The calculated lifetime is longer than the measured lifetime, reflecting the nonradiative interactions betw...

Optical absorption and emission from irradiated RbMgF3:Eu2+ and KMgF3:Eu2+

Abstract The optical properties of irradiated RbMgF 3 :Eu 2+ and KMgF 3 :Eu 2+ have been investigated. Previous research has shown that Eu 2+ ions in unirradiated RbMgF 3 give rise to broad band absorption around 250 nm and sharp intense line emission at 360 nm. When this material is irradiated little or no change occurs in the 250 nm absorption, but the lifetime of the Eu 2+ 360 nm transition is reduced. In addition, new emission is observed at 680 nm. In the case of irradiated KMgF 3 :Eu 2+ two new emission bands are observed at 600 and 800 nm. All of these transitions have short lifetimes and are not due to Eu 3+ ions.

Absorption intensities and emission cross sections of principal intermanifold and inter-stark transitions of Er3+(4f11) in polycrystalline ceramic garnet Y3Al5O12

A comparative spectroscopic study is performed on Er3+(4f11) ions doped in polycrystalline ceramic garnet Y3Al5O12 (YAG) and single-crystal laser rod, both containing nominal 50 at. % of Er3+. The standard Judd–Ofelt (JO) model is applied to the room-temperature absorption intensities of Er3+(4f11) transitions in both hosts to obtain the phenomenological intensity parameters. These parameters are subsequently used to determine the radiative decay rates, radiative lifetimes, and branching ratios of the Er3+ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds LJ2S+1 of Er3+(4f11) in these garnet hosts. The emission cross sections of the intermanifold Er3+I13∕24→I15∕24 (1.5 μm) transition as well as the principal inter-Stark transition Y1→Z4 (1550 nm) within the corresponding multiplet manifolds have been determined. The room-temperature fluorescence lifetimes of the I13∕24→I15∕24 (1.5 μm) transition in both polycrystalline ceramic and single-crystal YAG sample...

Stokes emission in GdF3:Nd3+ nanoparticles for bioimaging probes

There is increasing interest in rare earth (RE) doped nanoparticles (NPs) due to their sharp absorption and photoluminescence (PL) in the near infrared (NIR) spectral region. These NIR based nanoparticles (NPs) could allow biological imaging at substantial depths with enhanced contrast and high spatial resolution due to the absence of auto fluorescence in biological samples under infrared excitation. Here, we present the highly efficient infrared photoluminescence in GdF₃:Nd(3+) nanoparticles under 800 nm excitation within the hydrodynamic size limitations for bio-applications. The downconversion (Stokes emission) absolute quantum yields (QY) in powder, polymaleic anhydride-alt-1-octadicene (PMAO) coated powder and colloidal solutions have been investigated. QY measurements have revealed that downconversion (Stokes emission) QYs of approximately 5 ± 2 nm sized GdF₃:1% Nd(3+) colloidal NPs are 2000 times higher than those of efficient upconversion (UC) particles NaYF₄:20% Er/2% Yb of the same size. Furthermore, the utility of these NIR emitting nanoparticles for bioimaging probes has been demonstrated by confocal imaging and spectroscopic study.

Spectroscopic analysis of the Er3+(4f11) absorption intensities in NaBi(WO4)2

A spectroscopic analysis is performed on Er3+ (4f11) ions doped in NaBi(WO4)2 (NBWO) in order to assess this material for its potential as a near-infrared laser. The Judd–Ofelt model is applied to the room-temperature absorption intensities of Er3+ (4f11) in NBWO to obtain the three phenomenological intensity parameters: Ω2=5.50×10−20 cm2, Ω4=1.00×10−20 cm2, and Ω6=0.71×10−20 cm2. The intensity parameters are then used to determine the radiative decay rates (emission probabilities), radiative lifetimes, and branching ratios for the Er3+ transitions from the excited state multiplet manifolds to the lower lying manifold states. Using the radiative decay rates for the Er3+ (4f11) transitions between the corresponding excited states and the lower lying states, the radiative lifetimes of eight excited states of Er3+ are determined in this host. Using the measured room temperature fluorescence lifetime of approximately 4.75 ms and the radiative lifetime of 5.63 ms as predicted by the Judd–Ofelt model for the 4I13/2→4I15/2 (1.52 μm) transition of Er3+ in NBWO the quantum efficiency is determined to be approximately 84% for this laser material.A spectroscopic analysis is performed on Er3+ (4f11) ions doped in NaBi(WO4)2 (NBWO) in order to assess this material for its potential as a near-infrared laser. The Judd–Ofelt model is applied to the room-temperature absorption intensities of Er3+ (4f11) in NBWO to obtain the three phenomenological intensity parameters: Ω2=5.50×10−20 cm2, Ω4=1.00×10−20 cm2, and Ω6=0.71×10−20 cm2. The intensity parameters are then used to determine the radiative decay rates (emission probabilities), radiative lifetimes, and branching ratios for the Er3+ transitions from the excited state multiplet manifolds to the lower lying manifold states. Using the radiative decay rates for the Er3+ (4f11) transitions between the corresponding excited states and the lower lying states, the radiative lifetimes of eight excited states of Er3+ are determined in this host. Using the measured room temperature fluorescence lifetime of approximately 4.75 ms and the radiative lifetime of 5.63 ms as predicted by the Judd–Ofelt model for the 4I...