High spectral resolution, real-time, Raman spectroscopy in shock compression experiments Rev. Sci. Instrum. 82, 083109 (2011) Abnormal temperature dependent photoluminescence of excited states of InAs/GaAs quantum dots: Carrier exchange between excited states and ground states J. Appl. Phys. 109, 113540 (2011) Two-dimensional infrared spectroscopy of isotope-diluted ice Ih J. Chem. Phys. 134, 204505 (2011) Efficient nonradiative energy transfer from InGaN/GaN nanopillars to CdSe/ZnS core/shell nanocrystals Appl. Phys. Lett. 98, 163108 (2011) Time-resolved photoelectron spectroscopy of low-energy excitations of 4×4 C60/Cu(111) J. Chem. Phys. 133, 234704 (2010) Additional information on J. Appl. Phys.

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The primary excited state decay processes relating to the H613/2→H615/2∼3 μm laser transition in singly Dy3+-doped fluoride (ZBLAN) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the F69/2, H67/2 energy levels at 1125 nm and F611/2, H69/2 energy levels at 1358 nm established that the energy levels above the H611/2 level, excluding the F49/2 level, are entirely quenched by multiphonon emission in ZBLAN glass. The H611/2 and H613/2 energy levels emit luminescence with peaks at ∼1700 and ∼2880 nm, respectively, but at low quantum (luminescence) efficiencies. The quantum efficiency of the H611/2 level and H613/2 level is ∼9×10−5 and ∼1.3×10−2, respectively, for [Dy3+]=0.5 mol % based on calculations of the radiative lifetimes using the Judd–Ofelt theory. Excited state absorption (ESA) was detected by monitoring the rise time of the 1700 nm luminescence after tuning the probe wavelength across the spectral range from 1100 to 1400 nm. As a result of nonradiative decay of the higher excited states, ESA contributes to the heating of ∼3 μm fiber lasers based on Dy3+-doped fluoride glass. For [Dy3+] up to 4 mol %, we found no evidence of energy transfer processes between Dy3+ ions that influence the decay characteristics of the H611/2 and H613/2 energy levels.

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The deactivation of the two lowest excited states of Ho 3+ was investigated in Ho 3+ singly doped and Ho 3+ , Pr 3+-codoped fluoride ͑ZBLAN͒ glasses. We establish that 0.1-0.3 mol % Pr 3+ can efficiently deactivate the first excited ͑ 5 I 7 ͒ state of Ho 3+ while causing a small reduction of ϳ40% of the initial population of the second excited ͑ 5 I 6 ͒ state. The net effect introduced by the Pr 3+ ion deactivation of the Ho 3+ ion is the fast recovery of the ground state of Ho 3+. The Burshstein model parameters relevant to the Ho 3+ → Pr 3+ energy transfer processes were determined using a least squares fit to the measured luminescence decay. The energy transfer upconversion and cross relaxation parameters for 1948, 1151, and 532 nm excitations of singly Ho 3+-doped ZBLAN were determined. Using the energy transfer rate parameters we determine from the measured luminescence, a rate equation model for 650 nm excitation of Ho 3+-doped and Ho 3+ , Pr 3+-doped ZBLAN glasses was developed. The rate equations were solved numerically and the population inversion between the 5 I 6 and the 5 I 7 excited states of Ho 3+ was calculated to examine the beneficial effects on the gain associated with Pr 3+ codoping.

Ultraviolet (UV) fluorescence of Nd3+ ions induced by multistep laser excitation was investigated in Nd-doped LiYF4 and LiLuF4 crystals using a technique of time-resolved spectroscopy. The observed UV luminescence was due to transitions between the bottom of 4f25d configuration and the 4f3 states of Nd3+ ions. The first absorption band of 4f25d configuration, which starts around 56 700 cm−1, was excited by three stepwise absorptions of photons in the green (500–535 nm) from a short pulse laser excitation leading to broad emission bands in UV range (180–280 nm). An excitation band in the blue (468–486 nm) was observed due to the excitation of the second absorption band of 4f25d configuration around 63 000 cm−1 according to the photon absorption sequence: I9/24+hν(480 nm)→2G(1)9/2+hν(480 nm)→2F(2)7/2+hν(480 nm)→4f25d(second). The observed UV emissions (180–280 nm) from the bottom of the 4f25d configuration (first state) have a lifetime of 35 ns (parity allowed) and are broadband in contrast to UV emissions from 4f3 configuration, which are also present in the luminescence investigation but having a longer lifetime (8.5 μs) and structures composed of narrow lines. The excitation spectrum of fast UV luminescence exhibited different structures depending on the excitation geometry (σ or π) with respect to the c axis of the crystal. We observed two emissions from the first state of 4f25d configuration with peaks at 535 and 595 nm modifying the luminescence branching ratio of the bottom of the 4f25d configuration around 55 500 cm−1. The equivalent cross section of three and two excitation processes was estimated at 510 nm by solving the rate equations of the system under short laser excitation, which shows that is possible to have laser action under pulsed laser pumping with intensity below the crystal damage threshold.

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The primary excited state absorption processes relating to the 5 I 6 → 5 I 7 3 m laser transition in singly Ho 3+ -doped fluoride glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 5 I 6 and 5 I 7 energy levels established the occurrence of two excited state absorption transitions from these energy levels that compete with previously described energy transfer upconversion processes.