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1. Visible emission studies of melt-grown Dy-doped CsPbCl 3 and KPb 2 Cl 5 crystals

   https://doi.org/10.1364/OME.398498  

   Hommerich, Uwe ; Uba, Samuel ; Kabir, A. ; Trivedi, Sudhir B. ; Yang, Clayton ; Brown, Ei Ei ( July 2020 , Optical Materials Express)

   We report results of the optical properties of Dy-doped CsPbCl₃and KPb₂Cl₅bulk crystals for potential applications in yellow solid-state laser development. The crystals were synthesized from purified starting materials and melt-grown by vertical Bridgman technique. Optical transmission measurements revealed characteristic absorption bands from intra-4f transitions of Dy³⁺ions. Direct optical excitation at 455 nm (⁶H_15/2→⁴I_15/2) resulted in dominant yellow emission bands at ∼575 nm from the⁴F_9/2excited state of Dy³⁺ions. In addition, both crystals exhibited weaker emission lines in the blue (∼483 nm) and red (∼670 nm) regions. The peak emission-cross sections for the yellow transition (⁴F_9/2→⁶H_13/2) were determined to be ∼0.22 × 10⁻²⁰cm²for Dy: CsPbCl₃(λ_peak= 576.5 nm) and ∼0.59 × 10⁻²⁰cm²for Dy: KPb₂Cl₅(λ_peak= 574.5 nm). The spectral properties and decay dynamics of the⁴F_9/2excited state were evaluated within the Judd-Ofelt theory to predict total radiative decay rates, branching ratios, and emission quantum efficiencies.

    

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2. Mid-IR Emission Characteristics of Low-Phonon Erbium doped Ternary Chloride-based Single Crystals

   E. Brown, Z. D. ( April 2021 , Proc. SPIE 11682, Optical Components and Materials.)

   null (Ed.)

   The mid-infrared fluorescence properties of erbium (Er) doped low-phonon ternary chloride-based crystals (KPb2Cl5,Cs2HfCl6, CsPbCl3, CsCdCl3) have been investigated. All crystals were grown by vertical Bridgman technique. Following optical excitations at 805 nm and 660 nm, all Er3+ doped chlorides exhibited infrared emissions at ~2750, ~3500, and ~4500 nm at room temperature. The mid-infrared emission at 4500 nm originating from the 4I9/2 -> 4I11/2 transition showed long emission lifetime values of ~7.8 ms and ~11.6 ms for Er3+ doped Cs2HfCl6 and CsCdCl3 crystals, respectively. In comparison, Er3+ doped KPb2Cl5 and CsPbCl3 demonstrated shorter lifetimes of ~3 ms and ~1.8 ms, respectively. The temperature dependence of the 4I9/2 decay times was performed for Er3+ doped CsPbCl3 and CsCdCl3 crystals. We observed that the fluorescence lifetimes were nearly independent of the temperature, indicating a negligibly small non-radiative decay rate through multiphonon relaxation, as predicted by the energy gap law for low phonon energy hosts. The room temperature stimulated emission cross-sections for the 4I9/2 -> 4I11/2 transition were determined to be in a range of ~0.14-0.54 x 10-20 cm2 for the studied Er doped chloride crystals. 

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3. Spectroscopic Evaluation of Er: Ga2Ge5S13 Glass for Mid-IR Laser Applications

   E. Brown ; Z. D. Fleischman ; J. McKay ; U. Hommerich ; W. Palosz ; S. Trivedi ; and M. Dubinskii ( July 2022 , Optical materials express)

   We present mid-IR spectroscopic characterization of the low-phonon chalcogenide glass, Ga2Ge5S13 (GGS) doped with Er3+ ions. Under the excitation at ∼800 nm, Er3+:GGS exhibited broad mid-IR emission bands centered at ∼2.7, ∼3.5, and ∼4.5 µm at room temperature. The emission lifetime of the 4I9/2 level of Er3+ ions in GGS glass was found to be millisecond-long at room temperature. The measured fluorescence lifetimes were nearly independent of temperature, indicating negligibly small nonradiative decay rate for the 4I9/2 state, as can be expected for a low-maximum-phonon energy host. The transition line-strengths, radiative lifetimes, fluorescence branching ratios were calculated by using the Judd-Ofelt method. The peak stimulated emission cross-section of the 4I9/2 → 4I11/2 transition of Er3+ ion was determined to be ∼0.10×10−20 cm2 at room temperature. 

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4. Optical properties of undoped, Eu 3+ doped and Li + co-doped Y 2 Hf 2 O 7 nanoparticles and polymer nanocomposite films

   https://doi.org/10.1039/c9qi01181a  

   Gupta, Santosh K. ; Zuniga, Jose P. ; Abdou, Maya ; Ghosh, P. S. ; Mao, Yuanbing ( January 2020 , Inorganic Chemistry Frontiers)

   Desirable phosphors for lighting, scintillation and composite films must have good light absorption properties, high concentration quenching, high quantum efficiency, a narrow color emission, and so forth. In this work, we first show that undoped yttrium hafnate Y 2 Hf 2 O 7 (YHO) nanoparticles (NPs) display dual blue and red bands after excitation using 330 nm light. Based on density functional theory (DFT) calculations, these two emission bands are correlated with the defect states arising in the band-gap region of YHO owing to the presence of neutral and charged oxygen defects. Once doped with Eu 3+ ions (YHOE), the YHO NPs show a bright red emission, a long excited state lifetime and stable color coordinates upon near-UV and X-ray excitation. Concentration quenching is active when Eu 3+ doping reaches 10 mol% with a critical distance of ∼4.43 Å. This phenomenon indicates a high Eu 3+ solubility within the YHO host and the absence of Eu 3+ clusters. More importantly, the optical performance of the YHOE NPs has been further improved by lithium co-doping. The origin of the emission, structural stability, and role of Li + -co-doping are explored both experimentally and theoretically. DFT calculation results demonstrate that Li + -co-doping increases the covalent character of the Eu 3+ –O 2− bonding in the EuO 8 polyhedra. Furthermore, the YHOE NPs have been dispersed into polyvinyl alcohol (PVA) to make transparent nanocomposite films, which show strong red emission under excitation at 270 and 393 nm. Overall, we demonstrate that the YHO NPs with Eu 3+ and (Eu 3+ /Li + ) doping have a high emission intensity and quantum efficiency under UV and X-ray excitation, which makes them suitable for use as phosphors, scintillators and transparent films for lighting, imaging and detection applications. 

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5. Comparative steady-state and time-resolved emission spectroscopy of Mn doped CsPbCl3 perovskites nanoparticles and bulk single crystals for photonic applications

   U. Hommerich, J. Barnett ( April 2021 , SPIE Proceedings , Optical Components and Materials)

   null (Ed.)

   Manganese doped inorganic halide perovskites continue to be of current interest for applications in light emitting devices and down-converters in solar cells. In this work we prepared Mn doped CsPbCl3 (Mn: CPC) bulk crystals and nanoparticles (NPs) and compared their emission properties. Bulk crystals were grown from the melt by vertical Bridgman technique and NPs were synthesized using a microwave assisted method. Under ultraviolet excitation at 350 nm, bulk crystal and NPs exhibited a broad orange emission centered in the ~600 nm range at room temperature. The broadbandemission was assigned to the intra-3d transition 4T1 → 6A1 of Mn2+ ions incorporated in the CPC host lattice. The Mn2+emission lifetimes were nearly exponential with values of 1.1 ms for NPs and 0.7 ms for the bulk crystal. NPs also showed exciton emission peaking at ~402 nm, whereas the bulk crystal exhibited no emission near the band-edge. Instead, the bulk material revealed a weak below-gap emission in the 450-550 nm region suggesting the existence of defect states. The excitation spectra for the orange Mn2+ emission from NPs and bulk crystals of Mn: CPC were significantly different indicating distinct excitation pathways. The excitation spectrum of the orange Mn2+ emission from NPs showed excitonic structure similar to the absorption spectrum suggesting an efficient energy transfer from excitons to Mn2+ ions. In contrast, UV excitation was less efficient for the bulk crystal and the excitation was dominated by below-gap excitation bands centered at 427 and 500 nm. 

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