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1. 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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2. 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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3. Crystal growth and characterization of undoped and Dy-doped TlPb2Br5 for infrared lasers and nuclear radiation detection

   Hömmerich, U.; Brown, E.; Kabir, A.; Hart, D.; Trivedi, S.B.; Jin, F.; Chen, H. (September 2017, Journal of crystal growth)

   We report results of the crystal growth and characterization of undoped and Dy-doped TlPb2Br5 for applications in infrared (IR) lasers and nuclear radiation detection. TlPb2Br5 (TPB) was synthesized from commercial starting materials of PbBr2 and TlBr and further purified through a combination of zone-refinement and directional solidification. For doping experiments, 2 wt% of DyBr3 was added to the purified TPB material. Crystal growth of TPB and Dy: TPB was carried out in a two-zone tube furnace by a vertical Bridgman method. Following optical excitation at ~1.36um, the Dy: TPB crystal exhibited efficient mid-IR emission bands centered at 2.87um and 4.35um with room-temperature lifetimes of 9.5 ms and 5.2 ms, respectively. The peak emission cross-sections were determined to be ~0.8x10-20 cm2 and ~0.5x10-20 cm2, respectively, which makes Dy: TPB a promising candidate for mid-IR laser applications. Besides its potential as a solid-state laser host, an undoped TPB crystal was also tested for gamma-ray detection. Using Cs-137 and Am-241 sources resulted in energy resolutions for gamma-rays as good as 1-2% (FWHM) at room-temperature under non-optimized conditions. 

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4. Materials development and mid-infrared emission properties of Dy-doped TlPb2Br5 and CsPbCl3

   U. Hommerich, D. Hart (January 2020, Proc. SPIE 11276, Optical Components and Materials XVII)

   We report on the materials development and infrared (IR) optical spectroscopy of Dy3+-doped into the ternary lead halides compounds TlPb2Br5 and CsPbCl3 for photonic applications. The investigated Dy-doped ternary lead halides were synthesized from purified starting materials followed by melt-growth using vertical Bridgman technique. Under optical pumping at 1.35 m (6H15/26H9/2+6F11/2), broad mid-IR emissions in the ~2.9 µm (6H13/26H15/2), ~4.3 µm (6H11/26H13/2), and ~5.4 µm (6H9/2 +6F11/2 6H15/2) regions were observed at room-temperature. Compared to Dy: TlPb2Br5, the mid-IR emission from Dy: CsPbCl3 was significantly weaker suggesting the existence of non-radiative losses. Temperature dependent lifetime studies and a Judd-Ofelt analysis were performed for Dy: TlPb2Br5. 

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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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