Time-Resolved and Steady-State Emission Properties of Dysprosium-Doped Lead Halide Based Crystals for Development of Mid-Infrared Gain Media

Graduate #89
Discipline: Physics
Subcategory: Materials Science

Daniel Hart - Hampton University
Co-Author(s): Eiei Brown and Uwe Hommerich, Hampton University, Hampton, VA Sudhir Trivedi, Brimrose Corporation of America, Sparks, MD

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The understanding of trace gases such as CO, CO2, CH4, and SO2 are necessary in the development of the chemistry and dynamics of Earth and other planets in our solar system. These and similar greenhouse molecules have strong absorption peaks in the mid-IR (3-10 µm). For laser remote sensing of trace gases, there is a need for the development of compact and efficient lasers operating in the mid-IR region. Among solid-state laser type materials, the oxide crystal YAG (Yttrium Aluminum Garnet) is the most widely used laser host and has high maximum phonon energy of ~ 700 cm-1. The large maximum phonon energy in YAG, however, leads to strong fluorescence quenching of rare earth centers for wavelengths > 2000 nm. Fluoride crystals such as BYF (Barium Yttrium Fluoride) have lower maximum phonon energies (<~ 415 cm-1) and have demonstrated efficient emission centered at ~3.4 µm from Dy3+ ions [1]. This study aims at providing a comparative analysis of the spectroscopic properties of Dy3+ doped into several lead halide based crystals including KPb2Cl5 (KPC), KPb2Br5 (KPB), and TlPb2Br5 (TPB). These halide crystals are considered non-hygroscopic and exhibit narrow phonon spectra of ~200 cm-1 for chlorides and ~140 cm-1 for bromides, respectively. The small maximum phonon energies are expected to greatly reduce fluorescence quenching at mid-IR emissions from rare earth ions. The investigated materials were synthesized from commercially available starting materials of PbCl2, PbBr2, KBr, and TlBr. Following several purification steps, bulk crystals were grown using vertical Bridgman technique resulting in small samples (~3mmx3mmx2mm) useful for initial spectroscopic studies. The transmission of these crystals were investigated using a FTIR spectrometer and revealed characteristic IR absorptions bands from Dy3+ transitions at ~1.1 µm (6H15/2 -> 6H7/2+6F9/2), ~1.3 µm (6H15/2 -> 6H9/2+6F11/2) , ~1.7 µm (6H15/2 -> 6H11/2), and ~2.9 µm (6H15/2 -> 6H13/2). Following cw diode laser pumping at ~1.75 µm, mid-IR emission bands centered at ~2.9 µm (6H13/2 -> 6H15/2) and ~4.4 µm (6H11/2 -> 6H13/2) were observed from all investigated crystals. Time-resolved emission studies using a pulsed Nd: YAG pumped optical parametric oscillator system operating revealed decay times of ~4-6 ms for the 4.4 µm band. Additional lifetime studies of different IR emission bands and transition cross-section calculations are still in progress and will be presented at the conference.

References: [1] Djeu, N. et al. (1997) Room-temperature 3.4-µm Dy:BaYb2F8laser. Optics Letters. Vol 22, Issue 13, Pg 997.

Funder Acknowledgement(s): NSF-CREST Center for Laser Science and Spectroscopy (CLaSS); NASA Pathways Research Engineering Fellowship

Faculty Advisor: Uwe Hommerich, uwe.hommerich@hamptonu.edu

Role: I performed the all the spectroscopy measurements and multiphonon relaxation calculations.