Purification, material synthesis, and infrared emission from Nd doped PbBr 2 and PbI 2
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0891-EE03-12.1
Purification, material synthesis, and infrared emission from Nd doped PbBr2 and PbI2 U. Hömmerich*,+, Ei Ei Nyein*, S.B. Trivedi**, A.G. Bluiett***, and J. M. Zavada**** * Hampton University, Department of Physics, Hampton, VA 23668 ** Brimrose Corporation of America, 19 Loveton Circle, Baltimore, MD 21152 *** Elizabeth City State University, Dept. of Chemistry and Physics, Elizabeth City, NC 27909 **** US Army Research Office, Durham, NC 27709 +
e-mail: [email protected]
ABSTRACT We report on the material synthesis and infrared optical properties of Nd doped lead bromide (PbBr2) and lead iodide (PbI2) bulk crystals. Commercial PbBr2 and PbI2 materials were purified through repeated solidification and horizontal zone refinement. After purification, Nd doped lead halides were synthesized and grown by Bridgman technique. Under optical excitation, Nd: PbBr2 samples exhibited several near-infrared emission bands centered at 816 nm, 891 nm, 963 nm, 1069 nm, 1183 nm, 1356 nm, and 1535 nm. The emission from Nd: PbI2 samples was similar to that from Nd: PbBr2, but slightly shifted to longer wavelengths. The observation of 1540 nm emission from Nd3+ ions is unusual and reflects on the small nonradiative decay rates in the investigated halides. Lead halides have low maximum phonon energies, which reduces non-radiative decay due to multi-phonon relaxations. In contrast to Nd: YAG, Nd: PbBr2 and Nd: PbI2 exhibited efficient emission from the 4F5/2, 2H9/2 excited states, which are located only ~1000 cm-1 above the 4F3/2 level of Nd3+. Under 808 nm diode pumping, both samples also exhibited broad mid-infrared emission bands centered at ~5.1 µm. INTRODUCTION Lead halides (PbBr2, PbI2) are promising materials for room-temperature nuclear radiation detectors [1-3]. PbBr2 and PbI2 are considered wide-gap semiconductors with bandgap energies of ~ 2.5 eV and ~2.3 eV, respectively [1-3]. The high atomic number of the cation and the large bandgap energies make these materials attractive candidates for scintillators or semiconductor detectors [1-3]. Recently, PbBr2 based ternary lead halides (e.g. KPb2Br5 and RPb2Br5) were investigated by several research groups as host materials for infrared solid-state lasers [4-7]. The low maximum phonon energy of binary and ternary based lead halides provides an effective means for achieving efficient emission from rare earth ions at long wavelengths [4-7]. Some initial results on the emission [8] and laser properties [9] of Nd doped PbCl2 were also recently reported. In this work, we have performed studies on the purification and synthesis of Nd doped PbBr2 and PbI2 bulk crystals and evaluated their emission properties for infrared light source development. EXPERIMENTAL DETAILS Commercial starting materials of high purity and ultra-dry PbBr2 and PbI2 were loaded separately into pre-cleaned quartz ampoules inside an argon-purged glove box. The materials were further dried under vacuum at a temperature of ~ 120 ºC for 24 hours before vacuum
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sealing. The melt
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