Althea Bluiett

Synthesis and spectroscopic properties of neodymium doped lead chloride

The crystal growth and infrared spectroscopic properties of Nd doped lead chloride (Nd:PbCl2) are reported. Lead halide based materials have recently emerged as laser hosts with low maximum phonon energies. In this work, Nd:PbCl2 crystals were grown by a self-seeded Bridgman technique. Following optical pumping at 750 and 808nm, Nd:PbCl2 exhibited several infrared (IR) emission lines between 800 and 1600nm as well as a broad mid-IR band centered at ∼5.19μm. It was found that for Nd3+ concentrations larger than ∼1×1019cm−3, the mid-IR emission is predominantly due to the transition I11∕24→I9∕24. From a Judd-Ofelt analysis, the radiative quantum efficiency of the 5.19μm emission was determined to be ∼27%. The multiphonon decay rates of several closely spaced Nd3+ transitions were modeled using the well known energy-gap law and the host dependent parameters B and β were determined to be 9.5×109s−1 and 1.26×10−2cm, respectively. The obtained energy-gap law parameters were subsequently used to describe the tem...

Spectroscopic characterization and upconversion processes under ~1.5 μm pumping in Er doped Yttria ceramics

We report on the spectroscopic characteristics and upconversion emission in Er3+ doped Yttria (Y2O3) transparent ceramics prepared by a modified two-step sintering method. The near-infrared (1.5 μm) emission properties were evaluated as a function of Er3+ concentration. Judd-Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were calculated and compared with results reported for Er3+ doped Y2O3 single crystal and nanocrystals. Following pumping at 1.532 μm, weak blue (~0.41 μm, 2H9/2→4I15/2), strong green (~0.56 μm, 2H11/2, 4S3/2→4I15/2) and red (~0.67 μm, 4F9/2→4I15/2) emission bands were observed as well as weak near-infrared emissions at 0.8 μm (4I9/2→4I15/2) and 0.85 μm (4S3/2→4I13/2) at room temperature. The upconversion emission properties under ~1.5 μm pumping were further investigated through pump power dependence and decay time studies. Sequential two-photon absorption leads to the 4I9/2 upconversion emission while energy transfer upconversion is responsible for the emission from the higher excited states 2H9/2, 2H11/2, 4S3/2, and 4F9/2. The enhanced red emission with increasing Er3+ concentration most likely occurred via the cross-relaxation process between (4F7/2 → 4F9/2) and (4I11/2 → 4F9/2) transitions, which increased the population of the 4F9/2 level.

Infrared absorption and fluorescence properties of Ho-doped KPb2Br5

Spectroscopic properties of the 2 μm infrared (IR) emission (5I7 → 5I8) from trivalent holmium (Ho3+) doped potassium lead bromide (KPb2Br5) are presented. The investigated Ho3+ doped KPb2Br5 (KPB) material was synthesized through purification of starting materials including multi-pass zone-refinement, bromination, and subsequently grown using horizontal Bridgman technique. The bromination process was critical for removing oxidic impurities and enhancing the quality of the crystal. Judd-Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were calculated and compared with results reported for Ho3+ doped KPb2Cl5 (KPC). Under resonant pumping (~1.907 μm), Ho: KPB showed a broad IR emission centered at ~2 μm with an exponential decay time of 7.1 ms at room temperature. The nearly temperature independent emission lifetime is consistent with a negligibly small non-radiative decay rate for the 5I7 excited state of Ho3+, as predicted by the multiphonon energy gap law. The optical absorption, emission and gain cross-sections of Ho: KPB were determined for the 2 μm transition. The Ho: KPB crystal was also evaluated as a potential solid-state material for laser cooling applications.

Mid-infrared luminescence properties of Cr/sup 2+/ and Co/sup 2+/ doped CdTe and cadmium manganese telluride

Summary form only given. In this paper we report new spectroscopic results of Cr/sup 2+/ doped Cd/sub 1-x/Mn/sub x/Te laser crystals, focusing on the mid-infrared absorption and luminescence properties. In addition, initial results of the mid-infrared luminescence from Cr:CdTe, Co:CdTe and Co:Cd/sub 1-x/Mn/sub x/Te are presented.

Optical spectroscopy of rare-earth doped ternary lead based halides

Spectroscopic properties of Pr3+ and Er3+ -doped KPb2Br5 crystals were investigated for possible applications in eye-safe lasers as well as Ce3+-doped KPb2Cl5 and Eu2+-doped KPb2Cl5/KPb2Br5 for potential radiation detectors. The studied materials were synthesized through careful purification of starting materials including multi-pass zone-refinement and halogenation. The growth of the purified materials was then carried out through the vertical or horizontal Bridgman technique. Under resonant excitation, infrared (IR) emissions at ~1.5 μm and ~1.6 μm were observed from Er:KPb2Br5 and Pr:KPb2Br5 corresponding to the 4f-4f transitions of 4I13/2→4I15/2 and 3F4,3F3→3H4, respectively. Emission characteristics of the ~1.5 μm Er3+ and ~1.6 μm Pr3+ transitions including IR to visible upconversion emission studies were also discussed. Under xenon lamp excitation, spectroscopic results showed allowed 5d-4f Ce3+ emission centered at ~375 nm in Ce3+-doped KPb2Cl5. Fast photoluminescence decay time of ~30-50 ns was attained from Ce:KPb2Cl5, while X-ray excited emission at ~530 nm appeared to originate from the host KPb2Cl5 crystal. In addition, a commercial Ce:YAP (yttrium aluminum perovskite, YAlO3) crystal was included in this study for comparison. Eu2+ 5d-4f emissions were not observed from Eu2+-doped KPb2Cl5 and KPb2Br5 crystals.

Optical properties of Pr3+-, Ce3+-, and Eu3+-doped ternary lead halides

The luminescent properties of rare-earth doped solids have been under intense exploration for a wide range of applications ranging from displays and lasers to scintillators. In this work, the material purification, crystal growth, and spectroscopic properties of Ce3+-, and Eu3+- doped KPb2Cl5 as well as Pr3+ doped KPb2Cl5 and KPb2Br5 were investigated for possible applications in infrared lasers and radiation detectors. The studied materials were synthesized through careful purification of starting materials including multi-pass zone-refinement and halogination. The growth of the purified materials was then carried out through vertical or horizontal Bridgman technique. The trivalent praseodymium ion (Pr3+) offers a large number of laser transitions in the visible and infrared (IR) spectral regions. Using ~1.45 μm and 1.9 μm pumping, IR emissions at ~1.6, ~2.4, and ~4.6 μm were observed from Pr: KPb2Cl5 and Pr: KPb2Br5 corresponding to the 4f-4f transitions of 3F4/3F3→3H4, 3F2/3H6→3H4, and 3H5→3H4, respectively. Large emission cross-sections in the range of (4.8-6.1) x 10-20 cm2 (near-IR, ~1.6 μm) and (5.5-6.0) x 10-20 cm2 (mid-IR, ~4.6 μm) were observed for both crystals. Emission characteristics of the ~1.6 μm Pr3+ transition including IR to visible upconversion emission studies were also discussed. Under Xenon lamp excitation, preliminary spectroscopic results showed allowed 5d-4f Ce3+ emission centered at ~375 nm in Ce3+ doped KPb2Cl5. In addition, commercial Ce:YAG and Ce:YAP crystals are included in this study for comparison. Pr3+ and Eu2+ 5d-4f emissions were not observed from Pr3+/Eu2+ doped KPb2Cl5 crystals.

Comparative spectroscopic studies of Ho: KPb2Cl5, Ho: KPb2Br2, and Ho: YAG for 2 μm laser cooling applications

The infrared (IR) absorption and emission properties of Ho:KPC, Ho:KPB, and Ho:YAG were compared for possible applications in 2 µm laser cooling. Ho:KPC and Ho:KPB crystals were grown by vertical Bridgman technique using purified starting materials. A commercial Ho:YAG crystal was included in this study for comparison. Under resonant pumping at ~1.907 µm, the Ho-doped KPC/KPB crystals exhibited broad IR emission centered at ~2 µm based on the Ho3+ intra-4f transition 5I7 → 5I8. Under similar experimental conditions, Ho:YAG showed a narrow-structured emission band reflective of individual Stark levels. The average emission wavelength for Ho:YAG was determined to be ~2.03 µm. Initial heat loading/cooling experiments under ambient air were performed using a fiber laser operating at ~2.036 µm with an output power of 2 W. The Ho:KPC/KPB crystals exhibited small temperature increases of ~1.0 ºC. A significantly larger temperature increase of ~5 ºC was observed for Ho:YAG. IR transmission studies revealed the existence of OH impurities in the Ho-doped halides, which possibly lead to non-radiative decay channels.

Upconversion and 1.5 µm - 1.6 µm infrared emission studies of Er3+ doped in the low phonon-energy hosts KPb2Cl5 and KPb2Br5 via 1.5 µm laser excitation

In this study, cw and pulsed 1532 laser excitation of the 4I13/2 band of Er3+ was explored in the low phonon-energy hosts KPb2Cl5and KPb2Br5. Crystal growth along with upconversion and eye-safe emission (~ 1550 nm) studies were conducted on both samplesunder 140 mW of cw laser excitation. Excitation spectra and emission decay transients of the infrared (4I9/2 →4I15/2) and green upconversion (2H11/2 + 4S3/2 →4I15/2) revealed that energy transfer upconversion (ETU) is the origin of the infrared and the green upconversion under 1532 nm excitation. Spectral emission measurements indicate that the infrared upconversion is dominant relative to the green upconversion in both Er: KPb2Cl5and Er: KPb2Br5 crystals.

Material Preparation and optical properties of Ho-doped KPb 2 Cl 5 and KPb 2 Br 5 for applications as mid-IR gain media

There continues to be great current interest in the development and characterization of solid state gain media for mid-IR lasers operating in the 3–5 µm region. Ho³⁺ doped crystals and glasses with low maximum phonon energies provide an attractive class of gain media for the ∼3.9 µm region [1–3]. For example, Tabirian et al. [3] reported pulsed mid-IR lasing at 3.9 µm using a Ho: BaY<inf>2</inf>F<inf>8</inf> (BYF) crystal. BYF has a maximum phonon energy of ∼ 415 cm⁻¹, which reduces non-radiative decay and improves the emission efficiency of the 3.9 µm laser transition (⁵I<inf>5</inf>➔⁵I<inf>6</inf>). In this work, comparative studies were performed on the material preparation and infrared spectroscopy of Ho³⁺- doped KPb<inf>2</inf>Cl<inf>5</inf> (KPC) and KPb<inf>2</inf>Br<inf>5</inf> (KPB) for applications as mid-IR gain media. KPC and KPB are non-hygroscopic crystals with narrow phonon spectra not exceeding ∼200 and ∼140 cm⁻¹, respectively. The maximum phonon energies of chloride and bromide crystals further reduce non-radiative relaxation compared to fluorides and enhance long wavelength IR emissions from trivalent rare-earth ions. The investigated Ho-doped KPC and KPB materials were synthesized through careful purification of commercial starting materials including directional freezing, zone-refinement, and halogination. The halogination process further removed oxidic impurities and enhanced the quality of the crystals. Under 890 nm laser excitation into the ⁵I<inf>5</inf> level, IR emissions centered at 1.2, 1.7, 2.0, 2.9, and 3.9 µm were observed in both crystals with transition assignments corresponding to ⁵I<inf>6</inf>➔⁵I<inf>8</inf>, ⁵I<inf>5</inf>➔⁵I<inf>7</inf>, ⁵I<inf>7</inf>➔⁵I<inf>8</inf>, ⁵I<inf>6</inf>➔⁵I<inf>7</inf>, and ⁵I<inf>5</inf>➔⁵I<inf>6</inf>, respectively (fig. 1). Further spectroscopic studies were conducted on the 3.9 µm emission arising from the ⁵I<inf>5</inf>➔⁵I<inf>6</inf> Ho³⁺ transition. The Ho-doped KPC and KPB crystals showed a peak emission cross section of ∼ 0.6 × 10⁻²⁰ cm⁻² at ∼3.96 µm, which is slightly lower than values reported for Ho-doped fluorides. However, the significantly longer ⁵I<inf>5</inf> emission lifetimes in the Ho-doped KPC and KPB crystals with values of ∼5.0 and 3.8 ms, respectively, resulted in higher σ-τ products compared to Ho-doped fluorides. The obtained spectroscopic results indicate that Ho: KPC and Ho: KPB are promising gain media for 3.9 µm laser applications.

Enhanced 5-µm emission in Tm,Tb: KPb[sub]2[/sub]Br[sub]5[/sub] and Tm,Nd:KPb[sub]2[/sub]Br[sub]5[/sub] for mid-infrared laser applications

We report on the 5 μm emission characteristics and energy transfer properties of Tb3+ doped KPb2Br5 and Nd3+ doped KPb2Br5 sensitized by Tm3+ ions. A series of co-doped samples of Tm,Tb: KPb2Br5 and Tm,Nd: KPb2Br5 samples were prepared from purified starting materials of PbBr2, KBr, and rare earth halides. Resonant excitation into the 3H6 → 3F4 absorption transition of Tm3+ at ~1760 nm resulted in an enhanced 5 μm emission from Tb3+ and Nd3+ ions in Tm,Tb: KPb2Br5 and Tm,Nd: KPb2Br5, respectively. The existence of energy transfer between Tm → Tb and Tm → Nd was further evidenced by the quenching of the emission decay times of the 3F4 → 3H6 transition of Tm3+ in doubly doped Tm,Tb: KPb2Br5 and Tm,Nd: KPb2Br5 compared to singly doped Tm: KPb2Br5.