Date of Graduation

1999

Document Type

Dissertation/Thesis

Abstract

This dissertation reports on the photoluminescence (PL) and optical absorption studies of two materials of interest for near-to-mid infrared (IR) laser sources: Cr2+:ZnSe and ZnGeP2. The first study uses optical absorption, PL and PL lifetime measurements to investigate the chromium impurity in ZnSe. Optical absorption at 296 K and at 5 K reveals three main features: the 5T2 → SE Cr2+ intracenter absorption peaked at 1.77 μm, the charge transfer band around 520 nm and a 680 nm absorption band, tentatively associated with the creation of Cr ion-pairs. Steady-state PL at 5 K under 514.5 nm excitation shows two near IR emissions: the 5E → 5T 2 emission peaked around 2.35 μm, and a 1 μm emission band. The decay of the 2.35 μm luminescence has been studied as a function of temperature and Cr concentration for two distinct excitation mechanisms. Under 1.9 μm Cr2+ intracenter excitation, this decay has a simple exponential form. Room-temperature (RT) lifetimes approximately ∼7 μs are measured for nCr2+ 1 x 1019 cm−3 is found. Two different behaviors of the decay time with temperature are found for samples with nCr2+ below and above this value, respectively. Under excitation into the charge transfer band (532 nm), on the other hand, the emission at wavelength longer than 2 μm is the superposition of two distinct components: a slow component and a fast component. A model is proposed to explain the 1 μm and 2.35 μm emissions under 532 nm excitation. The second study reports an unpolarized and polarized PL and optical absorption investigation of a series of sharp emission and absorption lines in nominally undoped ZnGeP2. Two sharp zero-phonon lines (ZPL) with perpendicular mutual polarization are resolved at 1.7849 eV (at T = 70 K) and 1.7784 eV (at T = 5 K) respectively, both in emission and in absorption. Thermalization occurs between these two ZPL in emission, suggesting a split excited state of the defect center involved. Considerable structural detail is resolved in the vibronic sideband of these ZPL, revealing two local-mode phonons with energies X1 = 6.3 ± 0.1 meV and X2 = 43.7 ± 0.1 meV in emission and X1′ = 7.3 ± 0.2 meV and X2′ = 43.1 ± 0.2 meV in absorption. These results are discussed and compared to somewhat similar spectra of isoelectronic impurities in GaP and ZnSiP2.

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