Date of Graduation
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 â†’ SE Cr2+ intracenter absorption peaked at 1.77 Î¼m, 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 â†’ 5T 2 emission peaked around 2.35 Î¼m, and a 1 Î¼m emission band. The decay of the 2.35 Î¼m luminescence has been studied as a function of temperature and Cr concentration for two distinct excitation mechanisms. Under 1.9 Î¼m Cr2+ intracenter excitation, this decay has a simple exponential form. Room-temperature (RT) lifetimes approximately âˆ¼7 Î¼s are measured for nCr2+ 1 x 1019 cmâˆ’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 Î¼m is the superposition of two distinct components: a slow component and a fast component. A model is proposed to explain the 1 Î¼m and 2.35 Î¼m 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 Â± 0.1 meV and X2 = 43.7 Â± 0.1 meV in emission and X1â€² = 7.3 Â± 0.2 meV and X2â€² = 43.1 Â± 0.2 meV in absorption. These results are discussed and compared to somewhat similar spectra of isoelectronic impurities in GaP and ZnSiP2.
Rablau, Corneliu Ioan, "Photoluminescence and optical absorption spectroscopy of infrared materials chromium(2+) doped zinc selenide and zinc germanium phosphide." (1999). Graduate Theses, Dissertations, and Problem Reports. 9613.