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The maximum optical-absorption cross section of Cr2+ ions was evaluated from near-infrared (NIR) absorption spectroscopy and direct measurements of the chromium concentration in Cr2+:CdSe crystals. The emission lifetime of the excited state, 5E, of Cr2+ was measured as a function of Cr2+ concentration in the 2 × 1017-2 × 1018 ions/cm3 range and as a function of temperature from 77-300 K. Lifetime values were as high as ∼6 µs in the 77-250 K range and decreased to ∼4 µs at 300 K because of nonradiative decays. Assuming that most of the Cr dopant is in the Cr2+ state, an optical-absorption cross section σa of (1.94 ± 0.56) × 10-18 cm2 was calculated. Implications for laser performance are discussed.

Transition metals in the group II-VI semiconductors have attracted considerable attention for their application as tunable mid-infrared (IR) lasers at room temperature. Very recently, Co-doped II-VI hosts have been considered as saturable absorber materials. In the present study, we have grown both Cr-doped and Co-doped CdSe by a high-temperature solution growth technique using Se as solvent. The Cr-doped CdSe was grown in 4,000-ppm concentration. The Co-doped CdSe crystals were grown in concentrations of 2,000 ppm and 4,000 ppm. The crystals were characterized by optical-absorption spectroscopy. The absorption-peak position for Cr was 1.92 µm, and for Co, the peak position was 1.8 µm. The doping concentrations for Cr-doped samples were estimated from optical-absorption spectra using the Beer-Lambert law. Good-quality, crack-free single crystals were grown; however, our near-IR transmission microscopy showed Se inclusions, which were also confirmed by differential scanning calorimetry (DSC). The electrical-resistivity dependence on doping concentrations is presented and discussed. Glow discharge mass spectrometric (GDMS) measurements for the Co-doped sample are reported. The absorption cross section for Co was calculated for the first time using the Beer-Lambert law.

The spectral resolution of cadmium zinc telluride (CZT) room temperature nuclear radiation detectors is often limited by the presence of conducting surface species that increase the surface leakage current. Surface passivation plays an important role in reducing this surface leakage current and thereby decreasing the noise of the detectors and improving the spectral energy resolution. Chemical etching with a Br-MeOH solution leaves CZT surfaces rich in Te and is considered as one of the primary causes of the increased surface leakage current. Previous studies have shown that hydrogen peroxide (H2O2) forms oxides of tellurium on the CZT surface and thus acts as a good passivating agent. In this study we will present results on the use of potassium hydroxide (KOH) as an alternative passivating agent. The KOH aqueous solution leaves a more stoichiometric (evaluated from the trends in the surface Cd:Te ratio) and smoother CZT surface. The passivation effects of KOH solution on the surface of the CZT have been characterized by current-voltage measurements for different KOH concentrations and etching times for both parallel strip electrodes as well as a metal-semiconductor-metal configuration. The surface chemical composition and its morphology were studied by scanning x-ray photoelectron spectroscopy and atomic force microscopy. The comparison and demonstration of improvements in the spectral resolution of the CZT detectors (based on 241Am spectra) with and without the KOH treatment are presented.

A large photorefractive effect was measured in CdS0.8Se0.2:V and Cd0.55Mn0.45Te:V ternary crystals which shows promise for many device applications such as optical signal processing and optical limiting. In this study, we compared the results obtained from two-wave mixing experiments with Cd0.55Mn0.45Te:V and CdS0.8Se0.2:V crystals at the 633 nm wavelength. As the signal to pump beam ratio was varied from 10−1 to 10−4, Cd0.55MN0.45Te:V and CdS0.8Se0.2:V showed a maximum photorefractive gain of 0.17 and 0.20 cm−1, respectively. The grating formation time of both the crystals were measured to be in the milli-second range at an incident intensity of 200 mW/cm2.

ZnSe:Cr2+ is an attractive candidate as a room-temperature tunable solid-state laser with output in the 2–3 µm range. Passive absorption losses in this emission range currently limit laser performance. In this study, we use absorption and photoluminescence spectroscopies at 5 and 296K to address the origin of these optical losses. A series of diffusion-doped ZnSe:Cr single-crystal samples with Cr2+ concentrations in the range from 2×1017 cm−3 to 9×1019 cm−3 were obtained using CrSe powder as the dopant source. We find that trace amounts of Fe2+ produce absorption in the 2–3 µm range. Also, we have obtained data on a 680 nm absorption band observed in ZnSe:Cr which has been assigned to an internal transition of Cr2+. In our series of samples, the relative intensities of the 680 nm absorption band do not track the relative intensities of the 1.8 µm band (known to be due to Cr2+), although excitation near 680 nm does produce weak Cr2+ luminescence. Our absorption data do not support the current assignment of the 680 nm absorption as being an internal transition of the Cr2+ ion.