Anti-Stokes luminescence in chromium-doped ZnSe

Mid-IR photoluminescence of Fe(2+) and Cr(2+) ions in ZnSe crystal under excitation in charge transfer bands

Spectroscopic characterization of Fe:ZnSe(Cr:ZnSe) crystals under visible excitation into the charge transfer bands of Transition Metal ions were studied. The excitation efficiencies of mid-IR photoluminescence between (5)T(2)((5)E) and (5)E((5)T(2)) states via direct relaxation to the upper laser levels and via metastable upper (3)T(1) were investigated. It was demonstrated that the latter route is the dominant process for Cr(2+) ions and could provide sufficient pump rate for mid-IR lasing. The pump efficiencies via direct relaxation to the upper laser levels were estimated to be <2% for both ions under 532 nm excitation wavelength.

Photoluminescence of Anatase and Rutile TiO2Particles†

Nonaqueous reactions between titanium(IV) chloride and alcohols (benzyl alcohol or n-butanol) were used for the synthesis of anatase TiO2 particles, while rutile TiO2 particles were synthesized in aqueous media by acidic hydrolysis of titanium(IV) chloride. The X-ray diffraction measurements proved the exclusive presence of either the anatase or the rutile phase in prepared samples. The photoluminescence of both kinds of particles (anatase and rutile) with several well-resolved peaks extending in the visible spectral region was observed, and the quantum yield at room temperature was found to be 0.25%. Photon energy up-conversion from colloidal anatase and rutile TiO2 particles was observed at low excitation intensities. The energy of up-converted photoluminescence spans the range of emission of normal photoluminescence. The explanation of photon energy up-conversion involves mid-gap energy levels originating from oxygen vacancies.