Absorption and luminescence spectroscopy of Cr4+-doped Ca2GeO4. A potential near infrared laser material

Sol−Gel Syntheses and Spectroscopic Characterization of Chromium-Doped Silicates and Germanates

“…Conversion to the crystalline orthorhombic phase changes the oxidation state and coordination of the chromium dopant. EPR spectra of Cr-doped Ca 2 SiO 4 and Ca 2 GeO 4 (Figure ) show a single resonance with g = 2.05 ± 0.02 and a half-width of 200 G. Although the half-width is significantly larger, the g value is within experimental error of that reported for aluminates, alkyls, , and oxide glasses , containing tetrahederally coordinated Cr 4+ and is attributed to tetrahedrally coordinated Cr 4+ . These resonances also resemble those observed in forsterite where Cr 4+ formation has been attributed to a reaction between Cr 3+ and excess oxygen defect centers. , In addition to the resonance attributed to tetrahederal Cr 4+ , all Cr-doped forsterite samples prepared in these experiments exhibit an additional resonance with g ≈ 5 and g ≈ 1.96 that are (Figure ) assigned to octahederally coordinated Cr 3+ . , …”

“…Forsterite and other olivine systems have been prepared by high-temperature processing techniques, − coprecipitation, and different sol−gel routes. − Systems that are isostructural with forsterite, Mg 2 SiO 4 , also exhibit near-IR emissions. ,, Forsterite, Mg 2 SiO 4 has an orthorhombic structure with the space group Pbnm and contains four formula units per unit cell. In the unit cell, Mg 2+ ions occupy two distinct octahedral coordination sites, M 1 with inversion symmetry ( C i ) and M 2 with mirror symmetry ( C s ), while Si 4+ occupies a tetrahedral coordination site .…”

“…[7][8][9][10][11][12][13] This site provides a low-symmetry field thought to be necessary for near-IR emission and laser action. [9][10][11][12][13] Forsterite and other olivine systems have been prepared by high-temperature processing techniques, [11][12][13][14][15] coprecipitation, 16 and different sol-gel routes. [17][18][19][20][21] Systems that are isostructural with forsterite, Mg 2 SiO 4 , also exhibit near-IR emissions.…”

Vibrational spectra of CaGa2O4, Ca2GeO4, CaIn2O4 and CaSnO3 prepared by electrospinning

“…These four excellent optical-function oxides with d 10 electron configuration are probably applied in water splitting and the photoluminescent field [9,10,[18][19][20]. Subsequently, structures and morphologies of these oxides were confirmed by X-ray powder diffraction, scanning electron microscopy, Raman spectroscopy and infrared spectroscopy, respectively.…”

Valence Stabilization, Mixed Crystal Chemistry, and Electronic Transitions in Tetrahedral Oxo and Hydroxo Cr(IV), Mn(V), and Fe(VI) Clusters: A Theoretic Investigation

“…Isoelectronic d cations Cr'4, Mn4, and Fe4' in various oxide ceramics have been subject to extensive studies, both experimental and theoretical, because of their remarkable luminescence properties (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) and applications, in the case of Cr'4, in tunable lasers in the near infrared (13)(14)(15)(16). The oxidation states of tetrahedrally coordinated Cr'4, Mn4, and Fe4' ions are rather unstable when compared to those of Cr''', Cr4', Mn'', Mn''', Mn'4, Mn4'', and Fe'''.…”