Preparation, structural and spectroscopic study of sol-gel-synthesized $$\hbox {Cr}^{3+}$$:$$\hbox {Al}_{2}\hbox {O}_{3}$$ powder

Abstract

Chromium-doped -Al 2 O 3 powder was synthesized by a modified sol-gel method using poly(vinyl alcohol) aqueous solutions and metal nitrate precursors. The synthesis process is simple, is of low cost and produced final crystals with cubic shape as confirmed by X-ray diffraction. The morphology of the samples verified by scanning electron microscopy showed slabs with thickness below 1 μm , formed by interconnected long grains of typical thickness of around 200 nm , showing growth of the grains as followed by thermogravimetric analysis. Luminescence characteristics of Cr 3+ were detected and analyzed as a function of the concentration of chromium using photoacoustic and photoluminescence spectroscopies.

Cr-doped Al2O3–YAG binary and Al2O3–YAG–ZrO2 ternary eutectic materials crystallized by the micro pulling down technique and their characterization

“…For this wavelength, the decay curves are particularly nonexponential due to the competition of the relaxation process from the excited level to the emitting 4 T 2 level and the partial thermal equilibrium with the 2 E levels. However, this thermal coupling being less efficient at a low temperature (77 K), it is observed that the values of decay times of the 4 T 2 → 4 A 2 allowed transition measured at 773.0 nm becomes shorter than at 300 K. Finally, the decay time of Cr-doped binary eutectics is in good agreement with Cr 3+ : Al 2 O 3 powder, 38 and ruby bulk crystals 40 especially considering the lifetime of about 1 ms for 2 at% of the Cr-Cr pair emission of the N-lines measured at 704 nm under 532 nm at low temperature. It is interesting to note that the lifetime of the emission of Cr pairs is much shorter in the ternary 0.3 ms than in the binary eutectics 0.8 ms.…”

“…Under the green excitation, Cr-doped Al 2 O 3 is clearly identified. 38 The sharp line centered at 694 nm corresponds to the forbidden spin transitions from 2 E to 4 A 2 level, referred to as R-line, and the broad band centered at 774 nm is due to the phonon-assisted 4 T 2 to ground state 4 A 2 . This last transition was mostly observed when Cr-doped Al 2 O 3 was higher than 0.5 at%.…”

“…Indeed, the relative intensity of the broad band centered at 774 nm is increasing with the concentrations. 38 This effect is magnified in Cr-doped ternary eutectics. Moreover, under the blue excitation, an additional sharp line around 688 nm appears, attributed to the 2 E → 4 A 2 transition of the Cr-doped YAG phase.…”