Luminescence spectroscopy of Cr3+ ions in bulk single crystalline β-Ga2O3-In2O3 solid solutions.

Cr-doped monoclinic β-Ga 2 O 3 –7%In 2 O 3 single crystals were grown by the floating zone technique with radiation heating. The dark green color of the as-grown crystals transforms to light green upon crystals annealing in an oxygen atmosphere. Excitation spectra reveal characteristic Cr3+ bands in the visible spectral region and complex features in the UV region. Comparisons between as-grown and annealed crystals show variations in chromium excitation bands. UV or visible light irradiation induces intense Cr3+ luminescence in the red spectrum. The R 2 line diminishes at low temperatures, and the R 1 line dominates, exhibiting a blue shift compared to gallium oxide. Raman spectroscopy identifies phonon frequencies, revealing distinct modes associated with crystal lattice vibrations. The fine structure in the luminescence spectrum is attributed to vibronic transitions involving R lines and specific phonon modes. The R 1 line in β-Ga 2 O 3 –7%In 2 O 3 single crystals has a larger FWHM than in β-Ga 2 O 3. Decomposition of R 1 -line reveals inhomogeneous broadening, with Gaussian fits indicating several types of Cr3+ centers, attributed to the octahedrally-coordinated Ga- and In positions, as well as is sensitive to oxygen non-stoichiometry. Photoluminescence decay kinetics measured at 695 nm (R 1 (Ga)-line) have a single-exponential decay at lower temperatures with a lifetime of 2.8 ms at 4.5 K. Temperature dependence of lifetime for the studied crystals is consistent with the previously studied β-Ga 2 O 3 :Cr and confirms an application potential of the material for low-temperature non-contact luminescence thermometry and light sources in deep red or near-IR spectral region. • Cr-doped β-Ga 2 O 3 –7%In 2 O 3 crystals grown by the floating zone technique have been characterized. • The temperature dependences of the photoluminescence spectra of Cr3+ ions were studied. • R 2 line diminishes at low temps and R 1 line dominates, exhibiting blue shift compared to pure β-Ga 2 O 3. • Luminescence spectrum analysis reveals several types of Cr3+ centres. • Photoluminescence decay study at 695 nm suggests potential for low-temperature thermometry. [ABSTRACT FROM AUTHOR]