Manganese Luminescent Centers of Different Valence in Yttrium Aluminum Borate Crystals

We present an extensive study of the luminescence characteristics of Mn impurity ions in a YAl3(BO3)4:Mn crystal, in combination with X-ray fluorescence analysis and determination of the valence state of Mn by XANES (X-ray absorption near-edge structure) spectroscopy. The valences of manganese Mn2+(d5) and Mn3+(d4) were determined by the XANES and high-resolution optical spectroscopy methods shown to be complementary. We observe the R1 and R2 luminescence and absorption lines characteristic of the 2E ↔ 4A2 transitions in d3 ions (such as Mn4+ and Cr3+) and show that they arise due to uncontrolled admixture of Cr3+ ions. A broad luminescent band in the green part of the spectrum is attributed to transitions in Mn2+. Narrow zero-phonon infrared luminescence lines near 1060 nm (9400 cm−1) and 760 nm (13,160 cm−1) are associated with spin-forbidden transitions in Mn3+: 1T2 → 3T1 (between excited triplets) and 1T2 → 5E (to the ground state). Spin-allowed 5T2 → 5E Mn3+ transitions show up as a broad band in the orange region of the spectrum. Using the data of optical spectroscopy and Tanabe−Sugano diagrams we estimated the crystal-field parameter Dq and Racah parameter B for Mn3+ in YAB:Mn as Dq = 1785 cm−1 and B = 800 cm−1. Our work can serve as a basis for further study of YAB:Mn for the purposes of luminescent thermometry, as well as other applications.