Sm3+-doped oxygen-rich AlN film: Probing luminescence thermometry and evidencing energy transfer via Sm-O pairs

Golovynskyi, S., Zhang, F., Luo, J., Datsenko, O. I., Kravchenko, V. M., Sang, W., Jiang, M., Sun, Z., Li, B., Jin, L., Peng, D., & Wu, H. (2024). Sm3+-doped oxygen-rich AlN film: Probing luminescence thermometry and evidencing energy transfer via Sm-O pairs. Journal of Alloys and Compounds, 177365. https://doi.org/10.1016/j.jallcom.2024.177365

Photoluminescence (PL) of a Sm3+-doped (~ 0.2 at%) AlN thin film is studied and compared to an undoped film. Being deposited by radio frequency magnetron sputtering, the films demonstrate a high-quality surface morphology, good crystallinity and even elemental distribution, although they appear to be oxygen-rich (AlN0.9O0.1). The Sm3+-doped film emits a bright orange-red light at UV excitation. In the PL spectrum, a set of line bunches characteristic of Sm3+ is found: the most intense ones at 580, 621 and 660 nm are identified to be due to radiative transitions from the excited Sm3+ level 4G5/2 to the ground ones 6H5/2, 6H7/2 and 6H9/2, respectively. The PL excitation spectrum, being a broad band below 270 nm with shoulders at ~ 280–330 and 330–390 nm, demonstrates no characteristic lines of resonant Sm3+ pumping. So, the rare-earth PL is sensitized by AlN-O defects and oxygen centers or Sm3+-O2– pairs as excitation donors via nonradiative energy transfer. The theoretical calculations of the density of states confirm the existence of Sm3+-O2– pairs and O-related bandgap narrowing. The Sm3+ PL emission has a two-component kinetics with a Sm3+ lifetime of ~ 2 ms, while the component ratio evidences a significant effect of nonradiative processes. Temperature-dependent PL reveals a thermal quenching considered within the model of a charge transfer into the host. The Sm3+ emission lines are examined in terms of applicability to optical thermometry by the fluorescence intensity ratio technique. Considering ratios between integral intensities of the Sm3+ line bunches in the mentioned range, we have found the maximum absolute and relative sensitivities to be ~ 1.3 × 10􀀀 3 and 1.9 × 10􀀀 3 K–1, respectively.