Spectroscopy of erbium f-f transitions in ErGa3(BO3)4 crystal and dual-mode luminescence cryothermometry at 1.5 μm

Transmission and photoluminescence (PL) spectra of erbium gallium orthohoborate ErGa 3 (BO 3 ) 4 crystal were studied in a broad range of frequencies (5500 – 23,000 cm -1 ) and temperatures (3–300 K). The energies of 47 crystal-field levels of the Er 3+ ion were determined. Luminescence temperature sensors are proposed using two different approaches: measuring (1) the line intensity ratio and (2) the half-width of a spectral line. A total temperature range from 15 to 150 K is covered, with temperature resolution ~ 0.1 K. The relative thermal sensitivities of 7.6 and 0.9% K -1 at 25 and 110 K, respectively, were achieved. The importance of taking into account the processes of reabsorption is emphasized. • 47 Er 3+ crystal-field levels were determined by PL and TRA spectroscopy. • Self-absorption influences 1.5 µm Er 3+ emission intensities in ErGa 3 (BO 3 ) 4 . • Boltzmann LIR thermometry at 1.5 µm: 15–80 K, Sa(max) at 25 K, Sr(25 K) =7.6% K −1 . • Linewidth thermometry at 1.5 µm: 30–150 K, Sr(max) = 0.9% K −1 at 110 K. • Dual-mode readout covers 15–150 K with ~0.1 K temperature resolution.