Luminescence spectroscopy of Cr 3+ ions in bulk single crystalline β-Ga 2 O 3

Detailed investigations of the spectroscopic properties of Cr3+ ions in β-Ga2O3: 0.05% Cr3+ single crystals grown by the floating zone technique have been performed in the temperature range 4.5–550 K. The luminescence of Cr3+ ions at low temperatures is due to narrow R-lines (2E → 4A2 transitions) and their vibronic sidebands, whereas the broad intense band (4T2 → 4A2 transition) dominates at temperatures above 200 K. The vibronic sidebands of R-lines with amplitude of less than 5 % of the R1 line at a temperature of 4.5 K cover the region of 700-735 nm. The temperature dependencies of the luminescence intensity and the decay time of Cr3+ ions indicate the same mechanism of quenching of R-lines intensity and shortening of lifetime for 2E of Cr3+ ions. The temperature dependence of the R1-line decay time of β Ga2O3: Cr3+ with maximal temperature coefficient │Δτ/ΔT│ = 0.023 ms/K at 120 K and maximal specific sensivitity │(Δτ/ΔT)τ-1│ = 0.017 K-1 at 160 K indicates an application potential of this phosphor for low-temperature fluorescence thermometry.