Luminescence spectroscopy of Cr³⁺ ions in bulk single crystalline β-Ga₂O₃

Abstract

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 dependences of the luminescence intensity and the decay time of Cr3+ ions indicate the same mechanism of quenching of R-line 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−1 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.

Multimodal Non-Contact Luminescence Thermometry with Cr-Doped Oxides

“…To understand this discrepancy, one needs to bear in mind the quantitative difference in the energy structure of Cr 3+ in this host leading to such changes. The energy gap between the and levels in Ga 2 O 3 is only by about a factor 4 less than the energy difference between the 2 E and 4 T 2 [ 71 , 75 ] whereas, in other crystals of this study, this ratio is more than 25. Because of this, the and levels of Cr 3+ in Ga 2 O 3 cannot be treated as an isolated system at low temperatures.…”

Origin of Red Emission in β‐Ga2O3 Analyzed by Cathodoluminescence and Photoluminescence Spectroscopy

“…In literature, the R peaks at room temperature are at 695 nm (R1) and 688 nm (R2). [ 11 ] At room temperature (290 K), the peak positions of the sharp lines for the UID and Fe‐doped sample are at 693.6 nm and 689.4 nm and thus matched to R1 and R2. The signal to noise is too low for the aforementioned peaks to be observed at room temperature for the Si‐doped sample.…”

“…The origin of the red emission is quite ambiguous, and the literature provides three plausible explanations involving doping by transition metals or rare earth metals [ 10–14,19–21 ] or by nitrogen. [ 22,23 ] Figure 1b shows the CL spectra recorded in the region of 700 nm to provide more details in the near‐IR region of the spectrum.…”

“…The Cr ion is known to emit two well‐defined lines centered at ≈1.78 eV (696.5 nm) and 1.80 eV (688.8 nm), the so‐called R lines due to the 2 E → 4 A 2 electronic‐level transitions. [ 11 ] Figure 3 shows the analysis of the temperature dependence of the two red emission peaks. As shown in Figure 3a, the 688 nm peak intensity increases on cooling from 290 K and reaches a maximum intensity at around 120 K, after which it starts to decrease and eventually vanishes at 10 K. On the other hand, the 695 nm peak (see Figures 3b,d) increases in intensity on decreasing the temperature and reaches a maximum intensity at 10 K. Both peaks red shift in the wavelength as the temperature increases (see Figure 3c).…”

“…The optical properties of β ‐ Ga 2 O 3 grown by various methods with different dopants have been widely reported, [ 5–9 ] primarily for emission in the UV and blue regions of the visible spectrum. However, there are only a few reports [ 10–14 ] on emission in the red spectral region due to transition metals, which is the focus of this work. We discuss red emission in relation to various dopants in β‐Ga 2 O 3 .…”