Data for: Use photoluminescence of Cr3+ as a local probe for order-disorder transition process in MgAl2O4 spinel
Photoluminescence (PL) spectra of natural Cr3+ doped MgAl2O4 spinel from Tanzania were taken during its order disorder transition (ODT) process. Samples were changed their disordered degree by heating and annealing treatment. PL spectra were taken at the liquid nitrogen (LN) temperature (~77 K) using a 532 nm laser excitation. Spectra from different states were compared with each other and R-line and N-line ratio was used to illustrate the disordered degree of spinel during ODT process. The data fully displayed the details of the spectral variation with high quality. It can be used as a reference for other similar researches, such as spinel PL characterization, ordered degree of synthetic spinel single crystal or ceramics materials, thermal history of spinel, and non-destructive identification of natural and heated spinel gemstones. The PL spectrum of gem-quality MgAl2O4: Cr3+ spinel, origining from Tanzania, was collected and reported in detail (Figure 1). The PL spectrum of natural MAS consisted of two main parts: zero-phono lines (ZPL) and phonon-sidebands (PSB), located in the range of 14640 cm-1 to 14490 cm-1 and 14490 cm-1 to 13700 cm-1 respectively (Figure 1). The ZPL corresponds to the 2E → 4A2 transitions of Cr3+ located in the octahedral coordination; the PSB is caused by a similar mechanism assisted by phonon [1,2]. In ZPL range, four R lines and five N lines were obtained, their positions were listed in Table 1. In the temperature range 0 - 825 ºC, the R peaks were the strongest peak of PL spectra. With the temperature increasing, R1, R1’, R2, and R2’ peaks became broad and finally merged into two peaks. In this process, the peak gradually increased, but the N1 almost remained unchanged (Figure 2). At high temperature, all the PL peaks broaden and merged into a band, and variations were hardly detectable. The maximum value of this band located in the N peak range and the R peaks intensity decreased significantly showing as shoulders. We also noticed that one unknown peak appeared and increased between ZPL and PSB zones (at 1450 cm-1) with temperature increasing in high-temperature range (Figure 3).