MECHANISM OF PHOTOLUMINESCENCE AFTER PHYSICS AND CHEMISTRY OF HARD CONDENSED DECOMPRESSION MATTER, EARTH SCIENCES SYNCHROTRON SOLEIL HIGHLIGHTS 2020 Under pressure the LP pyrochlore phase transformed to the HP cotunnite phase at 32.3 GPa in HoSnO. The increasing crystal field2 2 7 splitting between the t2gand e causes the strong hybridization of 4fg ODE BEAMLINE and 5d orbitals at the HP phase in Fig.3ab. Upon releasing pressure, the HP phase transforms to the coexistence of an amorphous and defect-cotunnite phase. The local Hosite symmetry breaks down3+ Associated publication sequentially from D to C then C , and nearest coordination change3d 1 Tricolor Ho photoluminescence3+ s accordingly. The pristine non-PL character in HoSnO is popular as enhancement from site symmetry 2 2 7 breakdown in Pyrochlore HoSnO typically Ln doped materials show PL spectrum with doping limitation3+ 2 2 7 up of 1%. Tricolor PL (S-center) is successfully generated once the LP- after pressure treatment. HP phase transition starts and the site symmetry breakdown from D3d Y. Zhao, K. Chen, N. Li, S. Ma, Y. Wang, to C seen in Fig.3c. Decompression-induced amorphization reduces Q. Kong, F. Baudelet, X. Wang & s Ho site symmetry further down to C , which enhances the ion pair3+ W. Yang. cross-relaxation process and provides an additional emission center (L1 center) for the F →I transition and promotes the minority red-PL to5 5 Physical Review Letters, 125, 5 8 art.n° 245701 (2020). dominant among the tricolor PL. With compression below 29.0 GPa, the quenched sample shows no PL change, which can be used as a pressure history detector for an extreme environment. References FIGURE 3 [1] B. Wu, et al. , Rare Met. Cement. Carbides 25, 549 (2006). [2] C. Gong et al., J. Phys. Chem. C 118, 22739 (2014). [3] W.M. Yen et al., Phosphor Handbook (CRC press, Boca Raton, FL, 2006). [4] Y. Zhao et al., J. Phys. Chem. C 120, 9436 (2016). [5] Y. Zhao et al., Adv. Mater. 29, 1701513 (2017). Captions FIGURE 1: (a) PL spectra of Ho2Sn2O7 duringcompression and (b) decompression. (c) The separated three PL intensity fractions and (d) total PL intensity with pressure. FIGURE 2: (a) The second derivative of XAS measured under various pressures. The inset shows the energy CONCLUSION gap ΔEg with pressure. (b) Energy gap ΔEg variation withpressure. (c) The relative intensity of [(eg - t2g'(t2g)] with The insight for this work includes: pressure. 1) pressure as a great tuning tool is used to turn a non-PL material to a FIGURE 3: The 5d orbital energy gap ΔEg of Ho ions3+ multi-color PL at well exceeding doping limitation level (18.2% vs. 1%); between eg and t2g'(t2g) at LP phase (a) and HP phase (b). 2) pressure treated HoSnObecomes a mixture of high pressure (c) Energy level diagram ofHo under decompression,3+ 2 2 7 two emission centers of S-center and L-center are cotunnite and amorphous phases, which enables a dual-emission center, presented respectively. and turn the minority red-emission (F to I5 585 deexcitation) to dominant among the three color emissions; 3) the underline mechanism can be well explained by the XRD structural, XAS spectroscopy and PL spectrum analysis. Our findings highlight the role of the pressure effect on HoSnO, the reserved and enhanced2 2 7 tricolor PL can serve as the extreme condition history detector and improve bioluminescence imaging technology. Our study highlights the pressure effect on the local ion site symmetry, which largely turns and enables the new emission center from traditionally less than 1% doping level of RE ion materials to a regular site RE (18% in this case). 71