Abnormal Pressure-Induced Photoluminescence Enhancement and Phase Decomposition in Pyrochlore La2Sn2O7

La₂Sn₂O₇ is a transparent conducting oxide (TCO) material and shows a strong near-infrared fluorescent at ambient pressure and room temperature. By in situ high-pressure research, pressure-induced visible photoluminescence (PL) above 2 GPa near 2 eV is observed. The emergence of unusual visible PL behavior is associated with the seriously trigonal lattice distortion of the SnO₆ octehedra, under which the Sn–O1–Sn exchange angle θ is decreased below 22.1 GPa, thus enhancing the PL quantum yield leading to Sn ³P₁¹S₀ photons transition. Besides, bandgap closing followed by bandgap opening and the visible PL appearing at the point of the gap reversal, which is consistent with high-pressure phase decomposition, are discovered. The high-pressure PL results demonstrate a well-defined pressure window (7–17 GPa) with flat maximum PL yielding and sharp edges at both ends, which may provide a great calibration tool for pressure sensors for operation in the deep sea or at extreme conditions.

Under ambient conditions, La₂Sn₂O₇ shows a strong near-infrared (NIR) photoluminescence (PL). Starting from 2 GPa, pressure-induced visible PL appears while the bandgap reverses direction (starts increasing after an initial decrease) and reaches a near-flat maximum between 7 and 14 GPa with consumption of NIR PL. The well-defined visible-PL pressure window provides a great calibration tool for pressure sensors under extreme conditions.

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