Calibration of local chemical pressure by optical probe.

Chemical stabilization of a high-pressure metastable state is a major challenge for the development of advanced materials. Although chemical pressure ( P chem ) can effectively simulate the effect of physical pressure ( P phy ), experimental calibration of the pressure passed to local structural motifs, denoted as local chemical pressure ( P chem- Δ ) which significantly governs the function of solid materials, remains absent due to the challenge of probing techniques. Here we establish an innovative methodology to experimentally calibrate the P chem- Δ and build a bridge between P chem and P phy via an optical probe strategy. Site-selective Bi 3+ -traced RE VO 4 ( RE  = Y, Gd) is adopted as a prototype to introduce Bi 3+ optical probes and on-site sense of the P chem- Δ experienced by the RE O 8 motif. The cell compression of RE 0.98 Bi 0.02 VO 4 under P phy is chemically simulated by smaller-ion substitution (Sc 3+ → RE 3+ ) in RE 0.98- x Sc x Bi 0.02 VO 4 . The consistent red shift ( Δλ ) of the emission spectra of Bi 3+ , which is dominated by locally pressure-induced RE O 8 dodecahedral variation in RE 0.98 Bi 0.02 VO 4 ( P phy ) and RE 0.98- x Sc x Bi 0.02 VO 4 ( P chem- Δ ), respectively, is evidence of their similar pressure-dependent local structure evolution. This innovative Δλ -based experimental calibration of P chem- Δ in the crystal-field dimension portrays the anisotropic transmission of P chem to the local structure and builds a bridge between P chem- Δ and P phy to guide a new perspective for affordable and practical interception of metastable states.