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-) 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- and build a bridge between P_chem and P_phy via an optical probe strategy. Site-selective Bi³⁺-traced REVO₄ (RE = Y, Gd) is adopted as a prototype to introduce Bi³⁺ optical probes and on-site sense of the P_chem- experienced by the REO₈ motif. The cell compression of RE_0.98Bi_0.02VO₄ under P_phy is chemically simulated by smaller-ion substitution (Sc³⁺ → RE³⁺) in RE_0.98-ScBi_0.02VO₄. The consistent red shift (Δλ) of the emission spectra of Bi³⁺, which is dominated by locally pressure-induced REO₈ dodecahedral variation in RE_0.98Bi_0.02VO₄ (P_phy) and RE_0.98-ScBi_0.02VO₄ (P_chem-), respectively, is evidence of their similar pressure-dependent local structure evolution. This innovative Δλ-based experimental calibration of P_chem- in the crystal-field dimension portrays the anisotropic transmission of P_chem to the local structure and builds a bridge between P_chem- and P_phy to guide a new perspective for affordable and practical interception of metastable states.