4 tional to the absorption coefficient. Furthermore, the agreement between TEY and the IPFY in our samples suggests that the MARPE effect is insignificant, at least at the Cu L and Nd M edges of LNSCO. µ$_{s}$ are the thickness and absorption coefficient the con- taminated surface, respectively (i.e., for d thin relative to the x-ray penetration depth). A limitation of this technique is that it requires a detec- tor with minimal background (dark counts) and sufficient energy resolution to separate the NXES from RXES. In our test case of the Cu L and Nd M edges of Nd-doped LSCO, both of these criteria are satisfied with a commer- cially available silicon drift detector which has negligible dark counts and an energy resolution of ∼ 100 eV. Even this crude energy resolution is sufficient to clearly sepa- rate the O K NXES from Cu L or Nd M RXES. However, a similar measurement probing the La M edge (3 d to 4 f ) absorption (not shown) in the same material by measur- ing the O K IPFY provides a distorted spectrum due to finite energy resolution of the detector. In this case, La 4 s to 3 p emission ( M$_{ζ}$ ) at ∼ 630 eV results in RXES counts at the O K emission energy of ∼ 525 eV due to the finite energy resolution of the detector. This complica- tion can be circumvented by using detectors with higher energy resolution, such as high-resolution spectrometers used in RXES measurements 13 or, in principle, by using fitting procedures to separate the NXES and RXES. Finally, the energy-resolved fluorescence measurements shown in Fig. 1 highlight an additional difficulty with traditional TFY measurements besides self-absorption ef- fects. In LNSCO, for example, a sizable contribution to the TFY near the Cu L and Nd M absorption edges is due to normal emission from other elements such as the O K and La M emissions, which dip near the absorp- tion edges. This can lead to significant distortions of the spectra that may be larger than any self-absorption ef- fects and can complicate the use of self-absorption correc- tion methods for TFY which are nonetheless appropriate for PFY. 7,8 Furthermore, depending on sample geometry, elastic scattering or specular reflection from the sample can unintentionally contribute to PFY or TFY, but will not contribute to IPFY. In conclusion, we have demonstrated IPFY as an alter- native measure of XAS that can be both bulk sensitive and free of self-absorption effects. IPFY uses normal x- ray emission from an element or core-hole excitation that is different than the x-ray absorption edge being probed. The inverse of the emission spectra is found to be pro- portional to the x-ray absorption coefficient, µ ( E$_{i}$ ). This technique should be generally applicable to a wide range of x-ray absorption measurements using either hard or soft x-rays. Our IPFY method differs from past PFY measure- ments that rely on RXES from the element being investi- gated by the incident photon energy, either as a means to study dilute concentrations of an element 6 or to provide energy resolution enhanced XAS. 14 In both instances, as with TFY, self-absorption effects may occur in the spec- tra since µ$_{X}$ ( E$_{i}$ ) enters as both the rate at which core holes are created and as a factor in the x-ray penetration depth into the sample [as a contribution to µ$_{tot}$ ( E$_{i}$ )]. If µ$_{X}$ ( E$_{i}$ ) is a sizable fraction of µ$_{tot}$ ( E$_{i}$ ), the measured spectra will be distorted relative to the object of inter- est, µ ( E$_{i}$ ). 7,8 Limited measurements of the NXES PFY have been performed in the past as means to investi- gate potential multi-atom resonant photoemission effects (MARPEs), 15,16 however, these previous measurements fail to make the connection that the IPFY is propor- We gratefully thank G. A. Sawatzky for valuable dis- cussions. This work was supported by NSERC. The research described in this paper was performed at the Canadian Light Source, which is supported by NSERC, NRC, CIHR, and the University of Saskatchewan. ACKNOWLEDGMENTS 59 , 6421 (1999). 1 F. deGroot and A. Kotani, Core Level Spectroscopy of Solids (CRC Press, Boca Raton, FL, 2008). 2 J. St¨ ohr, NEXAFS Spectroscopy (Springer, New York, 1996). 3 F. M. F. de Groot, J. Electron. Spectrosc. Relat. Phenom., 67 , 529 (1994). 4 H. Wende, Rep. Prog. Phys., 67 , 2105 (2004). 5 W. 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