Structural characterization and optical thermometric performance of Eu3+doped MgGd2Zr2O8 phosphors

Abstract

This paper reports the synthesis and characterization of a new luminescent material, MgGd2Zr2O8 doped with (2, 5, 10, 15, 20, and 25 at%) Eu3+ ions, and its potential application in optical thermometry. The samples were produced via a facile sol-gel synthesis and subsequently thermally treated for 4 h at 850 °C. An X-ray powder diffraction (XRPD) analysis with Rietveld refinement has revealed that the synthesized samples crystallize in a fluorite-type cubic crystal structure, space group Fm (Formula presented) m, with crystallite sizes of around 7 nm and lattice parameter expansion due to Mg2+ ions preferentially occupying interstitial or vacant sites. Transmission electron microscopy (TEM) has shown that the sample contains randomly shaped aggregates (around 200 nm), formed by the accumulation of many small particles (less than 100 nm). High-resolution TEM revealed the crystalline nature of the sample with lattice planes compatible with the XRPD analysis and crystallite sizes below 10 nm. EDS elemental mapping confirmed the uniform distribution of all elements in the sample. The photoluminescent emission spectra indicated typical energy Eu3+ ion transitions from the 5D0 excited state to the 7FJ (J = 1-4) manifolds. The optimal MgGd2Zr2O8:Eu3+ (15 at%) phosphor exhibited a satisfactory temperature-sensing performance, reaching the maximum relative sensitivity (Sr) of 0.47 % K−1 at 570 K based on the change in the full width at the half maximum (FWHM) of 5D0→7F1 transition (592 nm). A slightly lower value of 0.32 % K−1 was obtained using the luminescence intensity ratio (LIR592/612) between the 5D0→7F1 and 5D0→7F2 transitions. The valley-to-peak ratio (VPR) method showed moderate but stable sensitivity (0.22–0.14 % K−1) across the 300–570 K range, indicating a reliable thermometric behavior over a broad temperature window