Unraveling the Charge State of Oxygen Vacancies in Monoclinic ZrO2 and Spectroscopic Properties of ZrO2:Sm3+ Phosphor

Ion beam analysis methods are very sensitive to analyze the defects and impurities in insulators and semiconductors. The present study focuses on an investigation of the nature of defects in monoclinic ZrO2 and spectroscopic properties of ZrO2:Sm3+ (1 mol %) phosphor using ionoluminescence (IL) under the excitation of 100 MeV Si7+ ions. The structures of the combustion-synthesized ZrO2 and ZrO2:Sm3+ samples were revealed to be monoclinic as analyzed through X-ray diffraction, Raman spectroscopy, and selected area electron diffraction methods. Structural parameters were assessed utilizing Rietveld refinement of the obtained XRD data using GSAS II software. The average particle size of ZrO2 and ZrO2:Sm3+ samples was found to be 77 +/- 2 and 72 +/- 3 nm, respectively, as determined from transmission electron microscopy images. The electronic structure and the oxygen vacancy defect population were analyzed using experimental measurements [viz ionoluminescence (IL), photoluminescence (PL), PL lifetime decay, electron paramagnetic resonance (EPR), and diffuse reflectance spectroscopy (DRS)]. The prominent IL and PL emission peaks seen at 499 nm in monoclinic ZrO2 are attributed to the F+ type center that was assigned to the F-2(+) center.an aggregate of the singly ionized oxygen vacancies. ZrO2:Sm3+ (1 mol %) samples display Sm3+ characteristic IL emission peaks between 562-582, 600-620, 635-673, and 719 nm, corresponding to ((4)G(5/2) -> H-6(5/2)), ((4)G(5/2) -> H-6(7/2)), ((4)G(5/2) -> H-6(9/2)), and ((4)G(5/2) -> H-6(11/2)) transitions under 100 MeV Si7+ ion excitation for various fluences. The 100 MeV Si7+ ion-induced ion track radius (damaged cross section) and local temperature were estimated through the thermal spike model to be 0.53 nm and 700 K (the duration is about 10(-13) second), respectively. CIE coordinates fall near the yellow color region and then slightly shift toward the green color region with an increase of fluence because of the lattice distortion and change of the Sm3+ symmetry site.