The spectroscopic quality factor, phase, morphological, structural, and photoluminescent analysis of ZrO<inf>2</inf>:Nd³⁺ coatings created by Plasma electrolytic oxidation

Abstract

15 μm thick ZrO2:Nd3+ coatings were synthesized by the plasma electrolytic oxidation process from the pure zirconium substrate in an alkaline electrolyte with the addition of five different concentrations of Nd2O3 powders. SEM/EDS images show morphologies characterized by numerous pores and cracks, and uniform distribution of coating constituents. XRD revealed that the monoclinic phase is dominant and that Nd impurity stabilizes the tetragonal phase. The average crystalline size is 27.5 nm. XRF revealed a linear increase in incorporated Nd with increasing Nd2O3 concentration. Photoluminescence spectra are characterized by the NIR emissions at typical energies for Nd3+ ion. The highest emission intensity is obtained with 2.0 g/L Nd2O3. The explicit equation for branching ratios in relation to the emission intensities and Judd-Ofelt parameters is recalculated. A novel, more precise equation for the calculation of the spectroscopic quality factor from the most intense emissions is presented. The spectroscopic quality factor is the lowest in the sample with the highest photoluminescent intensity, and is one of the lowest values, in comparison with the 203 spectroscopic quality factors calculated from the Judd-Ofelt parameters in the literature. The luminescence intensity decreases with temperature by the phonon-assisted cross-relaxation mechanism. The luminescence thermometry by the lifetime of 4F3/2 level shows ∼2% K−1 relative sensitivity in the 300–380 K temperature range.