Validity of Judd-Ofelt spectroscopy based on diffuse reflectance spectrum and fluorescence lifetime of phosphor

Validity of Judd-Ofelt spectroscopy based on measured diffuse reflectance spectrum and fluorescence lifetime of a purely radiative electronic transition of rare-earth-ion in a powder material has been demonstrated. Two representative powder samples of Er³⁺-doped LiNbO₃ and Er³⁺/Yb³⁺-codoped NaYF₄, which have considerably different phonon energies, 880 and 380 cm⁻¹, respectively, have been exemplified to demonstrate the validity. First, diffuse reflectance spectrum was measured for each powder sample and relative absorption spectrum was calibrated from it using Kubelka-Munk relation. Second, fluorescence lifetime of purely radiative 1.5 μm emission of Er³⁺ was measured and absolute absorption cross-section spectrum was calibrated on the basis of the assumption that the measured 1.5 μm fluorescence lifetime equals the radiative lifetime. Finally, the Judd-Ofelt parameters Ω_t (t = 2, 4, 6) are calculated on the basis of the absolute absorption cross-section spectrum. For comparison, Judd-Ofelt analysis was also performed on the Er³⁺-doped LiNbO₃ single-crystal on the basis of the absorption spectrum obtained from Beer-Lambert law. The Ω_t result of Er³⁺-doped LiNbO₃ powder sample is compared with that of single-crystal state. The comparison shows that the Ω_t result of the powder sample can be considered as the same as that of the single-crystal state within the error, confirming the validity of the method. The study on the Er³⁺/Yb³⁺-codoped NaYF₄ microcrystal powder allows us to reach the same conclusion.