Study of energy transfer process and radiative properties of CaAl4O7:Ho3+ phosphor for green light emission

Abstract

This work comprehensively analyse the structural and photoluminescence properties of Ho3+-doped CaAl4O7 phosphor systems. X-ray diffraction (XRD), diffuse reflectance spectrum (DRS), photoluminescence (PL), and Fourier transform infrared (FT-IR) spectroscopy measurements were carried out, and Rietveld analysis confirmed the pure monoclinic structure of CaAl4O7:Ho3+ phosphor. The FT-IR spectrum showed absorption bands for the tetrahedral sites of the Al-O bonds and the octahedral sites of the Ca-O bonds, which indicate the formation of the CaAl4O7:Ho3+ phosphor. The diffuse reflectance spectrum shows sharp peaks in the visible and near-infrared regions. Photoluminescence excitation (PLE) measurements were performed on all the phosphor samples by monitoring emissions at 545 nm. Radiative properties such as total radiative transition probabilities (AT), radiative lifetime (τ rad), and branching ratios (β) are reported by Judd–Ofelt analysis and PLE spectral measurements. Upon 454 nm excitation, a green emission band is observed at around 545 nm (5F4 + 5S2 → 5I8), and these results indicate that x = 0.05 mol Ho3+ is the optimum concentration as the 5F4 + 5S2 → 5I8 emission intensity reaches its maximum. The emission intensity quenching and energy transfer mechanism are discussed, and the results suggest that the CaAl4O7:Ho3+ samples are suitable for green-emitting phosphor.