Novel Dy3+ -doped CaYF5 phosphor: Structural and optical properties for solid-state lighting applications

Abstract

In this work, Ca_(1-x) YF₅: xDy³⁺ (x = 1 to 3 mol% in steps of 0.5) phosphors were synthesized via the chemical co-precipitation technique. XRD analysis confirmed that both doped and undoped samples exhibit a consistent face-cantered cubic (FCC) phase with an Fm-3m space group, further validated by Rietveld refinement. SEM and EDX were employed to analyse the structural features and chemical composition of the prepared phosphor, respectively. FTIR spectroscopy was employed to identify chemical bonding and corresponding vibrational modes. DRS technique was utilized to estimate the energy band gap (E_g = 5.60 eV for pure CaYF₅ and E_g = 6.34 eV for CaYF₅:2mol% Dy³⁺), as well as optical parameters, such as the refractive index (RI = 1.92 for pure CaYF₅ and n = 1.83 for CaYF₅: 2 mol% Dy³⁺).Moreover, we found that the Dy³⁺-ligand bond in the CaYF₅ phosphor host is primarily ionic in nature. Photoluminescence (PL) studies revealed a primary excitation peak at 353 nm, corresponding to the ⁶H_15/2 $\to$⁶P_7/2 transition. The emission spectra exhibited four distinct peaks at 481(blue) nm,491 nm(blue), 579 nm (yellow), and 673 nm (red), corresponding to Dy³⁺ ion transitions ⁴F_9/2 $\to$⁶H_j, (J = 15/2,13/2,11/2). Based on Dexter's theory we observed luminescence quenching occurred at 2 mol% of Dy³⁺, which is due to dipole-quadrupole interactions. The optimized phosphor sample exhibited key characteristics such as CIE (0.4829, 0.4907), and CCT ($\sim$ 2950 K), and high colour purity (92.2 %). Furthermore, TDPL studies demonstrated excellent thermal stability, showing consistent luminescence across different temperatures. The calculated activation energy of 0.1564 eV and corresponding CIE reveals slight change in wavelength observed at high temperature (578.4 nm at 298 K to 577.4 nm at 498 K). It highlights its potential for solid-state lighting applications.