White light generation in Dy3+-doped fluorosilicate glasses for W-LED applications

Abstract

Dysprosium doped fluorosilicate (SNbKZLF:SiO₂-Nb₂O₅-K₂O-ZnF₂-LiF) glasses have been prepared and studied through excitation, emission and decay rate analysis. Sharp emission peaks were observed at 485 nm (blue) and 577 nm (yellow) under 387 nm excitation, which are attributed to ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions, respectively, of Dy³⁺ ions. The yellow-to-blue intensity ratio increases (0.85 to 1.19) with increase in Dy³⁺ ion concentration. The decay rates exhibit single exponential for lower concentrations and turns into non-exponential for higher concentrations. The non-exponential nature of the decay rates are well-fitted to the Inokuti-Hirayama model for S = 6, which indicates that the nature of the energy transfer between donor and acceptor ions is of dipole-dipole type. The lifetime for the ⁴F_9/2 level of Dy³⁺ ion decreases (0.42 to 0.14 ms), whereas energy transfer parameter increases (0.11 to 0.99) with increase of Dy³⁺ ion concentration (0.05 to 4.0 mol %). The chromaticity coordinates have been calculated from the emission spectra and analyzed with Commission International de I'Eclairage diagram. The chromaticity coordinates appeared in the white light region for all concentrations of Dy³⁺ ions in the present glasses. The correlated color temperature value decreases from 5597 K (closer to the day light value of 5500 K) to 4524 K with increase of Dy₂O₃ ion concentration from 0.01 to 4.0 mol %. These results indicate that Dy³⁺:SNbKZLF glasses can be considered as a potential host material for the development of white light emitting diodes.