Effect of Tm ³⁺ Ions on the White Light Emission of Dy ³⁺ – Tm ³⁺ Codoped SrMg ₂ La ₂ W ₂ O ₁₂ Phosphors

Abstract

Dy 3+ – Tm 3+ ions codoped SrMg 2 La 2 W 2 O 12 (strontium magnesium lanthanum tungstate) phosphors were synthesized by conventional high‐temperature solid‐state reaction method. X‐ray analysis of the end products revealed the well‐crystallized phases with orthorhombic structure. The functional groups present in the phosphors were studied by the Fourier transform infrared measurements. To know the potential applicability of these phosphors for white light emission, the excitation and emission spectra were recorded. The excitation spectra exhibited an intense broad band at 313 nm, pertaining to the O → W ligand‐to‐metal charge‐transfer state ( LMCT ) of the host. With the excitation of LMCT band (313 nm), the decay curves of singly doped SrMg 2 La 2 W 2 O 12 : Dy phosphors exhibited single exponential, where as the codoped SrMg 2 La 2 W 2 O 12 : DyTm phosphors exhibited double exponential nature. The luminescence colors of these phosphors were estimated from Commission Internationale de L'Eclairage ( CIE ) coordinates using the photoluminescence data. The color of singly doped SrMg 2 La 2 W 2 O 12 : Dy phosphor has been tuned by codoping with Tm 3+ ions. It has been noticed that the CIE chromaticity coordinates ( x , y ) determined from the luminescence spectrum of singly Dy 3+ doped SrMg 2 La 2 W 2 O 12 phosphor shifted toward the white light region, when codoped with Tm 3+ ions. The increase in correlated color temperatures ( T cct ) has been noticed with the increase of Tm 3+ ions concentration in SrMg 2 La 2 W 2 O 12 : DyTm phosphors.