Enhanced luminescence and negative thermal quenching in Bi3+/Tb3+ Co-doped KYF4 green phosphor

Abstract

Despite the broad application of phosphors in lighting technologies, they still face considerable limitations in thermal stability. A novel green-emitting KYF₄:Tb³⁺,Bi³⁺ phosphor was successfully synthesised via a hydrothermal approach, exhibiting superior photoluminescence performance and enhanced thermal stability. The material achieved an absolute photoluminescence quantum yield of 59.74 %. The incorporation of Bi³⁺ ions enabled efficient energy transfer to Tb³⁺ centres, resulting in a 1.5-fold increase in green emission compared to the Tb³⁺-only doped sample. Thermoluminescence and activation energy analyses revealed that Bi³⁺/Tb³⁺ co-doping introduced deeper trap states, increased trap concentration, and a higher thermal activation energy (E_a = 0.47 eV), all contributing to improved thermal stability. Notably, the phosphor maintained nearly constant emission intensity at temperatures up to 443 K. Furthermore, prototype white light-emitting diodes fabricated using the synthesised phosphor exhibited high-quality white light emission under a 10 mA driving current, characterised by an excellent correlated colour temperature and a suitable colour rendering index for lighting applications. These findings demonstrate that Bi³⁺ co-doping is an effective strategy for enhancing both luminescence efficiency and thermal stability in rare-earth-based phosphors, offering valuable insights for the development of advanced solid-state optical materials.