Sol-gel synthesis and up-conversion luminescence of GdPO₄–Gd₃PO₇:Yb³⁺, Ln³⁺ (Ln = Er, Ho, Tm) phosphor

This work reports the structural, morphological and luminescent properties of GdPO₄–Gd₃PO₇:Yb³⁺, Ln³⁺ (Ln = Er, Ho, Tm) phosphors which have been synthesized by Pechini sol-gel process. The XRD patterns indicated that all the samples are crystalline and have a mixture of monoclinic monazite and monoclinic phases. Some samples were synthesized with ammonium hydroxide (NH₄OH) and had better crystallinity than these synthesized without NH₄OH. The up-conversion emissions were obtained under excitation at 967 nm. According to our results, the color emission was tuned from red to green by increasing the Yb³⁺ concentration from 5 mol% to 20 mol%. Moreover, the use of NH₄OH to synthesize the samples doped with 20 mol% of Yb³⁺ enhanced their green emission band ≈3 times. The results reveal that doping the GdPO₄–Gd₃PO₇ particles with rare earths produce an up-conversion emission which can be useful for the fabrication of luminescent coatings or lighting devices.