Size and shape-tailored hydrothermal synthesis and characterization of nanocrystalline LaPO₄:Eu³⁺ phosphor

Highlights: • Distinct spherical and rod-like like morphology by hydrothermal method. • Tailored the morphology of LaPO₄:Eu³⁺ crystals at different pH values. • The impact of shape anisotropy on their photoluminescence properties revealed. - Abstract: A facile hydrothermal route has been demonstrated for the synthesis of Eu³⁺ doped LaPO₄ with distinct and well-controlled morphologies (spherical and rod-like). Morphological control has been established by fine-tuning the pH of the precursor solution, and formation of different morphologies at different pH values has been explained by taking into consideration the chemical potentials of the various species present in the precursor solution. At constant pH of the mother liquor, an increase in the autoclaving temperature from 120 °C to 140 °C is seen to change the aspect ratio of the nanorods. A red shift in the charge transfer band is observed in the excitation spectra of the nanocrystalline samples (both nanorod and nanosphere) with respect to the bulk. A change in the (red/orange) peak intensity ratio in the photoluminescence emission spectra of bulk, spherical and rod-like nanocrystalline samples reveals that the host morphology plays a vital role in determining the local symmetry of Eu³⁺ in LaPO₄ matrix. Decay-time measurement of the as-prepared morphologies at 620 nm (for ⁵D₀–⁷F₂ transition) leads to a maximum value for nanorods (3.7 ms), while the corresponding values for nanospheres and bulk samples are somewhat smaller (2.58 ms and 2.99 ms respectively). This clearly indicates the influence of shape anisotropy on the photoluminescence properties of the as-synthesized nanoarchitectures.