Exploring the optical properties of La2Hf2O7:Pr3+ nanoparticles under UV and X-ray excitation for potential lighting and scintillating applications

Abstract

New optical materials with efficient luminescence and scintillation properties have drawn a great deal of attention due to the demand for optoelectronic devices and medical theranostics. Their nanomaterials are expected to reduce the cost while incrementing the efficiency for potential lighting and scintillator applications. In this study, we have developed praseodymium-doped lanthanum hafnate (La₂Hf₂O₇:Pr³⁺) pyrochlore nanoparticles (NPs) using a combined co-precipitation and relatively low-temperature molten salt synthesis procedure. XRD and Raman investigations confirmed ordered pyrochlore phase for the as-synthesized undoped and Pr³⁺-doped La₂Hf₂O₇ NPs. The emission profile displayed the involvement of both the ³P₀ and ¹D₂ states in the photoluminescence process, however, the intensity of the emission from the ¹D₂ states was found to be higher than that from the ³P₀ states. This can have a huge implication on the design of novel red phosphors for possible application in solid-state lighting. As a function of the Pr³⁺ concentration, we found that the 0.1%Pr³⁺ doped La₂Hf₂O₇ NPs possessed the strongest emission intensity with a quantum yield of 20.54 ± 0.1%. The concentration quenching, in this case, is mainly induced by the cross-relaxation process ³P₀ + ³H₄ → ¹D₂ + ³H₆. Emission kinetics studies showed that the fast decaying species arise because of the Pr³⁺ ions occupying the Hf⁴⁺ sites, whereas the slow decaying species can be attributed to the Pr³⁺ ions occupying the La³⁺ sites in the pyrochlore structure of La₂Hf₂O₇. X-ray excited luminescence (XEL) showed a strong red-light emission, which showed that the material is a promising scintillator for radiation detection. In addition, the photon counts were found to be much higher when the NPs are exposed to X-rays when compared to ultraviolet light. Altogether, these La₂Hf₂O₇:Pr³⁺ NPs have great potential as a good down-conversion phosphor as well as scintillator material.