Madhab Pokhrel

Synthesis of green phosphors from highly active amorphous silica derived from rice husks

In this work, high purity amorphous silica derived from rice husk (RH) biomass was used to prepare green phosphor (Zn2SiO4:Mn2+). Based on the solid phase reaction under high temperature, the optimum doping concentration and reaction temperature were identified. The overall performance in terms of photoluminescence intensity and quantum yield of the RH-derived phosphor was superior to the one derived from commercial silica and close to the one made from silicic acid. The results showed that the phosphor derived from RH silica could serve as an alternative to commercial phosphor because of its decent properties and inexpensive green resource.

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

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.