Nano-synthesis and characterization of Er3+, Ho3+ and Li+ co-doped, Er3+ and Li+ co-doped and Ho3+ and Li+ co-doped lanthanum borosilicate luminescent materials (LaBSiO5) by a sol–gel pyrolysis method for forensic applications

Abstract

In the present investigation, lanthanum borosilicate nanomaterials doped with Er³⁺/Ho³⁺ and co-doped with Li ⁺or both Er³⁺ and Ho³⁺ co-doped with Li⁺ are synthesized using a sol–gel pyrolysis method, taking urea as an organic precursor. The samples are found to be phase pure from the XRD data, analysed using an X’pert high score software. All the samples are found to have a single-phase stillwellite structure with hexagonal symmetry. The unit cell dimensions are a = b = 6.870, c = 6.6964, V = 274.26, in accordance with the P3₁ space group. From the SEM studies, it is observed that spherical agglomerated particles are formed. The agglomeration is found to be more in Er³⁺/Ho³⁺ and Li⁺ co-doped samples than in Er³⁺, Ho³⁺ and Li⁺ co-doped samples. The agglomerated particle size is found to be in the range of 0.25 μm to 0.80 μm. From the HRTEM selected area diffraction pattern studies and XRD patterns, using the Debye Scherer formula, the crystallite sizes are calculated, which showed the formation of nanoparticles. The synthesized samples emitted in the blue-to-violet region when exposed to a long-range UV lamp and emitted in the orange-red region when exposed to a short-range UV lamp. The photoluminescence spectra showed the presence of two different cationic sites, and the intensities of the spectra are found to be more in the Er³⁺, Ho³⁺ and Li⁺ co-doped samples than in the Er³⁺/Ho³⁺, Li⁺ co-doped samples, indicating that the emission from the co-dopants followed a carrier energy transfer model. The fingerprints recorded on different materials using the synthesized phosphors shed light on the usefulness of the phosphors for forensic latent fingerprint detection.