Evolution of phase composition and luminescent characteristics of the La1-x-ySmxCayVO4-δ nanocrystalline phosphor

Abstract

This work aims to clarify the relationship between the optical, particularly luminescent, characteristics of the La_1-x-ySm_xCa_yVO_4-δ powder nanosized compounds with their phase composition and concentration of dopants. According to the high-accuracy XRD data, the samples are a mixture of monoclinic and tetragonal crystal phases. The diffuse reflection and photoluminescence (PL) spectra were measured and analyzed including spectral distributions and intensity ratios of the PL bands, the positions and half-widths of envelopes of the groups of lines in the PL spectra of Sm³⁺ ions. Estimated from the diffuse reflection data the band gap values are 3.85, and 3.82, 3.75, 3.78 eV for the samples with x = 0.1, y = 0, and (x, y) = 0.05, 0.10, 0.15, respectively. The PL excitation spectra of the La_1-x-ySm_xCa_yVO_4-δ nanoparticles consist of both the wide UV wavelength band (260–360 nm) caused by transition in the VO₄³⁻ molecular groups and in a set of narrow lines caused by inner f-f transitions in the Sm³⁺ ions (spectral range 350–520 nm). The PL spectra of the La_1-x-ySm_xCa_yVO_4-δ nanoparticles contain four groups of lines (I – IV) resulting from the ⁴G_5/2 → ⁶H_5/2, ⁶H_7/2, ⁶H_9/2, and ⁶H_11/2 transitions, respectively, in the inner f shell of the Sm³⁺ ions. The concentration behavior of the Sm³⁺ ions PL characteristics is related to the evaluation of the phase composition of La_1-x-ySm_xCa_yVO_4-δ samples. It was found that the changes of the R_lum = I_(III)/I_(I), where I_(III) and I_(I) are the integrated intensities of the corresponding groups of lines, can be related to the phase composition of the La_1-x-ySm_xCa_yVO_4-δ compounds. Developed in this work the combined way of structural and optical data analysis may be useful in designing other multiphase phosphor systems containing Sm³⁺ ions.