Structural, vibrational and luminescence properties of Nd3+ ions in new Ca4Ln3Nb5O21 (Ln = La0.99Nd0.01, Nd, Gd0.99Nd0.01) niobate – Prospective laser materials

Abstract

Research on the phase equilibria in one of the cross-sections of a CaO–Nd2O3–Nb2O5 ternary oxide system, i.e. the Ca2Nb2O7–Nd3NbO7 binary system, has shown the existence of a new solid solution with the general formula (Ca2Nb2)2xNd3NbO14x+7 (0 < x < 1) and a homogeneity range between Nd3NbO7 and Ca4Nd3Nb5O21 end-members. The dependence of the powder XRD patterns, as well as IR and Raman, emission and excitation spectra and luminescence decay times on mixture composition has been reported. XRD and spectroscopic studies show a continuous change of the substrates’ interaction within the existence limit of a new solid solution. Significant improvement of the luminescence properties was obtained by dilution of the optically active Nd3+ ions by gadolinium and lanthanum in the Ca4Nd3Nb5O21 end-member of the new solid solution. The spectroscopic measurements were used to propose the depopulation mechanism of the Nd3+ electron excited states in the studied materials. The optical band gaps of Ca2Nb2O7, Ca4Nd3Nb5O21 and Nd3NbO7 were calculated using Tauc plots.