Equivalent cation substitution-triggered highly efficient Mn4+ red emission in double-perovskite type (Ba, Sr)2(Gd, La, Y, Lu)(Nb, Sb)O6:Mn4+ solid solution phosphors and photophysical studies

Abstract

Double-perovskites have attracted worldwide attention for the encapsulation of Mn4+ in far-red luminescence application. But the limited quantum yield and low-stability to thermal quenching have inevitably blocked their practical uses. Herein, the compositional adjustments including [Sr2+→Ba2+], [Y3+/La3+/Lu3+→Gd3+] and [Sb5+→Nb5+] equivalent cation substitution are employed. Such simple strategy can efficiently improve emission intensity and thermal stability of (Ba, Sr)2(Gd, La, Y, Lu)(Nb, Ta)O6:Mn4+ solid solution phosphors with double-perovskite structures. The optical change performance has been evaluated by variation in lattice structure and theoretical calculations. X-ray diffraction patterns and Rietveld refinement results reveal that perfect crystalline phase in terms of the same double-perovskite structure of Ba2GdNbO6 with cubic Fm-3 m space group can be formed at a high Y3+/Lu3+-doping (0 ≤ y ≤ 1.0) and Sb5+-doping (0 ≤ z ≤ 0.7) substitution ratio. Simultaneously, the incorporation of Sr2+ and La3+ will only keep the solid solution phase at a low substitution ratio at 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.3, respectively. The most significant increase of emission intensity in Sr2+-Lu3+-Sb5+ co-substituted case can reach as high as 291%. Its excellent stability to thermal quenching at LED working temperature is observed and the intensity has been elevated to 148.3%-198.7% across the 423–473 K relative to the unsubstituted sample. A slight wavelength-shift of Mn4+ is monitored in diverse cation-substituted samples and such fact is caused by the doping-induced alteration of Mn4+ local environments, which can be illuminated adequately by Tanabe–Sugano diagram. Based on packaging the composition-optimized phosphor onto a blue LED chip, a proof-of-concept LED device has been afforded. Its electroluminescence spectrum not only matches well with the absorption profiles of natural plants, but also exhibits high stability to different currents, which will be very favorable in the domain of high-power plant growth LEDs. The concept of cation-substitution in guiding design for cultivation purpose will open a new way in related optoelectronic devices.