Enhanced dual mode luminescence via energy transfer in Er3+, Yb3+ co-doped β-spodumene

Fundamental understanding of the Stokes and anti-Stokes emissions in luminescence materials and their mechanism is very important for different technological applications. In this article, we report the dual mode, down/upconversion (DC/UC), luminescence in a LiAlSi2O6 (beta-spodumene) single host along with its mechanistic investigations. A series of emission tunable Li1-xAlSi2O6:xEr(3+) (LAS:xEr(3+); 0 <= x <= 0.07) and Li0.99-yAlSi2O6:0.01Er(3+),yYb(3+) (LAS:0.01Er(3+),yYb(3+); 0.001 <= y <= 0.007) phosphor powders were prepared by solid state reaction method at 1300 degrees C. The formation of single-phase phosphors is verified by XRD technique and other structural properties are investigated by FT-IR, UV-Vis-NIR spectra. The phosphors produced NIR DC emission at 1535 nm (under 380 and 980 nm excitation) and an intense red UC emission at 655 nm (under both 980 and 808 nm excitations). The dual mode emission intensity of the LAS:0.01Er(3+) is further improved by co-doping Yb3+ ions via energy transfer from Yb3+ to Er3+. The red UC emission intensity of LAS:0.01Er(3+),0.005Yb(3+) phosphor under 980 nm excitation is similar to 10 times stronger than the singly doped LAS:0.01Er(3+) phosphor. In addition, the phosphors can also be efficiently excited by 808 nm laser and hence can be used for biological application since 808 nm NIR irradiation exhibits higher light penetration depth without inducing overheating. The mechanism of energy transfer from Yb3+ to Er3+ by considering different emission pathways viz: ground state absorption (GSA), excited state absorption (ESA), energy transfer upconversion (ETU), back energy transfer (BET) and cross relaxation (CR) are discussed in detail. Based on the dual mode emissions, the LAS:xEr(3+) and LAS: xEr(3+),yYb(3+) (x = 0.1 and 0.001 <= y <= 0.007) phosphors could be a potential candidate not only for the biological application as bio-probe but also as energy convertors for solid-state lighting, displays, and solar cell applications. (C) 2021 Elsevier B.V. All rights reserved.