Luminescence properties related to energy transfer process and cross relaxation process of Y2O3: Yb3+/Er3+ thin films doped with K+ ion

In this paper, K+ ion-doped Y2O3: Yb3+/Er3+ luminescent films were prepared using the sol-gel method. The structures of the films were studied using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. A series of high-quality thin films with good crystallization were prepared. The effect of K+ ion doping on the light emission of the samples was investigated. With increasing K+ doping concentration, initially, the lattice was compressed and then stretched. For the undoped samples, the main light emission bands were green and red emissions attributed to Er3+: 2H11/2(4S3/2) -> 4I15/2 and Er3+: 4F9/2 -> 4I15/2, respectively, both of which are two-photon processes, accompanied by weak purple emission attributed to Er3+: 2G7/2 -> 4I15/2, which is a three-photon process. Compared with the undoped sample, the emission attributed to three-photon process may be eliminated by using K+ doping, and the green and red emission intensity may be increased by factors of 2.39 and 2.51 with increasing K+ ion doping, respectively. With the increase in K+ ion doping, the changes in active luminescent centers and distance between rare earth ions were analyzed, and the effect of the process energy transfer (ET) process and cross relaxation (CR) attributed to those on light emission was discussed.