Tuning of structural, laser power-dependent and temperature dependent luminescence properties of NaYF4:Yb, Er (Y: 88%, Yb: 10 and Er: 2%) submicron crystals using Cr3+ ion doping

Abstract

In this work, we show the influence of Cr3+ ion concentration (1–7 mol%) on the crystalline phase and shape, laser power dependent luminescence response, and temperature response in physiological temperature range for NaYF4:Yb, Er (Y: 88%, Yb: 10% and Er: 2%) submicron crystals prepared via hydrothermal method. The atomic absorption spectral studies indicate the successful incorporation of the Cr3+ ions into NaYF4:Yb, Er (Y: 88%, Yb: 10% and Er: 2%). The detailed investigation on the crystal structure using XRD and FESEM studies elucidate that even the 1 mol% addition of Cr3+ ions lead to the phase of the crystal from mixed to hexagonal while retaining the shape of the crystals as hexagonal microprism. The FTIR and diffuse reflectance studies further confirms the presence of Cr3+ ions in the host lattice. The luminescence studies carried out confirm that the green as well as red emission of the samples is affected greatly with the Cr3+ ion concentration with an optimum concentration of 5 mol % and further addition leads to substantial quenching in the luminescence. The laser power dependent studies unambiguously show that the transitions 2H11/2 → 4I15/2 (G1), 4S3/2 → 4I15/2 (G2) and 4F9/2 → 4I15/2 (R) transitions are multi-photon process. The temperature dependent studies in the physiologically relevant region (30–60 °C) of the thermodynamically coupled states of G1 and G2 follows a linear behavior and can be explored as optical thermometer. The results provided here are relevant for the potential practical applications in bioimaging, thermometry and luminescent devices.