Simultaneous double emission of blue-cyan light from europium nanostructures in solid host

Abstract

A sample of potassium bromide, doped with divalent europium ions, was stored at 200ºC for approximately six months and exhibited two emission bands at room temperature: blue and cyan. These emissions are associated with two types of nanostructures (NS) that develop during annealing. The emission spectra localized were obtained in a scanning zone (SZ) of 46x162m2 from a selected sample (SS) with dimensions of 900x320m2 and 90m in thickness using an experimental light-scanning design implemented in our laboratory. This design enabled us to capture the images and the emission spectra simultaneously. The sample was scanned using a step-by-step method with steps of 92nm, utilizing a 375nm laser diode as the excitation source. Luminescence was collected through reflection with a 100X microscope objective, and the response was recorded with a spectrometer. While scanning the crystal, several changes in the position and intensity of the emission spectra were observed. These changes corresponded to the stable dihalide phase (SDP) and the metastable dihalide phase (MDP). The average emission peaks for each phase were found at 424.7nm and 469.2nm for SDP and MDP, respectively. In certain regions, the intensity of the cyan emission band was slightly more significant than that of the blue emission band. The concurrent observation of these two emission bands confirms the coexistence of both phases within the single crystal. The NS was observed using atomic force microscopy (AFM), the blue luminescence is probably related to nanostructures < 80nm in diameter and up to 1nm in height. In comparison, the cyan luminescence is associated with laminar-type nanostructures > 80nm in diameter and a maximum height of 2.5nm. Additionally, NS in the SDP was found in isolation in certain areas. The step-by-step light scanning method employed in this study was crucial for simultaneously observing the two emission bands in this material.