Variable photoluminescence and magnetic behaviors of Mn-Ho-codoped silicate glasses synthesized by sol-gel processing

Sol-gel processing has been employed for synthesis of single Mn-, Ho-doped and Mn-Ho-codoped silicate glasses. These glasses were characterized using optical absorption, photoluminescence (PL) emission and excitation spectroscopy. Ho3+ activator resulted in several optical absorption bands in the ultraviolet, visible and near infrared spectral regions. PL results revealed that various emissions covering the whole range of visible region, i.e. ranging from the blue to the red spectral regions, could be efficiently recorded. These emissions have been remarkably varied by changing of the excitation wavelength, type of activator ions, their concentration and their codoping effect. CIE chromaticity diagram and the corresponding (x, y) coordinates were utilized to detect definitely the overall color of multi-chromatic spectral emissions obtained in each spectrum. Vibrating sample magnetometry (VSM) was used to investigate the magnetic behavior of the phosphors. VSM data indicated that the single Mn-doped silica glass exhibited ferromagnetic behavior with relatively low magnetization. Whilst, all the other single Ho-doped and Mn-Ho-codoped silica glasses exhibited linear paramagnetic behavior whose magnetization values significantly increased with increasing of the Ho-concentration and its codoping with the Mn2+ ions. This superparamagnetism was endowed to these glasses by the remarkable spin of Ho3+ dopant that overcame the ferromagnetism of Mn2+ ions. The present sol-gel glassy phosphors can serve as potential LEDs in various applications.