Photoluminescent spray-coated paper sheet: Write-in-the-dark

A simple formulation of an organic-inorganic composite for spray-coating was adopted toward photoluminescent paper sheets. The coating composite layer was composed of a synthetic organic adhesive binder mixed with an inorganic lanthanide-doped strontium aluminate pigment. Such pigment-binder formula was applied effectively onto paper sheets via spray-coating followed by thermal fixation. The applied transparent photoluminescent coated layer exhibited optimal excitation wavelength at 365 nm and emission band at 517 nm resulting in phosphorescence of the paper surface with a substantial development of green-yellow, bright white, turquoise, and off-white colors as indicated by CIE Lab color coordinates under ultraviolet irradiation. The mechanical, decay and lifetime properties of the composite photoluminescent coated layer were described. The standard techniques of morphological properties and elemental analysis were explored by scanning electron microscope (SEM), wavelength dispersive X-ray fluorescence (WDXRF), and energy dispersive X-ray spectroscopic analysis (EDX). The spray-coated paper sheets demonstrated good fastness to light and reversible phosphorescence without fatigue.