Natural hybrid-mediated long-lived room temperature phosphorescence of milk powder

Abstract

Natural luminogens with long-lived room temperature phosphorescence (RTP) are charming and useful since the artificial one always requires complicated synthesis and lacks sustainability. Herein, milk powder (MP) has been found to emit striking afterglow with the duration and lifetime exceeding 10 s and 2 s under ambient conditions, respectively, not inferior to most advanced artificial organic phosphors. There are mainly three emission species in MP, one comes from aromatic amino acid residues, one comes from the combination of oxidation products, Maillard products, nicotinamide adenine dinucleotide (NADH) coenzyme, and clusteroluminescence of nonaromatic amino acid residues, and one comes from riboflavin and/or flavin adenine dinucleotide (FADH), leading to three distinguishable emission bands. Mechanistic studies indicate that the natural hybrid of milk minerals and various emission species, which can provide a rigid environment to suppress the excited-state molecular motion and enhance triplet exciton radiative transition, is responsible for the long-lived RTP. Consequently, MP with unique visible RTP properties is utilized as a versatile platform for green screen printing and information security. This interesting work will shed new light on natural long-lived RTP materials and inspire the design of other high performance RTP materials.