Photon upconversion nanomaterials.

Photon upconversion through the use of lanthanide-doped materials has been the focus of a growing body of research in the fields of materials chemistry and physics for more than 50 years. The attraction of this field has been the ability to generate photons at shorter wavelengths than the excitation wavelength after laser stimulation. Despite its potential utility for a number of applications, photon upconversion has been primarily investigated in bulk glasses or crystalline materials. That situation dramatically changed in the mid-2000s, with the widespread research in the development of upconversion nanomaterials. As a unique class of optical materials, upconversion nanomaterials exhibit useful applications spanning from lighting to volumetric 3D displays to photovoltaics. Particularly, nanosized upconversion nanocrystals have proven valuable as luminescent labels for chemical and biological sensing with marked improvements in the sensitivity and versatility of the sensors. Recent advances in the field of upconversion nanomaterials have motivated us to initiate a thematic issue focusing on fundamental principles, synthetic strategies, materials characterization, broad applications, and a Department of Chemistry, National University of Singapore, Singapore 117543, Singapore. E-mail: chmlx@nus.edu.sg b Institute of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 117602, Singapore c Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, PKU-HKU Joint Laboratory in Rare Earth Materials and Bioinorganic Chemistry, Peking University, Beijing 100871, China. E-mail: yan@pku.edu.cn d Department of Chemistry and Biochemistry and Centre for NanoScience Research, Concordia University, Montreal, Quebec, H4B 1R6, Canada. E-mail: john.capobianco@concordia.ca † Part of the photon upconversion nanomaterials themed issue.