Emerging and perspectives in microlasers based on rare-earth ions activated micro-/nanomaterials

Microlasers have drawn considerable attention for applications in future optoelectronic nanoscience and nanotechnology, owing to the capability of scaling physical dimension of devices down to micro-/nanometer level. Currently, the most popular optical gain micro-/nanomaterials for microlasers are inorganic semiconductors, organic dyes and polymers, and organic-inorganic hybrid perovskites. However, these optical gain micro-/nanomaterials are faced with severe issues of either complicated manufacturing process or low stability under air, thermal, and photo-irradiation ambient. Comparatively, rare-earth (RE) ions-activated micro-/nanomaterials show unique merits for building-up microlasers, including low-cost fabrication, high environmental stability, abundant spectrum bands (ultraviolet to mid-infrared), high photoluminescence quantum yield (PLQY), etc. Recently, new RE ions-activated luminescent materials have been exploited as low surface defects and high PLQY in terms of diverse micro-/nanostructures, which have stimulated great progress in emerging RE ions activated microlasers, in combination with design and fabrication of novel optical feedback micro-/nanoresonators. Herein, recent advances in RE ions activated microlasers are reviewed from the aspects of Materials and Theories (including optical gain media and feedback micro-/nanomaterials), as well as some enlightening works on Upconverting Pumped Microlasers and Down-Shifting/Converting Pumped Microlasers; finally, future Perspectives are given by providing inspiration for exploitation of RE ions activated micro-/nanolasers with desired performances.