Half a century after its initial emergence, lanthanide photonics is facing a profound remodeling induced by the upsurge of nanomaterials. Lanthanide-doped nanomaterials hold promise for bioapplications and photonic devices because they ally the unmatched advantages of lanthanide photophysical properties with those arising from large surface-to-volume ratios and quantum confinement that are typical of nanoobjects. Cutting-edge technologies and devices have recently arisen from this association and are in turn promoting nanophotonic materials as essential tools for a deeper understanding of biological mechanisms and related medical diagnosis and therapy, and as crucial building blocks for next-generation photonic devices. Here, the recent progress in the development of nanomaterials, nanotechnologies, and nanodevices for clinical uses and commercial exploitation is reviewed. The candidate nanomaterials with mature synthesis protocols and compelling optical uniqueness are surveyed. The specific fields that are directly driven by lanthanide doped nanomaterials are emphasized, spanning from in vivo imaging and theranostics, micro-/nanoscopic techniques, point-of-care medical testing, forensic fingerprints detection, to micro-LED devices.

Light-emitting diodes (LEDs) are widely used around the world. Scientists are attempting to develop LED devices that not only have high brightness but also have a high color rendering index (CRI). Phosphor materials play important roles in tuning and optimizing the final luminescent spectrum. Narrow-band emission phosphors must be incorporated into LED chips to achieve high CRI and efficacy. From this perspective, we introduce and discuss key points in the narrow-band emission spectrum. Three sets of phosphor examples, namely, Eu-doped (Ba,Sr)­Si2O2N2, UCr4C4-type structures, and β-SiAlON systems, are used to explain these points. First, we discuss the highly symmetrical local coordination environment of activators, which include cuboid and nine-coordinate structures. Second, we reveal the second-shell effect of the substituted cation channel. Third, we discuss the interaction between the electron from the activator and the vibration from the host lattice (electron–lattice interaction). These model systems help establish and design rules for narrow-band emission phosphors and may guide future studies in discovering potential phosphor candidates for practical applications.

Searching for narrow-band red-emitting and thermally stable phosphors is the ultimate strategy toward enhanced performance of phosphor converted light emitting diodes (pc-LED). The red emission is assured by the nitride host because of its relatively more covalent character than oxides and sulfides; however, the narrow emission is attributed to crystallographic, morphological, and electronic considerations. The symmetric coordination site ensures equal ligand effect in all direction fits well with the configuration of Eu 2+ f orbitals in the excited state, as observed in cuboid nitrides. Further, thermal stability is ascribed not only to suitable bandgap but more specifically, a relatively distant location of the lowest 5d level from the bottom of the conduction band (CB) that consequently entails high energy to quench excited electrons by exciting them further up to the CB. Modes toward the development of new nitride hosts with potentially narrow-band emission have been identified. A viewpoint on light-emitting diode (LED), backlighting, and laser lighting, which remains the most economically-rewarding phosphors application, is presented. Other exciting frontiers, such as agricultural illumination and persistent luminescence, maximize nitride systems that have other properties other than the stringent narrow-band red emission and excellent thermal stability required for the desired improvement of the mainstream LED application. is a Critical Review in Electrochemical and Solid State Science and Technology (CRES 3 T). This article was reviewed by Anant Setlur (setlur@ge.com) and Jing Wang (ceswj@mail.sysu.edu.cn). This paper is part of the JSS Focus Issue on Visible and Infrared Phosphor Research and Applications.The discovery, development, and commercialization of phosphors are expected to satisfactorily fare with the benchmark set for phosphor converted-LEDs. First, the excitation wavelength of the phoshpors must be compatible with the blue LED pump, thereby emitting the desired colors and consequently generating white light. Second, the quantum efficiency should be high. Third, phosphor must have a high absorption rate in the LED range, which technically narrows the choices to those that are excitable through 4f → 5d, d → d, np → nd, and ns → np transitions. Fourth, it must have high thermal quenching temperature. Fifth, the inherent stability against moisture and continuous irradiation ensures the durability and longevity of the device. Sixth, a rational design must be presented for the synthesis conditions from the selection of starting materials, synthesis strategy, and costs to allow the smooth cross-over to eventual industrial-scale production. 1,2Tuning the phosphor photoluminescence requires a tunable phosphor and a set of strategies to introduce changes in intensity, emission wavelength, and full width at half-maximum (fwhm). Moreover, the following are of paramount consideration in tuning the phosphor photoluminescence. First, a clear understanding of crystal and local structures and the investigati...

A Ce 3+ --doped nitrodoagnesoaluminate Sr[Mg 2 Al 2 N 4 ] phosphor was prepared from all--nitride precur-sors using gas pressure sintering method. The effective excitation by green light (510 nm) that revealed a broad emission from 550--650 nm prompted an innovation in the assembly of the pc--LED by using a blue chip LED that is sequentially coated with a green--emitting phosphor (β--SiAlON:Eu 2+ ) that excites the upper Sr[Mg 2 Al 2 N 4 ]:Ce 3+ layer thereby producing white light. The use of this broadband emitting phosphor and the innovative configu-ration generates white light and puts forward two promising innovations for pc--LEDs.Efficiency in the conversion of electrical energy to light has been a paramount consideration in the search and development of energy--saving alternatives to convention-al incandescent bulbs. 1 Phosphor--converted white light-emitting diodes (pc--WLEDs) have emerged as a promis-ing technology to revolutionize modern day lighting. This technology ensures energy--efficiency and improves color rendition and luminous efficacies. 1

A near infrared (NIR) persistent luminescent Ba[Mg2Al2N4]:Eu2+–Tm3+ phosphor chargeable by red light was prepared via a solid state reaction from all-nitride starting materials.

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The systematic substitution of Ba in the Sr site of Sr­[Mg2Al2N4]:Eu2+ generates a deep-red-emitting phosphor with enhanced thermal luminescence properties. Gas pressure sintering (GPS) of all-nitride starting materials in Molybdenum (Mo) crucibles yields pure-phase red-orange-colored phosphors. Peaks in the synchrotron X-ray diffraction (SXRD) data show a systematic shift toward smaller angles due to the introduction of the larger Ba cation in the same crystal structure. The photoluminescence property reveals that Ba substitution shifts the original emission wavelength of Sr­[Mg2Al2N4]:Eu2+ (625 nm) toward ∼690 nm for Ba­[Mg2Al2N4]:Eu2+. Thermal stability measurement of Sr1–x Ba x [Mg2Al2N4] indicates a systematic increase in stability from x = 0 to x = 1. X-ray absorption near-edge spectroscopy (XANES) results demonstrate the coexistence of Eu2+ and Eu3+. The red-shift and the enhanced thermal stability reveals that the distance of the emitting 5d level to the conduction band of Ba­[Mg2Al2N4]:Eu2+ is large. The ionic size mismatch of Eu occupying a Ba site reduces the symmetry, thereby further splitting the degenerate emitting 5d level and lowering the energy of the emitting center. The development of deep-red phosphors emitting at 670–690 nm (x = 0.8–1.0) offers possible candidates for plant lighting applications.

The Li–Si substitution in Sr[Mg2Al2N4]:Eu2+ enhanced thermal stability and tuned the emission further gaining insight into the energy transfer mechanism.