Metal halide perovskites are highly attractive for lighting applications, but the multiexcitonic emission processes in these crystals are largely unexplored. This study presents an investigation of Sb3+-doped Cs2ZrCl6 perovskite crystals that display double luminescence due to the intrinsic host self-trapped excitons (denoted as host STEs) and dopant-induced extrinsic self-trapped excitons (denoted as dopant STEs), respectively. Steady-state and transient-state spectroscopy reveal that the host and dopant STEs can be independently charged at specific energies. Density functional theory calculations confirm that the multiexcitonic emission stems from minimal interactions between the host and dopant STEs in the zero-dimensional crystal lattice. By selective excitation of different STEs through precise control of excitation wavelength, we further demonstrate dynamic color tuning in the Cs2ZrCl6:Sb3+ crystals. The color kinetic feature offers exciting opportunities for constructing multicolor light-emitting devices and encrypting multilevel optical codes.

Lanthanide-doped upconversion materials, capable of converting low-density (< 1000 W cm À2 ) near-infrared (NIR) excitation to ultraviolet (UV) and visible emissions, have generated a large amount of interests in the areas of information technology, biotechnology, energy, and photonics. [1] Significantly, recent developments in the synthetic and multicolor tuning methods have allowed easy access to upconversion nanoparticles with well-defined phase and size, core-shell structure, optical emission, and surface properties. [2][3][4][5] The technological advances provide promising applications in sensitive biodetection and advanced bioimaging without many of the constraints associated with conventional optical biolabels. [6] Despite the attractions, further progress in using upconversion processes has been largely hindered because upconversion nanoparticles are typically sensitized by Yb 3+ ions that only respond to narrowband NIR excitation centered at 980 nm. The absorption of 980 nm light by the water component in biological samples usually limits deep tissue imaging and induces potential thermal damages to cells and tissues. [7] Excitation of conventional upconversion nanoparticles at other wavelengths has been proposed to minimize the effect of water absorption. [8] But the use of this technique is limited mainly by the largely sacrificed excitation efficiency. Efforts have also been devoted to tuning the NIR response of photon upconversion through integration of various sensitizers such as metal ions (e.g.; Nd 3+ , V 3+ or Cr 5+ ) and organic dyes. [9] The progress has resulted in visible emission by NIR excitation in the 700-900 nm range where the transparency of biological samples is maximal. [9e-h] However, upconversion emission across a broad range of spectra in these systems have not been demonstrated largely owing to the uncontrollable nonradiative processes. Herein, we describe a novel design, based on nanostructural engineering to separate unwanted electronic transitions for constructing a new class of materials displaying tunable upconversion emissions spanning from UV to the visible spectral region by single wavelength excitation at 808 nm. We also show that these nanoparticles can surpass the constraints associated with conventional upconversion nanoparticles for biological studies.The nanostructure design for management of energy transitions is depicted in Figure 1. A core-shell-shell nanoparticle platform is used to host light-harvesting, upconverting, and optical tuning processes at separate layers through doping of appropriate lanthanide ions. Interlayer energy exchange interactions are mediated by arrays of lanthanide migrator ions that can bridge efficient energy transfer across the core-shell interface while filtering unwanted crossrelaxations. As a result, incompatible optical processes can be rationally combined to achieve flexible and efficient photon energy conversions.As a proof-of-concept experiment, we employed a NaYbF 4 @Na(Yb,Gd)F 4 @NaGdF 4 core-shell-shell nanoparticle host....

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Recoverable mechanoluminescence (ML), characterized by nondestructive and repetitive luminescence in response to a mechanical stress, has shown considerable promise in a variety of practical applications including lighting and display, as well as stress sensing and imaging. However, the progress in utilizing ML processes has been constrained by the difficulties in developing new ML materials and in ascertaining ML mechanism. In this paper, we report a new strategy to constructing recoverable ML materials by doping piezoelectric hosts with luminescent lanthanide ions, which simultaneously create luminescent centers and carrier traps in the host lattice. The viability of the strategy has been confirmed by assessing a series of Pr3+ activated calcium niobates composed of mCaO·Nb2O5 (m = 1, 2, and 3). Furthermore, systematical characterizations of the series of calcium niobates also reveal an unusual host dependent ML phenomenon. Our results are expected to expand the scope of designing ML materials and to deepen our understanding of ML mechanism, thereby promoting further utilization of recoverable ML.

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Rational control of photoluminescence against a change in temperature is important for fundamental research and technological applications. Herein, we report an anomalous temperature dependence of upconversion luminescence in Yb/Ho co-doped Sc 2 Mo 3 O 12 crystals. By leveraging negative thermal expansion of the crystal lattice, energy transfer between the lanthanide dopants is promoted as the temperature is increased from 303 to 573 K, resulting in an ∼5-fold enhancement of the emission. Meanwhile, the emission profile is also substantially altered due to the concurrent thermal quenching of selective energy states, corresponding to a clear shift in color from green to red. Via correlation of the red-togreen emission intensity ratio of Ho 3+ dopant ions with temperature, a ratiometric luminescence thermometer is constructed with a maximum sensitivity of 2.75% K −1 at 543 K. As the Sc 2 Mo 3 O 12 crystals are thermally stable and nonhygroscopic, our findings highlight a general approach for highly reversible control of upconversion by temperature in ambient air.

bottleneck and improve the system efficiency since the direct integration of ultrahigh memory layer on the processor chip is feasible. In another aspect, photonic memories are expected to speed up the von Neumann bottleneck and supercharge the performance of serial computers since the light signal can be regarded as the additional terminal of the underlying basic devices to ensure low power consumption. [7][8][9] The growing pursuit of practical photonic memories drives the rapid development of photonic technologies, especially in the region of nanofabricationcompatible optical signaling. In photonic memory, optical signals have to be converted into electrical signals and vice versa. However, it is difficult to make use of nearinfrared (NIR) light in photonic memory due to the inferior NIR sensitivity of most semiconductor materials originating from their broadband absorption. [10,11] In addition, although the decryption technology for visible light is mature in photonic memories, NIR photonic memristors are less progressed. [12][13][14] Upconversion materials are an anti-Stokes-shift type of photoluminescent compound that absorb several photons with long wavelength and emit one photon with shorter wavelength. [15,16] The upconversion nanoparticles (UCNPs) have been proposed as vital materials in various kinds of photonic applications including in vivo therapeutics, [17] biomedical imaging probes, [18] and optoelectronic [7,19] and optogenetic devices [20] due to their sharp emission bandwidth, high photochemical stability, and large anti-Stokes shift (up to several hundred nanometers). The UCNPs based on lanthanide ion (Yb 3+ , Er 3+ )-doped NaYF 4 have a narrow absorption band at 980 nm due to electronic transition between the energy levels in the lanthanide ion. [15] Thus, UCNPs exhibit extension of the applications in high-performance optoelectronics and multi-modal imaging in NIR band. However, the weak photo-absorption and insulating property of UCNPs limits their photon-electron conversion efficiency. The family of 2D materials including insulating hexagonal boron nitride (h-BN), semiconducting molybdenum disulfide (MoS 2 ) to semimetallic graphene and infrared-gapped black phosphorus has been demonstrated with distinct optical, electronic, and mechanical properties from conventional bulk materials. [21][22][23][24][25] Integration of UCNPs with 2D semiconducting materials results in heterostructures featuring increased sensitizing centers and energy transfer, which ensures the formation of more excitons and subsequently high sensitivity Photonic memories as an emerging optoelectronic technology have attracted tremendous attention in the past few years due to their great potential to overcome the von Neumann bottleneck and to improve the performance of serial computers. Nowadays, the decryption technology for visible light is mature in photonic memories. Nevertheless, near-infrared (NIR) photonic memristors are less progressed. Herein, an NIR photonic memristor based on MoS 2 -NaYF 4 :Yb 3+ , Er 3+ upconve...

Lanthanide-doped nanocrystals (NCs), which found applications in bioimaging and labeling, have recently demonstrated significant improvement in up-conversion efficiency. Here, we report the first up-conversion multicolor microcavity lasers by using NaYF4:Yb/Er@NaYF4 core-shell NCs as the gain medium. It is shown that the optical gain of the NCs, which arises from the 2- and 3-photon up-conversion processes, can be maximized via sequential pulses pumping. Amplified spontaneous emission is observed from a Fabry-Perot cavity containing the NCs dispersed in cyclohexane solution. By coating a drop of silica resin containing the NCs onto an optical fiber, a microcavity with a bottle-like geometry is fabricated. It is demonstrated that the microcavity supports lasing emission through the formation of whispering gallery modes.