Shuo Yuan

Ln3+-Sensitized Mn4+ near-infrared upconverting luminescence and dual-modal temperature sensing

In the past few decades, efficient photon upconversion (anti-Stokes) luminescence has been extensively studied and is almost exclusively restricted to lanthanide (Ln3+) doped fluorophores. However, investigations on upconversion emissions of transition metal activators, whose (Stokes) luminescence is known to be tunable via modifying the crystal-field of the hosts, are extremely scarce. In the present work, a strategy to achieve Mn4+-based room-temperature near-infrared upconversion luminescence with the aid of efficient energy transfer of Yb3+ → Ln3+ → Mn4+ in specially prepared Yb3+/Ln3+/Mn4+ (Ln = Er, Ho, Tm):YAlO3 products is reported for the first time. Steady-state and time-resolved upconversion emission spectra are adopted to systematically clarify the related energy transfer mechanisms and determine energy transfer efficiencies. Benefitting from the completely different thermal-quenching mechanisms of Mn4+ and Ln3+ as well as the intermediate crystal field environment of Mn4+ in the YAlO3 host, the possibility of using a Mn4+/Ln3+-based dual-emitting upconversion fluorescence intensity ratio and Mn4+ upconversion lifetime as dual-modal temperature signals for accurate temperature sensing is demonstrated. It is believed that this preliminary study will offer a significant advance in exploring novel transition metal-based upconversion materials as well as self-calibrated optical thermometric media.

Dual-phase phosphor-in-glass based on a Sn–P–F–O ultralow-melting glass for warm white light-emitting diodes

Herein, a novel alkaline metal fluoride-modified Sn–P–F–O ultralow-melting glass was designed to find a possible application of it as a host matrix for dispersing commercial phosphors. X-ray diffraction, differential scanning calorimetry, X-ray photoelectron spectroscopy, and Fourier transform infrared (FTIR) spectroscopy were adopted to study the related glass structure. Importantly, a dual-phase phosphor-in-glass (PiG) inorganic color converter was successfully prepared by directly co-sintering the mixture of Sn–P–F–O-based glass components, Ce3+:Y3Al5O12 yellow phosphors, and Eu2+:CaAlSiN3 red phosphors at a temperature as low as 350 °C; moreover, the yellow to red tunable luminescence was easily realized via modifying the content of the red phosphor in the glass matrix. As a consequence, warm white light-emitting devices with improved optical performances were easily achieved by combining the fabricated dual-phase PiG with an InGaN blue chip.

Eu3+-Doped glass ceramics containing NaTbF4 nanocrystals: controllable glass crystallization, Tb3+-bridged energy transfer and tunable luminescence

Herein, hexagonal and cubic NaTbF4:Eu3+ nanocrystals embedded in transparent glass ceramics were successfully synthesized via a conventional melt-quenching technique followed by glass crystallization for the first time. Structural and spectroscopic characterizations evidenced the composition-dependent crystalline precipitation and the partition of Eu3+ dopants into the NaTbF4 host. In particular, the energy transfer mechanism from Tb3+ to Eu3+ was systematically investigated by photoluminescence spectra and decay curves, confirming that the energy transfer chain of Tb3+ → (Tb3+)n → quenchers in NaTbF4 nanocrystals was replaced by Tb3+ → (Tb3+)n → Eu3+ with the incorporation of Eu3+. The discrepant luminescence behaviors in terms of on-phase transformation were also studied. Furthermore, tunable emission could be achieved by merely adjusting the content of Eu3+, producing distinguishable emissions. As a consequence, it could be expected that NaTbF4:Eu3+ nanocrystals embedded in glass ceramics are promising candidates for applications in lightings and displays.

Tunable Optical Properties and Enhanced Thermal Quenching of Non-Rare-Earth Double-Perovskite (Ba1–xSrx)2YSbO6:Mn4+ Red Phosphors Based on Composition Modulation

Non-rare-earth Mn4+-doped double-perovskite (Ba1- xSr x)2YSbO6:Mn4+ red-emitting phosphors with adjustable photoluminescence are fabricated via traditional high-temperature sintering reaction. The structural evolution, variation of Mn4+ local environment, luminescent properties, and thermal quenching are studied systematically. With elevation of Sr2+ substituting content, the major diffraction peak moves up to a higher angle gradually. Impressively, with increasing the substitution of Ba2+ with Sr2+ cation from 0 to 100%, the emission band shifts to short-wavelength in a systematic way resulting from the higher transition energy from excited states to ground states. Besides, this blue-shift appearance can be illuminated adequately using the crystal field strength. The thermal quenching of the obtained solid solution is dramatically affected by the composition, with the PL intensity increasing 16% at 423 K going from x = 0 to 1.0. The w-LEDs component constructed by coupling the UV-LED chip with red/green/blue phosphors demonstrate an excellent correlated color temperature (CCT) of 3404 K, as well as color rendering index (CRI) of 86.8.

CsPbX3 (X = Br, I) perovskite quantum dot embedded low-melting phosphosilicate glasses: controllable crystallization, thermal stability and tunable emissions

In this work, low-melting (700 °C) phosphosilicate glasses embedded with CsPbX3 (X = Br, I) perovskite quantum dots (QDs) were fabricated via a glass crystallization strategy. The as-prepared CsPbBr3 QDs@glass nanocomposites exhibited typical green luminescence assigned to exciton recombination radiation and outstanding thermal stability due to the protection of the robust inorganic glass host. Multi-color tunable emissions in the spectral range of 500–750 nm were achieved by modifying the molar ratio of halide sources in the glass. As a proof-of-concept experiment, a light-emitting diode device was constructed by coupling the green-emitting CsPbBr3 QDs@glass and red-emitting CsPbBr2I QDs@glass with a commercial InGaN blue chip, yielding a bright white light emission with excellent optoelectronic performance. It is expected that the investigated CsPbX3 QDs@glass nanocomposites may find promising application as color converters in solid-state-lighting.

In Situ Crystallization Synthesis of CsPbBr3 Perovskite Quantum Dot-Embedded Glasses with Improved Stability for Solid-State Lighting and Random Upconverted Lasing

All-inorganic cesium lead bromide CsPbBr3 perovskite quantum dots (QDs) are emerging as potential candidates for their applications in optoelectronic devices but they suffer from poor long-term stability due to their high sensitivity to UV irradiation, heat, and especially to moisture. Although great advances in improving stability of perovskite QDs have been achieved by surface modification or encapsulation in polymer and silica, they are not sufficiently refrained from external environment due to nondense structures of these protective layers. In this work, in situ nanocrystallization strategy is developed to directly grow CsPbBr3 QDs among a specially designed TeO2-based glass matrix. As a result, QD-embedded glass shows typical bright green emission assigned to exciton recombination radiation and significant improvement of photon/thermal stability and water resistance due to the effective protecting role of dense structural glass. Particularly, ∼90% of emission intensity is even remained after immersing QD-embedded glass in water up to 120 h, enabling them to find promising applications in white-light-emitting device with superior color stability and low-threshold random upconverted laser under ambient air condition.

Near-infrared to short-wavelength upconversion temperature sensing in transparent bulk glass ceramics containing hexagonal NaGdF_4: Yb^3+/Ho^3+ nanocrystals

Transparent glass ceramics containing hexagonal NaGdF4: Yb3+, Ho3+ nanocrystals were successfully fabricated via self-crystallization, which was further confirmed by XRD, TEM, HRTEM, and STEM-HADDF, as well as upconversion (UC) emission spectra. Impressively, GC750 exhibited fascinating upconversion luminescence, and the corresponding 5F1/5G6 and 5F2,3/3K8 states of Ho3+ were proven to be thermally coupled energy levels (TCELs), resulting in high temperature-sensitive behaviors based on fluorescence intensity ratio (FIR) for optical thermometry. As a consequence, a high relative sensitivity of 1.43%·K−1 at 390 K was achieved, offering a great potentially application in optical thermometry.