Mn2+/Mg2+ co-doped AlON ceramic with ultra-narrowband green emission combining high transparency toward a wide gamut backlight application.

Narrowband green-emission, combined with superior physicochemical stability and thermal performance, is regarded as a common pursuit in backlight display applications. However, mainstream phosphor-converted materials composed of resin or silicone resin easily encounter the dilemma of thermal decomposition and chemical corrosion for practical use. To overcome this problem, in this work, Mn2+/Mg2+ co-doped AlON ceramic is successfully realized with ultra-narrowband green-emission and high transparency. The luminescent property of AlON: Mn2+-Mg2+ ceramic exhibits narrowband green emission centered at 509 nm with a full width at half maximum of 36 nm, which is smaller than the corresponding powder counterpart (44 nm). Moreover, AlON: Mn2+-Mg2+ ceramic presents a wide color gamut (103.6%) and high color purity (74%). Concurrently, high transmittance of this ceramic, at 82%, unveils a potential innovation in the display technology field. This work may facilitate the development of narrowband green light-emitting converters based on AlON: Mn2+-Mg2+ transparent ceramics in large color gamut backlight display applications.

Ultrapure single-band red upconversion luminescence in Er3+ doped sensitizer-rich ytterbium oxide transparent ceramics for solid-state lighting and temperature sensing.

Achieving single-band upconversion (UC) is a challenging but rewarding approach to attain optimal performance in diverse applications. In this paper, we successfully achieved single-band red UC luminescence in Yb2O3: Er transparent ceramics (TCs) through the utilization of a sensitizer-rich design. The Yb2O3 host, which has a maximum host lattice occupancy by Yb3+ sensitizers, facilitates the utilization of excitation light and enhances energy transfer to activators, resulting in improved UC luminescence. Specifically, by shortening the ionic spacing between sensitizer and activator, the energy back transfer and the cross-relaxation process are promoted, resulting in weakening of green energy level 4S3/2 and 2H11/2 emission and enhancement of red energy level 4F9/2 emission. The prepared Yb2O3: Er TCs exhibited superior optical properties with in-line transmittance over 80% at 600 nm. Notably, in the 980nm-excited UC spectrum, green emission does not appear, thus Yb2O3: Er TCs exhibit ultra-pure single band red emission, with CIE coordinates of (0.72, 0.28) and color purity exceeding 99.9%. To the best of our knowledge, this is the first demonstration of pure red UC luminescence in TCs. Furthermore, the luminescent intensity ratio (LIR) technique was utilized to apply this pure red-emitting TCs for temperature sensing. The absolute sensitivity of Yb2O3: Er TCs was calculated to be 0.319% K-1 at 304 K, which is the highest level of optical thermometry based on 4F9/2 levels splitting of Er3+ known so far. The integration between pure red UC luminescence and temperature sensing performance opens up new possibilities for the development of multi-functional smart windows.

Developing Smart Temperature Sensing Window Based on Highly Transparent Rare-Earth Doped Yttrium Zirconate Ceramics.

Lanthanide-ion-based thermometers have been widely researched and utilized as contactless temperature sensing materials. Cooperating with the unique optical and excellent physical properties of transparent ceramics, Er3+/Yb3+ co-doped Y2Zr2O7 transparent ceramics were successfully fabricated as temperature sensing window materials. Homogeneous distribution of elements inside samples together with high transmittance (nearly 73%) makes it possible as an observing window. Upon excitation at 980 nm, room-temperature luminescent performance was systemically researched for explaining the energy transfer mechanism between Yb3+ and Er3+ ions. The FIR method was introduced for thermally coupled energy levels to realize temperature sensing ability. Detecting sensitivity at different temperatures was also calculated (1.24% K-1 at 303 K), suggesting that Yb3+, Er3+:Y2Zr2O7 are adequate for high sensitivity temperature detecting application. It is also investigated that the concentration of Yb3+ ions not only affects the emission color at room-temperature but also has influence on the sensitivity of temperature and 10 mol % Yb3+, 2 mol % Er3+:Y2Zr2O7 was found to be the most sensitive one. A demonstration experiment was also carried out to validate its application as a smart temperature sensing window. These results suggested that Yb3+, Er3+:Y2Zr2O7 transparent ceramics can have potential for temperature monitoring applications, especially as novel window materials under extreme circumstances.

Defect Regulation of Terbium-Doped Y2Zr2O7 Transparent Ceramic for Wide-Range Multimode Tunable Light-Shielding Windows.

In the most promising new window materials, the light-blocking property of the state-of-the-art transparent polycrystalline ceramics is still located in the UV range, which undoubtedly limits their applications. Herein, a transparent Y2Zr2O7:Tb (YZO:Tb) ceramic for light-shielding windows was prepared by a solid-state reaction and vacuum sintering method. Two simple and efficient routes, with doping concentrations varying and air-annealing temperatures regulating, were developed for the first time to control the content of defect clusters [TbY4+-O2--TbY4+] and [TbY4+-e•], enabling the optical cutoff waveband of these ceramics spanning from UV and BV to green light. These defect clusters generated from an air-annealing process were proposed for the relevant reaction mechanisms concerning light erasure behavior. The controllably tailoring of optical cutoff wavelength from Tb single-doped YZO ceramics, adjusted by defect clusters, may open a novel door to develop lanthanide-doped transparent ceramics for wide-range tunable light-shielding windows.

Temperature-Independent Lifetime and Thermometer Operated in a Biological Window of Upconverting NaErF4 Nanocrystals.

Lifetime of lanthanide luminescence basically decreases with increasing the ambient temperature. In this work, we developed NaErF4 core-shell nanocrystals with compensation of the lifetime variation with temperature. Upconversion lifetime of various emissions remains substantially unchanged as increasing the ambient temperature, upon 980/1530 nm excitation. The concentrated dopants, leading to extremely strong interactions between them, are responsible for the unique temperature-independent lifetime. Besides, upconversion mechanisms of NaErF4 core-only and core-shell nanocrystals under 980 and 1530 nm excitations were comparatively investigated. On the basis of luminescent ratiometric method, we demonstrated the optical thermometry using non-thermally coupled 4F9/2 and 4I9/2 emissions upon 1530 nm excitation, favoring the temperature monitoring in vivo due to both excitation and emissions fall in the biological window. The formed NaErF4 core-shell nanocrystals with ultra-small particle size, highly efficient upconversion luminescence, unique temperature-independent lifetimes, and thermometry operated in a biological window, are versatile in applications such as anti-counterfeiting, time-domain manipulation, and biological thermal probes.

Efficient green upconversion luminescence in highly crystallized ultratransparent nano-glass ceramics containing isotropic KY3F10 nanocrystals.

Yb3+/Er3+ co-doped nano-glass ceramics (GCs) containing isotropic KY3F10 nanocrystals (NCs) are obtained from a simple ternary oxyfluoride glass by controlled crystallization. The nano-GCs thus obtained, albeit having very large crystallinity of ∼35%, are ultratransparent in the whole visible-light wavelength region of 300-700 nm. Remarkably enhanced green upconversion luminescence (UCL) of Er3+ (by 55 times) is observed in the nano-GCs as compared to the precursor glass. Absolute quantum efficiency of the green UCL reaches as high as 0.41±0.02% in the GCs under 10 W/cm2 power density. The UCL efficiency is comparable to that of the famous ZBLAN: Yb3+/Er3+ glass and GCs containing ß-NaYF4:Yb3+/Er3+ NCs, and nearly twice as large as that of GCs containing KYF4:Yb3+/Er3+ NCs under the same excitation conditions.

Upconversion enhancement through a facile, ultrafast, and low-threshold laser annealing strategy.

Particle size significantly affects the brightness of luminescent nanocrystals. Herein we firstly adopt a 1530 nm CW laser as the optical heating source to increase the particle size of Er3+ heavily doped nanocrystals, leading to giant enhancement of the luminescent intensity. The advantages of this method are mainly feature along the facile route, with an ultrafast process, and low threshold of the laser power density. The detailed mechanisms of the laser annealing are carefully investigated. In addition, fluorescence intensity ratio behaviours using different emission bands are comparatively investigated.

Ultrabright single-band red upconversion luminescence in highly transparent fluorosilicate glass ceramics containing KMnF3 perovskite nanocrystals.

With a specially designed composition, highly transparent Yb3+/Er3+-doped fluorosilicate glass ceramic (GC) containing KMnF3 perovskite nanocrystals (NCs) is obtained for the first time. The rare-earth ions are preferentially accumulated in regions embedded with KMnF3 NCs; as a result, a remarkably enhanced (by an order of magnitude) single-band red upconversion luminescence (UCL) is achieved. Absolute quantum efficiency of the red UCL, which cannot be measured in previous GCs owing to insufficiency, reaches as high as 0.10%±0.02% in the GC sample reported in this Letter. This value is even higher than that of the well-known multiband emitting ß-NaYF4:Er3+/Yb3+ NCs and widely recognized GCs containing NaYF4:Yb3+/Er3+NCs.

Efficient nanoheater operated in a biological window for photo-hyperthermia therapy.

Remotely monitoring and regulating temperature in a small area are of vital importance for hyperthermia therapy. Herein, we report ~11 nm NaErF4 nanocrystal as the ultra-small nanoheater, which is highly safe for biological applications. Under 1530 nm photon excitation, upconversion intensity of NaErF4 is significantly enhanced as compared to the conventionally used 980 nm pumping source. Upconversion mechanisms are discussed on the basis of power dependence measurements. Importantly, light-to-heat transformation efficiency of NaErF4 through 1530 nm pumping is determined as high as 75%. Efficient NIR emission, centered at ~800 nm and thus within the biological window, is used for the temperature feedback. The potential applications of this highly efficient nanoheater for controlled photo-hyperthermia treatments are also demonstrated.

Highly efficient upconversion luminescence of Er heavily doped nanocrystals through 1530 nm excitation.

Improving luminescence efficiency is of vital importance for applications of rare-earth-doped upconversion materials. Herein, we present highly efficient upconversion nanocrystal, which is brighter than the state-of-the-art Er3+/Yb3+ co-doped core-shell material, through Er3+ heavily doping and 1530 nm excitation. Moreover, upconversion characteristics and mechanisms of Er3+ heavily doped core nanocrystals and their core-shell counterparts are investigated carefully.

Concentration dependent optical transition probabilities in ultra-small upconversion nanocrystals.

Transition probability is of vital importance for luminescence process, whereas the effects of doping concentration have not been explored in the Er3+:NaGdF4. In this work, we investigate the radiative transition probabilities of Er3+ highly doped NaGdF4 sub 10 nm nanocrystals using J-O theory. It is found that the transition probabilities vary with changing Er3+ concentration, especially altering the ratio of Er3+ 2H11/2 to 4S3/2 level, which is highly useful for optical thermometers as they are thermally coupled. To validate the concentration dependent transition probabilities, significant enhancements of upconversion luminescence are achieved by epitaxial growth of the inert shell, and thermal sensing behaviors are investigated using the improved samples.