Materials Suitable for preparing Inorganic nanocasts of butterflies and other insects

Replication of 3D-structures, in particular those that have a periodic modulation of a dielectric material at optical wavelengths and below have proven very difficult to fabricate. The majority of such replication techniques are complex or use moisture sensitive precursors requiring the use of for example a glove box. Here we demonstrate how an air stable supersaturated europium-doped yttrium nitrate phosphor precursor solution has the ability to easily impregnate a structure or produce a cast yielding faithful replicas composed of Y2O:Eu3+ after a final short annealing step. New replicas of Lepidoptera (moth) wing scales using field emissionscanning electron microscopy, structures down to 10 nm have been imaged. Moreover as these replicas are made of phosphors, their luminescence in some cases may be modulated by the internal periodic modulation built into their structures. In this work we will discuss more recent results on the use of the phosphors for making nanocasts of moth wing scales and show a range of beautiful pictures to show what the method can achieve

Symmetry-related transitions in the spectrum of nanosized Cubic Y2O3: Tb3+

Herein the preparation and cathodoluminescence of nanoparticles of cubic Y2O3:Tb3+ having Tb3+ concentration varying between 0.1 and 10 Mol% are described. The cathodoluminescence spectra were recorded with a high resolution spectrometer, which enabled the identification of Tb3+ lines with C2 and S6 symmetry: the lines at 542.8 nm and 544.4 nm were designated as 5D4→7F5 (C2) and 5D4→7F5 (S6) respectively. The critical distance for energy transfer from Tb3+ ions at S6 lattice sites to Tb3+ ions at C2 lattice sites was found to be >1.7 nm. At the greater distances which prevail at low Tb3+ concentration, this energy transfer virtually stops. From cathodoluminescence spectra recorded in a scanning transmission electron microscope it was concluded that this energy transfer also did not take place if the temperature was reduced below 102 K. The efficiency of the cathodoluminescence of 1% Y2O3:Tb3+ was 6 lm/w at a beam voltage of 15 kV. The decay time of the 5D4→7F5 (C2) transition was substantially shorter than that of the 5D4→7F5 (S6) transition at low Tb3+ concentrations. The decay behavior of the cathodoluminescence images in a field emission scanning electron microscope has been explained in terms of phosphor saturation.We are grateful to the EPSRC and the Technology Strategy Board (TSB) for funding the PURPOSE (TP11/MFE/6/I/AA129F; EPSRCTS/G000271/1) and CONVERTED (JeS no. TS/1003053/1) programs. We are also grateful to the TSB for funding the CONVERT program

Symmetry-related transitions in the photoluminescence and cathodoluminescence spectra of nanosized cubic Y2O3:Tb3+

Herein the photoluminescence spectra of nanosized cubic Y2O3:Tb3+ having Tb3+ concentrations varying between 0.1 and 10 Mol% are described. Low temperature cathodoluminescence spectra from these materials recorded in a scanning transmission electron microscope are presented and discussed. By studying the photoluminescence-spectra recorded at room temperature and focused on the 5D4→7F5 (C2) and 5D4→7F5 (C3i) transitions, at 542.8 and 544.4 nm respectively, it was found that the critical distance for energy transfer from Tb3+ ions at C3i lattice sites to Tb3+ ions at C2 lattice sites was 1.7 nm; at distances >1.7 nm, which prevail at low Tb3+ concentration, this energy transfer virtually stops. The gradual change of the excitation spectra upon increasing the Tb3+ concentration is also explained in terms of energy transfer from Tb3+ at C3i sites to Tb3+ at C2 sites. Cathodoluminescence spectra recorded at low temperatures with the scanning transmission electron microscope provided additional evidence for this radiationless energy transfer.We are grateful to the EPSRC and the Technology Strategy Board (TSB) for funding the PURPOSE (TP11/MFE/6/I/AA129F; EPSRCTS/G000271/1) and CONVERTED (JeS no. TS/1003053/1) programs. The TSB funded the CONVERT program

Investigating the emission characteristics of single crystal YAG when activated by high power laser beams

© The Author(s) 2016. Limitations associated with light emitting diodes (LEDs) operating under high current densities due to the efficiency droop has created a need to look for alternative light sources; here we report investigations on the potential of laser diodes (LDs) for high brightness lighting solutions. High power laser diodes require phosphor targets with certain performance criteria such as high thermal conductivity, efficiency and structural geometry. Here we examine the possibility of using single crystal YAG:Ce phosphor materials as potential targets for generation of light via laser diodes. We report on the emission properties of the crystals with different sizes and examine the effect of laser beam incident angle incident on crystal target emission

Laser-Activated Luminescence of BaAl2O4:Eu

© 2020 The Author(s). In this article the laser-activated (LA) luminescence of BaAl2O4 doped with 3 mol% Eu2+ and SrAl2O4 doped with 700 ppm Eu2+ is described. The LA spectrum of BaAl2O4:Eu did not show any emission from Eu2+, but rather luminescence from the Eu3+ ion. This surprising result is explained in terms of ionization of the excited Eu2+ ions (photo-ionization), while the freed electrons are trapped in an excited state of the F-centre: this is considered to be a deep trap. The temperature of the ferroelectric-paraelectric phase transition in BaAl2O4 has been determined at ≈180 °C from the Raman spectra recorded at various temperatures.PURPOSE (TP11/MFE/6/1/AA129F; EPSRC TS/G000271/1) and CONVERTED (JeS no. TS/1003053/1), PRISM (EP/N508974/1) and FAB3D programs

Ultraviolet and blue cathodoluminescence from cubic Y2O3 and Y2O3: Eu3+ generated in a transmission electron microscope

Herein we describe the investigation of transmission electron microscopeof non-doped Y2O3 and Y2O3 doped with Eu3+ in a transmission electron microscope (TEM) equipped with a spectrometer to detect cathodoluminescence from individual particles. Each submicron particle was made up of nanometre sized crystals. We found that these crystals showed a broad emission band at 353 nm upon bombardment with 200 keV or 80 keV electrons. Upon increasing the Eu3+ concentration from 0 to 2 mol% this UV/blue emission was gradually quenched: at Eu3+ concentrations >2 mol% no UV/blue emission was detected, only the well-known cathodoluminescence (CL) spectrum of Y2O3:Eu3+ could be recorded. This UV/blue emission has been attributed to the intrinsic luminescence of Y2O3 caused by self-trapped excitons. We found that the UV/blue luminescence was strongly temperature dependent and that the trap depth of the self-trapped excitons was 0.14 eV. The ratios of the spectral radiances of 5D1 → 7FJ and 5D0 → 7FJ (J = 0, 1...6) Eu3+ transitions in the CL-TEM spectra of Y2O3:Eu3+ at low Eu3+ concentrations was about a factor of 10 larger than those recorded at 15 keV. This phenomenon has been explained by absorption of the intrinsic luminescence of Y2O3 by Eu3+.The EPSRC and the Technology Strategy Board (TSB) funded the PURPOSE (TP11/MFE/6/I/AA129F; EPSRC TS/G000271/1), CONVERTED (JeS no. TS/1003053/1) and PRISM (EP/N508974/1) programs. The TSB for funding the CONVERT program.We are grateful to the EPSRC and the Technology Strategy Board (TSB) for funding the PURPOSE (TP11/MFE/6/I/AA129F; EPSRC TS/G000271/1), CONVERTED (JeS no. TS/1003053/1) and PRISM (EP/N508974/1) programs. We are also grateful to the TSB for funding the CONVERT program

New Developments in Cathodoluminescence Spectroscopy for the Study of Luminescent Materials

© 2017 by the authors. Herein, we describe three advanced techniques for cathodoluminescence (CL) spectroscopy that have recently been developed in our laboratories. The first is a new method to accurately determine the CL-efficiency of thin layers of phosphor powders. When a wide band phosphor with a band gap (Eg > 5 eV) is bombarded with electrons, charging of the phosphor particles will occur, which eventually leads to erroneous results in the determination of the luminous efficacy. To overcome this problem of charging, a comparison method has been developed, which enables accurate measurement of the current density of the electron beam. The study of CL from phosphor specimens in a scanning electron microscope (SEM) is the second subject to be treated. A detailed description of a measuring method to determine the overall decay time of single phosphor crystals in a SEM without beam blanking is presented. The third technique is based on the unique combination of microscopy and spectrometry in the transmission electron microscope (TEM) of Brunel University London (UK). This combination enables the recording of CL-spectra of nanometre-sized specimens and determining spatial variations in CL emission across individual particles by superimposing the scanning TEM and CL-images.We are grateful to the EPSRC and Technology Strategy Board (TSB) for funding the PURPOSE (TP11/MFE/6/1/AA129F; EP-SRC TS/G000271/1) and CONVERTED (JeS No. TS/1003053/1), PRISM (EP/N508974/1) and FAB3D programs. We are finally grateful to the TSB for funding the CONVERT program

Structure and luminescence analyses of simultaneously synthesised (Lu1-xGdx)2O2S:Tb(3+) and (Lu1-xGdx)2O3:Tb(3+)

Herein we describe the synthesis and luminescence of nanosized (Lu1−y–xGdx)2O2S:Tby and (Lu1−y–xGdx)2O3:Tby phosphors with y = 0.1 mol% Tb3+ and y = 2 mol% Tb3+ and x ranging between 0 and 1. The concentration of Gd3+ (x) was varied in steps of 0.1 (molar ratio Gd3+). The samples at 0.1 < x < 0.7 contained a mixture of (Lu1−xGdx)2O3:Tb3+ and (Lu1−xGdx)2O2S:Tb3+, while the samples at x = 0 contained only Lu2O3:Tb3+. At 0.1 < x < 0.7 Lu2O2S:Tb3+ and Gd2O2S:Tb3+ did not form a solid solution, but rather crystallised into two slightly different hexagonal structures. This behaviour has been explained in terms of segregation of Lu and Gd between the oxide and oxysulfide phases: the oxide phase is more Lu-rich whereas the second oxysulfide phase is more Gd-rich. The photoluminescence spectra of the phosphors with 0.1 mol% Tb3+ showed a modest colour change of the fluorescence light from cyan to green when x was increased from 0 to 1, whereas the samples of the series with 2 mol% Tb3+ yielded essentially green light. From this analysis it was concluded that the colour change of (Lu1−xGdx)2O2S:0.1%Tb3+ is caused by increasing energy transfer of the 5D3-level of Tb3+ to the charge transfer band of (Lu1−xGdx)2O2S:Tb3+ upon increasing x. Since the samples with 100% Lu consisted of pure cubic Lu2O3:Tb3+, we had the opportunity to also study the symmetry-related PL of this compound. From this study we concluded that the C2–C3i doublet of the Tb3+ 5D4 → 7F5 transition behaves in the same way as the corresponding doublet in cubic Y2O3:Tb3+.We are grateful to the EPSRC and Technology Strategy Board (TSB) for funding the PURPOSE (TP11/MFE/6/1/AA129F; EP-SRC TS/G000271/1) and CONVERTED (JeS no. TS/1003053/ 1), PRISM (EP/N508974/1) and FAB3D programs. We are finally grateful to the TSB for funding the CONVERT program