Photo/cathodoluminescence and stability of Gd₂O₂S:Tb,Pr green phosphor hexagons calcined from layered hydroxide sulfate

Abstract

Hydrothermal reaction at 150°C and pH = 10 for 24 hours crystallized (Gd,RE)2(OH)4SO4 layered hydroxide sulfate (monoclinic structure; RE = Pr, Tb), from which Gd2O2S:RE (hexagonal structure) green phosphor hexagons were derived via facile dehydration in flowing H2 at 1200°C. Rietveld refinement of the XRD patterns yielded cell dimensions that confirmed the direct crystallization of solid solution. Photoluminescence (PL) study at room temperature found absolute quantum yields of ~25.1% and 28.4%, CIE chromaticity coordinates of (0.145, 0.679) and (0.326, 0.566), and fluorescence lifetimes of ~2.36 μs and 1.21 ms for Pr3+ and Tb3+ under 300 and 275 nm UV excitations, respectively. Temperature‐dependent PL analysis (25‐200°C) indicated that both the Pr3+‐ and Tb3+‐doped phosphors have favorably good thermal stability and retained ~65% and 80% at 100°C and ~41% and 47% at 200°C of their initial emission intensities, respectively. The activation energy for the thermal quenching of PL was determined to be ~0.221 (Pr3+) and 0.314 eV (Tb3+). Cathodoluminescence (CL) found that both the phosphors exhibit increasingly higher emission intensity/brightness at a higher acceleration voltage (up to 7 kV) or beam current (up to 50 μA) and are stable under electron bombardment in the studied range. Raising beam current was suggested to be more effective to enhance CL.

A low temperature approach for photo/cathodoluminescent Gd2O2S:Tb (GOS:Tb) nanophosphors

“…The ln[( I 0 / I )‐1] vs 1/ kT plot is displayed as the bottom‐left inset in Figure B. Linear fitting of the data yielded a ΔE of ~0.305 eV, which is close to the value (~0.314 eV) reported for the ~10 μm sized (Gd 0.99 Tb 0.01 ) 2 O 2 S hexagons and is remarkably larger than the values of ~0.26 and 0.24 eV determined for the (Gd 0.925 Tb 0.075 ) 2 O 2 S phosphors synthesized via microwave‐assisted solid reaction and traditional high‐temperature solid reaction, respectively . The thermal quenching property of a phosphor is known to be affected by the crystallinity of the host lattice, concentration and spatial distribution of the activator, particle size and size distribution, and the type and content of impurity, which are all associated with the technique and parameters of powder processing.…”

“…The currently available strategies for LHS synthesis are limited to refluxing a mixed solution of RE sulfate and hexamethylenetetramine and hydrothermal reaction of RE nitrate with ammonium sulfate ((NH 4 ) 2 SO 4 ) . The products are, unfortunately, micron and even tens of micron sized platelike crystals, and/or aggregates of such crystals, from which RE 2 O 2 S of similar morphologies was resulted . It can thus be said that efficient synthesis of RE 2 O 2 S nanopowders of high chemical and phase purity is yet rather challenging.…”

Next generation lanthanide doped nanoscintillators and photon converters

“…The history and comparison of common inorganic scintillators is shown in Fig. 1 [11,[86][87][88][117][118][119][120][121][122][123].…”

Na(Gd,RE)(WO4)2 double tungstates (RE=Eu/Yb-Er): crystallization from a novel layered hydroxide precursor and favorable luminescence for optical thermometry

“…It is also noted in Figure 4b that the emission peaks basically showed same intensity loss rates with increasing temperature (Figure 4b), which indicated that the current DC phosphor cannot be employed as a probe for optical thermometry via fluorescence intensity ratio (FIR) mode. The activation energy (ΔE) of thermal quenching can be calculated from the Arrhenius Equation shown below [31,32]:…”