Controlling Selective Doping and Energy Transfer between Transition Metal and Rare Earth Ions in Nanostructured Glassy Solids

Abstract

Selective doping of optically active ions into the nanocrystalline phase(s) of glass ceramics is of interest for photoluminescence (PL) applications to control the energy transfer (ET) processes between dopants on the nanometer length scale. Here, the focus is on explaining the essential knowledge of the distribution of two groups of active ions: transition metal (Ni2+ and Cr3+) and rare earth (Yb3+ and Er3+) ions, which are doped into i) single‐phase Ga2O3 and ii) dual‐phase Ga2O3 and YF3 nanocrystals (NCs). These NCs are obtained by thermally crystallizing ternary silicate‐ and quinary fluorosilicate‐based glasses, respectively. It is found that the two types of active ions can successfully be doped into Ga2O3 NCs, resulting in enhanced ET between the dopants because of the small separation distance of, e.g., <10 Å, whereas ET is significantly suppressed when Ga2O3 and YF3 NCs are coprecipitated. In this case, the studied rare earth ions have a high propensity for being selectively doped in YF3 NCs. The studied transition‐metal ions can always be found in Ga2O3 NCs irrespective of the presence of the fluoride phase. The selective doping and the ET between the two types of active ions can be controlled simultaneously on annealing. This may allow for the achievement of diverse PL properties, such as ultrabroadband near‐infrared and upconversion‐mediated Stokes emissions.

Correlation between ultrabroadband near‐infrared emission and Yb3+/Ni2+ dopants distribution in highly transparent germanate glass‐ceramics containing zinc gallogermanate nanospinels

“…The enrichment of Zn 2+ , Ga 3+ , Yb 3+ (Figure B), and Ni 2+ (Figure D) in the NCs is clearly seen, whereas the NCs are slightly poor in Ge 4+ . The result agrees with our recent observation that Yb 3+ prefers to partition in the nanospinels rather than accumulating at the interfaces between the NCs and the surrounding glass matrix …”

“…The bands centered at 428, 830, and 1686 nm in the PG are ascribed to the presence of the trigonal bipyramid fivefold and tetrahedral fourfold coordinated Ni 2+ . After crystallization, completely new absorption bands centered at 610, and 1050 nm are formed in the GC, which can be attributed to the spin‐allowed 3 A 2 (F)→ 3 T 1 (F) and 3 A 2 (F)→ 3 T 2 (F) transitions of Ni 2+ in octahedral sites, in agreement with previous reports . The result suggests that almost all the Ni 2+ ions are partitioned in the ZGGO NCs by substitution for the octahedrally coordinated Ga 3+ sites, for example.…”

“…The critical distance of interaction between Yb 3+ and Ni 2+ in the studied GC sample is R c ≈13.8 Å. This value is close to those found in GCs embedded with LiGa 5 O 8 (~15.3 Å) or γ‐Ga 2 O 3 (~14.3 Å) nanospinels . If Yb 3+ were residing in the glassy matrix, which would hint no ET between Yb 3+ and Ni 2+ when Yb 3+ is <0.1 mol.%.…”

“…TEM samples were prepared by a conventional mechanical polishing and ion beam milling technique (PIPS II system from GATAN). For a more detailed description of the TEM experiment, please refer to our recent publications …”

“…In fact, many previous studies were based on the assumption that RE ions stay in the glassy phase (GP) rather than partitioning in the thermally grown nanospinels. However, our recently studies provided clear evidence that RE ions accumulate preferentially in the embedded nanospinels (eg, γ‐Ga 2 O 3 ), and perhaps more interestingly the doping efficiency of RE ions in the nanospinels depends on the ionic radius of the RE ion dopants . The simultaneous partitioning of TM and RE ions in the embedded nanospinels imposes a strong influence on the ET processes occurring between the dopants, such that the PL functions can be tailored in demand …”