Nanosegregation and Neighbor‐Cation Control of Photoluminescence in Carbidonitridosilicate Phosphors

Abstract

Phosphor materials play a key role in white-light emitting diode (LED) devices based on gallium indium nitride (GaInN). [1][2][3][4][5] Phosphors for white LEDs should have good thermal stability and conversion efficiency and an excitation wavelength range in the UV to blue region (370-460 nm). [3,[6][7][8] The yellow-emitting phosphor (Y,Gd) 3 (Al,Ga) 5 O 12 :Ce 3+ is a well-known commercial example, but the lack of red emission results in cold white light and a low color-rendering index (CRI). [1,7,9,10] Nitride-based materials are more covalent than oxides, which improves thermal stability, and their greater crystal field splitting increases the red emission leading to warmer white light. [1,2,11,12] The chemistry of doped nitride phosphors is often complex and it may be difficult to understand how substitutions tune photoluminescence properties, as the local environment of activator ions may be quite different to the structural average. For example, local O/N ordering driven by the size mismatch between the Eu 2+ activator and the host cations was found to be an important effect in M 1.95 Eu 0.05 Si 5Àx Al x O 8Àx N x (M = Ca, Sr, Ba) phosphors. [12] Herein we demonstrate a new approach to controlling phosphor properties through segregation of activator cations on the nanoscale, as applied to Sr 1Àx Y 0.98+x Ce 0.02 Si 4 N 7Àx C x carbidonitridosilicate phosphors, and we show that overall trends evidence a significant neighboring-cation influence.Two structure types are encountered in the studied system. The SrYSi 4 N 7 (1147) type structure with hexagonal (space group P6 3 mc) symmetry contains a network of cornerlinked N(SiN 3 ) 4 structural units. [13][14][15][16] Sr and Y sites are coordinated by 12 and 6 nitrides, respectively. The related

Chemistry-Inspired Adaptable Framework Structures

“…47 Figure 8b gives another example on emission spectra evolution of the Sr 1−x Y 0.98+x Ce 0.02 Si 4 N 7−x C x phosphors through segregation of activators on the nanoscale. 48 Herein, the structures types of the two end-members are different. SrYSi 4 N 7 -type structure contains a network of corner linked N(SiN 3 ) 4 structural units with hexagonal (space group P63mc) symmetry, while Y 2 Si 4 N 6 C-type structure has monoclinic P21/c symmetry with C substituted only at the 4-connected positions x phosphors show an obvious red-shift, so that tunable blue-yellow emission can be realized (Figure 8b).…”

Synthesis, Crystal Structure, and Luminescence Properties of Y4Si2O7N2: Eu2+ Oxynitride Phosphors

“…The density of states corresponding to 270 nm, changes because of the change in covalency bond and crystal parameters. Due to the above reason, the difference of excitation spectra appeared . The above result indicates that the Zr 4+ ions participate in the luminescence process and play a positive role in improving the luminescence intensity of the phosphor.…”

Rare Earth Based Anisotropic Nanomaterials: Synthesis, Assembly, and Applications

“…Ce 3+ , widely studied and used for phosphor activators, is featured by its broadband 4f → 5d transition [90]. For other RE 3+ activators, intra-configurational 4f → 4f transitions are the main intrinsic mechanism for their luminescence processes.…”