Ultrasensitive Pressure-Induced Optical Materials: Europium-Doped Hafnium Silicates with a Khibinskite Structure for Optical Pressure Sensors and WLEDs

Abstract

Ultrasensitive pressure-induced optical materials are of great importance owing to their potential applications in optical pressure sensors. However, the lack of outstanding pressure sensitivity, observable color evolution, and structure reliability limits their further development in both practical applications and luminescence theory. To overcome the above problems, an enlightening methodology is proposed to explore the high sensitivity and phase stability of hafnium silicate K2HfSi2O7 (KHSO) phosphor with a Khibinskite structure. By employing X-ray diffraction (XRD) Rietveld refinement, cryogenic spectroscopy, and ancillary calculations, information on Eu2+ ion occupation is completely obtained at atmospheric pressure. The remarkable pressure sensitivity (dλ/dP = 3.25 nm/GPa–1) and excellent phase stability up to 20 GPa, along with the reproducible color hue variation, exhibit unprecedented superiority when used in optical pressure sensors. These advantages can be assigned to the pressure-induced Eu2+-selective occupation and the unique properties of 5d–4f transition (Stokes shift, nephelauxetic effect, and intense crystal field strength), which are clearly proved by measuring the XRD patterns, Raman spectra, and Gaussian fitting spectra under compression and decompression processes. The excellent luminescence property manifests that KHSO/Eu2+ can be considered as a potential luminescent material for solid-state lighting and optical pressure sensors.

Defect-induced zero thermal quenching of a bright red-emitting nonlinear optical material

“…6(a). After exponential fitting and calculation, we found that these decay curves can be accurately fitted using a double exponential equation: 52–54 where I is for emission intensity, τ 1 and τ 2 are the decay times of the exponential components, and both A 1 and A 2 are constants. The average decay times for x in the range 5–25 are 2.09 ms, 2.55 ms, 2.66 ms, 2.67 ms, and 2.31 ms, respectively.…”

“…6(a). After exponential fitting and calculation, we found that these decay curves can be accurately fitted using a double exponential equation: [52][53][54]…”

Blue light‐excitable Eu‐doped yellow emitting borate KSr4B3O9 phosphor for white light‐emitting diodes

“…The similar profiles from ∼220 to 300 nm can be assigned to the host absorption, and the unique strong absorption band in the region of 360–500 nm only appear in KSBO: 1.25%Eu 2+ sample indicating the attribution to the 4f 7 →4f 6 5d transition of Eu 2+ 25 . To further identify the absorption edge, the Kubelka–Munk absorption coefficient ( K / S ) relationship is applied as follows 26 : $$\begin{equation}{\left[ {{\rm{ }}F{\rm{ }}\left( {{R}_\infty } \right){\rm{ }}hv{\rm{ }}} \right]}^n = {\rm{ }}A\left( {hv{\rm{ }} - {\rm{ }}{E}_g{\rm{ }}} \right)\end{equation}$$where A is the proportional constant, and ℎν stands for the photon energy. The ratio of absorption coefficient to reflection coefficient is determined as (𝑅 ∞ ).…”

“…The similar profiles from ∼220 to 300 nm can be assigned to the host absorption, and the unique strong absorption band in the region of 360-500 nm only appear in KSBO: 1.25%Eu 2+ sample indicating the attribution to the 4f 7 →4f 6 5d transition of Eu 2+ . 25 To further identify the absorption edge, the Kubelka-Munk absorption coefficient (K/S) relationship is applied as follows 26 :…”

Supersensitive Ratiometric Thermometry and Manometry Based on Dual‐Emitting Centers in Eu2+/Sm2+‐Doped Strontium Tetraborate Phosphors

“…Currently, to optically monitor pressure with luminescent materials, the spectroscopic parameters, such as the band position (line shift), the emission lifetime and the bandwidth are mainly used, as their values may change monotonously with pressure. [23,[30][31][32] Utilizing the band shift under high-pressure conditions, the sensitivity (dλ/dP) of commonly used ruby-based sensors (Al 2 O 3 :Cr 3+ ) is around 0.35 nm GPa −1 . [33,34] Yichao Wang et al reported the BaLi 2 Al 2 Si 2 N 6 :xEu 2+ phosphors for optical pressure sensing, exhibiting sensitivity of dλ/dP ≈ 1.58 nm GPa −1 .…”