ABSTRACT
The phosphor with a highly condensed, rigid framework structure and a single crystallographic site often exhibit symmetrical narrow-band emission. It is challenging to achieve broadband emission by doping Eu2+ ions in similar structures. Here, we propose to control the occupation and quenching concentration of Eu2+ ions in a single-site matrix Sc2Si2O7 to increase efficiency and precise regulation of luminescence spectra substantially. The analysis of photoluminescence spectroscopy through steady-state, transient-state, and Gaussian fitting techniques has discovered two emission centers despite the presence of a single rare-earth substitution site. The theoretical calculations and bond valence sum subsequently prove that Eu2+ ions prefer substituting the Sc3+ and interval sites to emit intense cyan light. Under 340 nm excitation, broad cyan-emission (FWHM = 115 nm) is exhibited with a high quantum yield of 60.67 %. The present phosphor exhibits pronounced thermal stability, and the emission intensity can still keep 68.3 % at 170 °C compared to that at atmospheric temperature. The Sc2Si2O7: Eu2+ phosphor boasts exceptional potential as a highly efficient cyan component in full-spectrum WLEDs. By replacing the blue light component commonly found in WLEDs, the intelligent and healthy alternative Sc2Si2O7: Eu2+ phosphor can effectively decrease the harmful blue light. This work also highlights the critical need to analyze local phosphor distortions upon rare-earth substitution, especially in single crystallographic site structures.
ABSTRACT
Inhibiting energy migration between Eu3+ ions in a fixed host to get higher doping concentration is a permanent topic. Herein, a novel non-concentration quenching red-emitting K7SrY2-2xB15O30: xEu3+ (0.1 ≤ x ≤ 1.0) phosphor was synthesized via high-temperature sintering method. XRD measurement, Rietveld refinement results, and radius percentage deviation calculation demonstrated the phase purity and the occupation preference of Eu3+ ions. With continuously increasing doping Eu3+ ions, the absence of concentration quenching could be explained by long distance between two Eu3+ (7.012 Å) and the K7SrEu2B15O30 could exhibit striking photoluminescence performance with the highest emission wavelength centered at 617 nm. Meanwhile, under the radiation of 393 nm, the high internal quantum efficiency ( â¼ 78.71 %), excellent color purity ( â¼ 88.32 %) and robust thermal stability whose emission intensity at 140 °C could still reach â¼ 97.31 % could guarantee its potential application. When coating BaMgAl10O17: Eu2+, (Ba, Sr)2SiO4: Eu2+, and K7SrEu2B15O30 on a near-ultraviolet chip, the bright white light with a low correlated color temperature of 4211 K and CIE color coordinates of (0.3675, 0.3556) could be obtained. Taking the analytic results above, the non-concentration quenching K7SrY2B15O30: Eu3+ compound has great potential to act as a candidate for red-emitting phosphors in solid-state lighting field.
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.
ABSTRACT
The discovery of high color purity red-emitting phosphors is a major challenge for solid-state lighting materials. Benefitting from highly condensed and flexible framework structure of ß-Ca3(PO4)2-type compounds, we have successfully prepared three different kinds of novel high color purity red-emitting phosphors Sr19Mg2(PO4)14: Re3+ (Re3+= Eu3+, Sm3+, Pr3+) by using traditional sintering method. Rietveld refinement, SEM measurement, absorption spectra, emission/excitation spectra, fluorescence decay analysis and emission spectra in terms of different temperature were investigated and discussed clearly. The matrix optical band gap was calculated to be 4.5 eV by reflection data, which indicated the suitable host for rare earth doping. The single doped Eu3+, Sm3+ and Pr3+ phosphors could respectively exhibit characteristic and strong red emission peaks at 614 nm, 598 nm and 642 nm when excited by (near) ultraviolet radiation. Excitingly, all samples could obtain high color purity with the value of 91.6%, 90.6% and 84.8% for Eu3+, Sm3+, Pr3+ ions, respectively. Moreover, the thermal stability can stay strong which still keep over 75% at 150â when comparing with that at atmospheric temperature. The quantum efficiency (QE) is another important parameter for phosphors which were measured to be 46.6% for Eu3+, 53.1% for Sm3+ and 10.3% for Pr3+. The present work indicates that the Sr19Mg2(PO4)14: Re3+ phosphors are efficient red components with extraordinary color purity and high quantum efficiency for industrial applications as solid-state lighting materials.