Red phosphor materials play a key role in improving the lighting and backlit display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). However, the development of a red phosphor with simultaneous high efficiency, excellent thermal stability and high colour purity is still a challenge. In this work, unique non-concentration quenching in solid-solution Cs3Gd1 − xGe3O9:xEu3+ (CGGO:xEu3+) (x = 0.1–1.0) phosphors is successfully developed to achieve a highly efficient red-emitting Cs3EuGe3O9 (CEGO) phosphor. Under the optimal 464 nm blue light excitation, CEGO shows a strong red emission at 611 nm with a high colour purity of 95.07% and a high internal quantum efficiency of 94%. Impressively, this red-emitting CEGO phosphor exhibits a better thermal stability at higher temperatures (175–250 °C, >90%) than typical red K2SiF6:Mn4+ and Y2O3:Eu3+ phosphors, and has a remarkable volumetric negative thermal expansion (coefficient of thermal expansion, α = −5.06 × 10−5/°C, 25–250 °C). By employing this red CEGO phosphor, a fabricated pc-WLED emits warm white light with colour coordinates (0.364, 0.383), a high colour rendering index (CRI = 89.7), and a low colour coordinate temperature (CCT = 4508 K). These results indicate that this highly efficient red-emitting phosphor has great potential as a red component for pc-WLEDs, opening a new perspective for developing new phosphor materials.
Recently,
there has been growing interest in developing Bi3+-activated
luminescence materials for optoelectronic applications.
Herein, new yellow/orange-emitting ABZn2Ga2O7:Bi3+ (ABZGO, A = Ca, Sr; B = Ba, Sr) phosphors
with tunable optical properties are synthesized by an alkaline earth
cation substitution. When Sr2+ substitutes Ca2+ and Ba2+, the excitation wavelength has a red shift from
325 to 363 nm, matching well with the n-UV chip based white light-emitting
diodes (WLEDs). CaBaZn2Ga2O7:0.01Bi3+ (CBZGO:0.01Bi3+) exhibits two evident emission
peaks at 570 and 393 nm originating from the respective occupation
of Ca and Ba sites by Bi3+ ions. The optical tuning of
the CBZGO:Bi3+ phosphor is achieved by changing the Bi3+ doping content and excitation wavelength based on the selected
site occupation. Differently, both SrBaZn2Ga2O7:0.01Bi3+ (SBZGO:0.01Bi3+) and
Sr2Zn2Ga2O7:0.01Bi3+ (SZGO:0.01Bi3+) phosphors exhibit a single broad
emission band, peaking at 600 and 577 nm, respectively. Two different
Bi3+ sites are also verified respectively in SBZGO and
SZGO hosts by the Gaussian fitting of the asymmetric PL spectra and
lifetime analysis. The different luminescence behaviors of ABZGO:0.01Bi3+ phosphors should be ascribed to the synergistic effect of
the centroid shift, crystal-field splitting, and Stokes shift. Moreover,
the temperature-dependent PL spectra reveal that cation substitutions
of Sr2+ for Ca2+ and Ba2+ can efficiently
improve the thermal stability of ABZGO:0.01Bi3+ phosphors.
In view of different thermal responses to various temperatures for
two emission peaks of the CBZGO:0.01Bi3+ phosphor, an optical
thermometer is designed and has a good relative sensitivity (S
r = 1.453% K–1) at 298 K.
Finally, a WLED with CRI = 97.9 and CCT = 3932 K is obtained by combining
SZGO:0.01Bi3+ and BAM:Eu2+ phosphors with a
370 nm n-UV chip, demonstrating that SZGO:0.01Bi3+ is an
excellent yellow-orange-emitting phosphor for n-UV WLED devices. This
work stimulates the exploration of optical tuning by cation substitution
to obtain remarkable luminescence materials for optical temperature
sensing and WLED applications.
The development of lead‐free perovskite photoelectric materials has been an extensive focus in the recent years. Herein, a novel one‐dimensional (1D) lead‐free CsMnCl3(H2O)2 single crystal is reported with solvatochromic photoluminescence properties. Interestingly, after contact with N,N‐dimethylacetamide (DMAC) or N,N‐dimethylformamide (DMF), the crystal structure can transform from 1D CsMnCl3(H2O)2 to 0D Cs3MnCl5 and finally transform into 0D Cs2MnCl4(H2O)2. The solvent‐induced crystal‐to‐crystal phase transformations are accompanied by loss and regaining of water of crystallization, leading to the change of the coordination number of Mn2+. Correspondingly, the luminescence changes from red to bright green and finally back to red emission. By fabricating a test‐paper containing CsMnCl3(H2O)2, DMAC and DMF can be detected quickly with a response time of less than one minute. These results can expand potential applications for low‐dimensional lead‐free perovskites.
Near-infrared light-emitting
diodes (NIR-LEDs) are potential candidates in food composition analysis,
temperature and security monitoring, biometrics, and medical applications.
To realize the above objectives, the development of NIR-emitting phosphors
is urgently required. Herein, a novel NIR emission is successfully
achieved in Bi3+-activated XAl12O19 (X = Ba, Sr, Ca) compounds by constructing the selective site occupation
of Bi3+ in Al3+ polyhedra with small coordination
number. The designed phosphors exhibit broad-band NIR emission of
Bi3+ from 600 to 1000 nm. Interestingly, a broad photoluminescence
control from blue to red is also achieved by just changing the sintering
atmosphere. The blue emission of Bi3+ should be assigned
to the prior occupation in X2+ sites and the existence
of oxygen vacancy. This work not only provides a novel insight to
develop NIR-emitting Bi3+-activated phosphors but also
helps to reveal the underlying NIR luminescence mechanism of Bi3+ in inorganic compounds.
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