Anti‐Thermal‐Quenching Bi³⁺ Luminescence in a Cyan‐Emitting Ba₂ZnGe₂O₇:Bi Phosphor Based on Zinc Vacancy

Abstract

Thermal quenching (TQ) of phosphor is one of the biggest challenges to develop high‐quality white light‐emitting diodes (w‐LEDs). Herein, an anti‐thermal‐quenching (anti‐TQ) property in cyan‐emitting Ba2ZnGe2O7:Bi3+ phosphor is reported. At 150 °C, its emission intensity increases to 114% of the original intensity at 25 °C. Especially, the integrated emission intensity reaches 138%, 148%, and 134% at 150, 200, and 250 °C, respectively, by artificially creating zinc and oxygen vacancy defect. The anti‐TQ phenomenon is mainly attributed to high structure rigidity and strong ability to compensate emission loss during thermal generation process. Thermal‐induced emission compensation mainly stems from self‐oxidization behavior of Bi2+ in zinc vacancy and the presence of oxygen vacancy defect. Oxygen vacancy is induced by native zinc vacancy and charge imbalance between Bi3+ and Ba2+ ions. The strategy to create oxygen vacancy defect and design self‐oxidization process of Bi opens a new insight to exploit anti‐TQ phosphors for high‐quality w‐LEDs applications.

Gradient defects mediate negative thermal quenching in phosphors

“…In a PALS experiment, a 22 Na radioactive source was used as the positron source with a source intensity of about 13 μJ. Two identical samples were clamped on either side of a 22 Na source to form a typical sandwich geometry.…”

“…Owing to energy compensation of a single-defect zinc vacancy, Li et al. reported that the emission intensity of a cyan phosphor Ba2ZnGe2O7:Bi3+ at 423 K was 114% of that at RT, 22 and its thermal stability was further improved after the introduction of oxygen vacancies by reductive atmosphere treatment. Qiu et al.…”

“…19 Under increasing temperatures, the charge carriers stored in the defects could be thermally released and transferred to the luminescence centers, thus compensating for the emission loss due to nonradiative transition. 20,21 Kim et al reported a cation vacancy-induced phase transition with energy transfer (ET) from the defect to the Eu 2þ 5d-bands in Na 3 Sc 2 ðPO 4 Þ 3 ∶Eu 2þ phosphor, achieving zero TQ at 473 K. 7 Owing to energy compensation of a singledefect zinc vacancy, Li et al reported that the emission intensity of a cyan phosphor Ba 2 ZnGe 2 O 7 ∶Bi 3þ at 423 K was 114% of that at RT, 22 and its thermal stability was further improved after the introduction of oxygen vacancies by reductive atmosphere treatment. Qiu et al reported that a deeper defect structure Tm : Sr formed by substituting Sr 2þ with Tm 3þ in Sr 3 SiO 5 ∶Eu 2þ led to zero TQ at 393 K. 23 In general, the more diverse and deeper the defects, the more carriers could be captured and the more energy could be transferred from the defects to luminescence centers.…”

Modulation of Bi3+ luminescence from broadband green to broadband deep red in Lu2WO6 by Gd3+ doping and its applications in high color rendering index white LED and near-infrared LED

“…For the fabrication of pc-WLEDs, one typical route is to combine red-green-blue (RGB) emitting phosphors with a UV LED chip or to pump a blend of red and green phosphors with a blue LED chip. 5,6 However, due to the lack of a cyan (470-510 nm) spectral component between the PL spectra of blue and green phosphors, the obtained pc-WLEDs have a low color rendering index (CRI, 70-80), which limits their wide application in general lighting. 7,8 For addressing the cyan gap, developing UV or blue light excitable cyan-emitting phosphors has become a logical solution, and thus considerable attention has been paid to the synthesis of cyan-emitting phosphors to enhance the CRI of pc-LED devices.…”

Enabling narrowband cyan photoluminescence and long-lasting ultraviolet-A persistent luminescence in Bi3+ single-doped Sr3Sc2Ge3O12 phosphors by selective site occupation

“…[13][14][15][16] For example, for phosphor-converted white LED applications, most Bi 3+ -doped phosphors usually show broad absorption bands in the UV region due to the transition from the 1 S 0 ground state to the 3 P 1 excited state and emit tunable colors in the visible spectral region. 17,18 The avoidance of spectral overlap between their excitation and emission bands can reduce the efficiency loss and greatly increase the luminous efficiency. 19,20 Moreover, tunable emission wavelength can be precisely realized by varying the host composition and crystal structure.…”