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The Eu3+-doped α-Al2O3 micro/nano-biscuits were prepared via microwave/starch- assisted sol-gel approach. The typical sample had the pure hexagonal α-Al2O3 phase. The solubility limit of Eu3+ ions was ~ 2 mol%. The micro/nano-biscuits consisted of the outer layers paved with nanoparticles of 50–70 nm and inner layers arranged with nanoparticles of 100–200 nm in a brick-upon-tile pattern. The forming mechanism was proposed. Optical bandgap values were apparently lower than that of bulk Al2O3 (~ 8.7 eV), assigned to appearance of some defect levels and incorporation of impurity ions. The critical distance was ∼ 15.95 A and ET mechanism was the d-d interaction. The integrated strength at 423 K dropped to 68% of the original value at 298 K and the E a was ~ 0.259 eV. Moreover, the CIE coordinate of the typical sample with good thermal stability was close to that of the commercial red phosphor, having promising applications in pc-WLEDs as a red-emitting phosphor.

CaAl12O19: Mn4+ has been reported as a red phosphor with good color purity. A quaternary-doping strategy was adopted to improve the optical properties in this work. Phosphors of general formula Ca1-mAl12-x-y-nO19: xMn4+, yMg2+, mBi3+, nB3+ (CAO:MMBB) were synthesized by high-temperature solid-state method. A broad band deep-red emission from Mn4+ centered at 654 nm was observed, and two strong absorption bands within the ultraviolet range (350–400 nm) and blue-green region peaked at 460 nm were confirmed. The incorporation of co-dopants brought about a remarkable enhancement of the luminescence intensity. The quantum yield of CAO:MMBB reached 84.9%, which is approximately 1.35 times higher than that of as-reported binary-doping phosphors CaAl12-x-yO19: xMn4+, yMg2+ (CAO:MM). The possible mechanism of co-doping Bi3+ and B3+ ions was discussed in detailed. CAO:MMBB phosphor shows a dual application in agriculture either as solar spectral conversion auxiliary in greenhouse plastic films or as a red component in blue-chip based plant growth light emitting diodes (PG-LEDs).

The red phosphors Mg2TiO4:Mn4+, Bi3+, Li+ with strong absorption at blue region were synthesized. Through the excitation and emission spectra, diffuse reflection spectra and Raman spectra, it is proved that Bi3+ ion plays a role of sensitizer to the enhancement of optical property, especially the increased excitation intensity of blue light. It is the first time to report about asynchronous increases of different excitation bands with Bi3+ as a sensitizer, primarily resulting from the perturbation of symmetry and lattice vibration along with crystal defect in the host lattice with larger Bi3+ occupied at a small octahedral site of Mg2+. The sensitization of Bi3+ works not only in the case of powder phosphors but also even better in ceramic phosphors. For powder phosphor, the intensity of the blue excitation band of Mg2−2xTi0.999O4:0.1%Mn4+, xBi3+, xLi+ grows to at least 1.5 times than that of Mg2Ti0.999O4:0.1%Mn4+ when x = 0.5%, following with a uplift at about 410 nm. Meanwhile, Mg2TiO4:Mn4+, Bi3+, Li+-based luminescent ceramic manifests with a more than 2.5 times increase as x = 0.8%. The red phosphors with a broad emission band in the pure red light region show a promising application in blue LEDs as a red component.

High temperature sensitivity phosphor based on an old material red emitting CaTiO3: Pr3+ phosphor prepared via H3BO3 flux assisted solid-state reaction is reported. The typical sample possesses the orthorhombic perovskite phase and no impurity is found. The optical bandgap value is ~3.59 eV. There exists a single red emission with ideal color purity. The average long-afterglow decay time is 87.7s, the average trap depth is 0.76 eV. The maximum absolute sensitivity at 473 K is equal to ~0.0258 K-1 and the maximum relative sensitivity is estimated to be 7.69% K−1 at 298 K with the resolution of 0.26–0.65 K, indicating the suitability of the material for temperature sensitivity application. A possible mechanism for the quenching of 3Pj emission at room temperature and the thermal quenching process of 1D2 level through intervalence charge transfer state are proposed from the configurational coordinate diagram.

In this work, we report preparation, characterization and luminescent mechanism of a phosphor Sr 1.5 Ca 0.5 SiO 4 :Eu 3+ ,Tb 3+ ,Eu 2+ (SCS:ETE) for white-light emitting diode (W-LED)-based near-UV chip. Co-doped rare earth cations Eu 3+ , Tb 3+ and Eu 2+ as aggregated luminescent centers within the orthosilicate host in a controlled manner resulted in the white-light phosphors with tunable emission properties. Under the excitation of near-UV light (394 nm), the emission spectra of these phosphors exhibited three emission bands: one broad band in the blue area, a second band with sharp lines peaked in green (about 548 nm) and the third band in the orange–red region (588–720 nm). These bands originated from Eu 2+ 5d→4f, Tb 3+ 5 D 4 → 7 F J and Eu 3+ 5 D 0 → 7 F J transitions, respectively, with comparable intensities, which in return resulted in white light emission. With anincrease of Tb 3+ content, both broad Eu 2+ emission and sharp Eu 3+ emission increase. The former may be understood by the reduction mechanism due to the charge transfer process from Eu 3+ to Tb 3+ , whereas the latter is attributed to the energy transfer process from Eu 2+ to Tb 3+ . Tunable white-light emission resulted from the system of SCS:ETE as a result of the competition between these two processes when the Tb 3+ concentration varies. It was found that the nominal composition Sr 1.5 Ca 0.5 SiO 4 :1.0%Eu 3+ , 0.07%Tb 3+ is the optimal composition for single-phased white-light phosphor. The CIE chromaticity calculation demonstrated its potential as white LED-based near-UV chip.