Tongtong Xuan

Facile synthesis, morphology and photoluminescence of a novel red fluoride nanophosphor K2NaAlF6:Mn4+

A novel red-emitting fluoride phosphor, K2NaAlF6:Mn4+, with nanoscale particle size was synthesized via a cation exchange route. This phosphor absorbs UV and blue light and emits red light at about 630 nm; thus, it has been regarded as an ideal red phosphor for WLEDs. The reaction parameters were systematically investigated and an optimized sample was obtained. K2NaAlF6:Mn4+ showed better photoluminescence properties and its emission wavelength was blue shifted with respect to that of K2LiAlF6:Mn4+ due to differences in the neighbouring alkali metal ions and different distances between the cation and the ligands. These results are in agreement with the trend determined by the recently introduced parameter β1, which describes the energy of the 2Eg → 4A2g transition as a function of the nephelauxetic effect. Finally, these results could further contribute to the optimization of red-emitting phosphors based on Mn4+ ions.

Photoluminescence properties of a novel red fluoride K2LiGaF6:Mn4+ nanophosphor

Red K2LiGaF6:Mn4+ phosphors have been synthesized by the facile cation-exchange method. To optimize the optical properties, the phosphors were synthesized by using different reaction conditions. The highest luminescence intensity was increased 3.6 times for the Mn concentration of 1%, reaction temperature of 20 °C, and reaction time of 1 h. Replacement of the trivalent Al by Ga resulted in K2LiGaF6:Mn4+ having better photoluminescence properties than K2LiAlF6:Mn4+. Furthermore, the studies of the temperature-dependent emission intensity of the phosphors confirmed their good thermal stability, making them promising red phosphor candidates for white light-emitting diodes.

Highly Stable K2SiF6:Mn4+@K2SiF6 Composite Phosphor with Narrow Red Emission for White LEDs

Poor water resistance and nongreen synthesis remain great challenges for commercial narrow red-emitting phosphor A2MF6:Mn4+ (A = alkali metal ion; M = Si, Ge, Ti) for solid-state lighting and display. We develop here a simple and green growth route to synthesize homogeneous red-emitting composite phosphor K2SiF6:Mn4+@K2SiF6 (KSFM@KSF) with excellent water resistance and high efficiency without the usage of toxic and volatile hydrogen fluoride solution. After immersing into water for 6 h, the as-obtained water-resistant products maintain 76% of the original emission intensity, whereas the emission intensity of non-water-resistant ones steeply drops down to 11%. A remarkable result is that after having kept at 85% humidity and at 85 °C for 504 h (21 days), the emission intensity of the as-obtained water-resistant products is at 80-90%, from its initial value, which is 2-3 times higher than 30-40% for the non-water-resistant products. The surface deactivation-enabled growth mechanism for these phosphors was proposed and investigated in detail. We found that nontoxic H3PO4/H2O2 aqueous solution promotes the releasing and decomposition of the surface [MnF6]2- ions and the transformation of the KSFM surface to KSF, which finally contributes to the homogeneous KSFM@KSF composite structure. This composite structure strategy was also successfully used to treat KSFM phosphor prepared by other methods. We believe that the results obtained in the present paper will open the pathway for the large-scale environmentally friendly synthesis of the excellent antimoisture narrow red-emitting A2MF6:Mn4+ phosphor to be used for white light-emitting diode applications.

Co-precipitation synthesis and photoluminescence properties of BaTiF6:Mn4+:an efficient red phosphor for warm white LEDs

The investigation of efficient red phosphors is highly desired for the development of novel warm white light emitting diodes (WLEDs). In this paper, we report on an efficient red phosphor of Mn4+-activated BaTiF6 by a facile co-precipitation method as a promising candidate for warm white LEDs. BaTi1−xF6:xMn4+ phosphors show efficient pure red emission with a high quantum yield (QY) of 44.5% under 460 nm excitation. The BaTi1−xF6:xMn4+ phosphor exhibits a number of advantages. Firstly, the corresponding excitation/absorption profile matches the commercial blue LED chip well. Secondly, it also exhibits appropriate CIE coordinates (x = 0.694, y = 0.306) with an activation energy of 0.603 eV. The demonstration of a blue chip combined with a blend of yellow-emitting YAG:Ce3+ and newly developed BaTi0.97F6:0.03Mn4+ red phosphor greatly improved the colour rendering index (CRI) from 69.9 to 83.5, while significantly decreasing the correlated colour temperature (CCT) from 5088 to 4213 K, thus validating their application in warm white LEDs.

Nanocomposites of CsPbBr3 perovskite nanocrystals in an ammonium bromide framework with enhanced stability

Herein, we report a new highly luminescent material, a CsPbBr3@NH4Br (CPBr–NB) nanocomposite, formed via an ion-exchange reaction, which can reach up to a few micrometers in size. The CPBr–NB solid-state luminophores with a unique core@shell structure effectively avoid photoluminescence quenching and maintain excellent optical properties of the perovskite nanocrystals. Most importantly, the nanocomposite exhibits excellent water resistance and thermal stability. Such superior optical merits endow them with promising potential in lighting and displays.

Synthesis of Eu2+/Eu3+ Co-Doped Gallium oxide nanocrystals as a full colour converter for white light emitting diodes

Eu2+ and Eu3+ co-doped Ga2O3 nanocrystals (Ga2O3:Eu NCs) were synthesized in an organic phase at a low reaction temperature of 300 °C. The surface of Ga2O3:Eu NCs was passivated by oleylamine (OAm) and acetylacetone (acac). The coexistence of Eu2+ and Eu3+ as well as passivation by acac and OAm enable Ga2O3 to be excited in the broad spectral range of 200-500 nm. The broadened absorption band is attributed to the strong acac → Ln(III) ligand to the metal charge transfer transition at ∼370 nm, Eu(III) f-f allowed 7F0 → 5L6 transition at 395 nm, and 7F0 → 5D2 transition at 465 nm, as well as the efficient electronic transition of Eu(II) 4f → 5d at ∼400 nm. Under near-ultraviolet excitation, white light emission can be achieved by combining orange-red light from f-f electronic transition of Eu(III) with blue-green-yellow light from Ga2O3 oxygen defects levels. Furthermore, the resultant Ga2O3:Eu NCs with optimized quantum yield of 14.5% were coated onto 395 nm near-ultraviolet chips to fabricate a white light emitting diode. It exhibits a luminous efficiency of 34 lm/W, CIE colour coordinate of (0.2964, 0.2831) and high colour rendering index of 80.