To further understand the energy loss mechanism of the ＂charge transfer process＂ that was proposed in our previous work on Eu^2＋-Mn^2＋ co-doped phosphors, the influence of synthetic temperature and heating time on the photoluminescence（PL） behavior of M5（PO4）3Cl：Eu^2＋,Mn^2＋（M=Ca, Sr） phosphors was investigated by analyzing their PL spectra and decay curves. For the Ca phase, an increase in the synthetic temperature resulted in an increase in the loss from the ＂charge transfer process＂ since more Eu^2＋ ions were involved in the Eu^2＋-Mn^2＋ clusters. This was contrary to the thermodynamic expectation. To solve this contradiction, we proposed that the formation of Eu^2＋-Mn^2＋ clusters was kinetically blocked at lower synthetic temperatures. With an increase in heating time for the phosphors synthesized at lower temperature（such as 1100 ℃） the PL intensity decreased, which supported the above assertion.
采用高温固相法合成Ca取代Sr3Al0.6Si0.4O4.4F0.6∶Ce3+中Sr的Sr3-x Ca x Al0.6Si0.4O4.4F0.6∶Ce3+荧光粉。由于Sr3Al0.6Si0.4O4.4F0.6∶Ce3+中Sr具有十配位Sr(1)和八配位Sr(2),所以激活剂离子Ce3+也具有两个不同的占位。结合Ce3+的光谱结果和Van Uitert经验公式,分别研究了十配位Ce(1)3+和八配位Ce(2)3+的猝灭浓度和荧光寿命,指出是由于Ca的掺入减小了Ce(1)3+发光中心,增加了Ce(2)3+发光中心,从而出现随着Ca/Sr比增加,样品在400 nm激发下发光强度减小,而在460 nm激发下发光强度增大的现象。同时,Ca的掺入增强了粉体发光的热稳定性。调节Ca含量可以使粉体实现从绿黄色到黄色的发光,表明Sr3-x Ca x Al0.6Si0.4-O4.4F0.6∶Ce3+荧光粉是一款潜在的适合近紫外和蓝光激发的白光LED用荧光粉。
Y3Al5O12:Ce3+ is the most famous phosphor material due to its excellent photolumincent properties.Here,through first-principles calculation,the effect of carbon interstitial defects on Y3Al5O12:Ce3+phosphor was investigated. It is found that the carbon interstitials tend to occupy the next-nearest sites of Ce3+ion in Y3Al5O12:Ce3+ lattice. Specially,these interstitial defects can shorten the Ce3+-O2-bond length, leading to a larger crystal field splitting of 5 d orbital of the Ce3+atom and bigger 5 d centroid shift.These two factors cause the emission spectrum of Y3Al5O12(C):Ce3+red shift compared with that of Y3Al5O12:Ce3+. Moreover, with our comparison experiment, we find that the Y3Al5O12(C):Ce3+ has an obvious red shift compared with that of Y3Al5O12:Ce3+system,which is in accord with our first principles calculation. Our work systematically investigates the impact of the carbon interstitial defect on Y3Al5O12:Ce3+,and provides a new route to tune the emission spectrum in Y3Al5O12:Ce3+.
The novel nitride-based luminescent materials have received much attention since the end of the last century. In this paper, the commercial Eu2＋-activated nitride red phosphors, Sr1.95Si5N8：Eu0.05, Sr1.85Si5N8：Eu0.15 and Ca0.99AlSiN3：Eu0.01 phosphors were an-nealed at different temperatures （beyond 300 oC） to investigate the dependence of their luminescence performance and structure vari-ability on the temperature. By photoluminescence spectra, X-ray diffraction （XRD） and thermogravimetry-differential scanning calo-rimetry （TG-DSC） analysis, the high temperature stability of the hosts and activator of the three samples were disclosed. With the an-nealing temperature increasing, the activator Eu2＋ions were firstly oxidized and then host in Sr1.95Si5N8：Eu0.05 and Sr1.85Si5N8：Eu0.15, but for Ca0.99AlSiN3：Eu0.01, only the oxidation of the host could be observed, which would lead to the luminescence degradation and even failure of these phosphors. The activator Eu2＋ions were much more stable in CaAlSiN3：Eu than Sr2Si5N8：Eu due to their crystal surroundings, and its concentration also influenced the temperature stability of Sr2Si5N8：Eu.
Green emitting Eu^2＋ doped（CaxSr（1–x））6Si（25.6）Al（6.4）N（41.6）O（4.4） phosphors with x value ranging from 0 to 0.1 were synthesized by the solid state reaction method under nitrogen atmosphere.The X-ray diffraction（XRD）patterns of the phosphors with different Ca^2＋ concentrations indicated that pure sialon phases were obtained.Crystal structure of these sialon phases was estimated to be a commensurate composite network stacking by two different types of layers.Intense and tunable green emissions with a slight red shift from 515 to 520 nm were observed with varying Ca/Sr ratios.The emission intensity decreased gradually because of the increase of the crystal splitting effect.Thermal quenching properties of the phosphors with different Ca^2＋ saturation were also discussed.The thermal stability became worse as more Ca^2＋ ions substituted for Sr^2＋ ions according to a larger Stokes shift.The solid solution phosphors could be a promising candidate for white LEDs for their interesting photoluminescence properties when the thermal stability would be improved.
Red phosphor K2LiA1F6：Mn4＋ has been synthesized by a cation-exchange method in HF solution. To optimize their optical properties, phosphors were synthesized using different reaction conditions. The K2LiA1F6：0.5%Mn4＋ synthesized at 20℃ for 4 h shows the highest luminescence intensity. The temperature-dependent emission intensity of the phosphor was investigated, and it was found to exhibit good thermal stability, making it a promising red phosphor candidate for warm WLEDs.
Novel red-emitting Eu3＋, Sm3＋ singly doped and co-doped Ca14Mg2（SiO4）8 phosphors were prepared by conventional solidstate reaction. Powder X-ray diffraction patterns were employed to confirm phase pttrity. Ca14Mg2（SiO4）8：Eu3＋ phosphors exhibited intense red emission under 394 nm excitation and Ca14Mg2（SiO4）8：Sm3＋ phosphors, excited at 405 nm, also showed strong red emitting at 602 nm. The concentration quenching mechanism of Cal4Mg2（SiOa）s：Eu3＋ was dipole-dipole interaction, while that of CalnMg2（SiOn）8：Sm3＋ was energy migration among nearest neighbor ions. The results indicated that Ca14Mg2（SiOn）8：Eu3＋ and Ca14Mg2（SiOn）s：Sm3＋ were promising red-emitting phosphors for WLEDs. Meanwhile, the effect of co-doping Sm3＋ ions on photoluminescence properties of CalaMg2（SiO4）s：Eu3＋ was studied and energy transfer from Sm3＋ to Eu3＋ was discovered in Eu3＋, Sm3＋ co-doped phosphors.
