Xin-Zhong Wang

A new single-component KCaY(PO4)2:Dy3+, Eu3+ nanosized phosphor with high color-rendering index and excellent thermal resistance for warm-white NUV-LED

In this study, novel KCaY(PO4)2:Dy3+, Eu3+ (KCYP:Dy3+, Eu3+) nanophosphor has been successfully prepared by a facile solution-combustion route. The crystal structure, morphological and microstructural features, and photoluminescence (PL) properties of KCYP:Dy3+, Eu3+ nanophosphor, as well as its thermal properties, have been studied. Investigations based on XRD, FTIR and Raman verify the formation of single-phased and well-crystallized KCYP:Dy3+, Eu3+. SEM and TEM observations reveal that the KCYP:Dy3+, Eu3+ nanophosphor displays uniform spherical morphology with an average particle size of about 47 nm. The optimal concentrations of Dy3+ and Eu3+ ions in KCYP were determined to be 3 mol% and 7 mol%, respectively. Under near-ultraviolet (NUV) excitation, individual Dy3+- or Eu3+-doped samples exhibit characteristic PL emissions in their respective regions. As for the Dy3+, Eu3+ co-doped KCYP, energy transfer has been confirmed happening from Dy3+ to Eu3+ via an electric dipole–dipole interaction, and the critical distance (Rc) was calculated to be 17.07 A. Our experiments reveal that it is easy to produce warm white or tunable emissions by regulating the Eu3+ content. Moreover, the single-component KCYP:3%Dy3+, 7%Eu3+ nanosized phosphor has a very low correlated color temperature (2766 K) and a high color-rendering index (Ra = 81.6). The quenching temperature (T0.5) of the KCYP:Dy3+, Eu3+ nanophosphor was found to be higher than 220 °C, indicating its superior thermal resistance. Consequent three rounds of the heating–cooling cycle experiments demonstrate no occurrence of thermal degradation. These findings suggest that this nanophosphor is a promising candidate for application in NUV-pumped glareless warm-white LED.

Color-tunable Al6Si2O13:Eu2+,Mn2+ phosphor with high color rendering index based on energy transfer for warm white LEDs

It is extremely necessary to develop LEDs with a high color index for many special applications. In this study, novel single-phase warm white light-emitting 3/2-mullite (Al6Si2O13):Eu2+,Mn2+ phosphors were prepared via the high-temperature solid-state reaction method. The emission hue can be precisely controlled from (0.2496, 0.3032) to (0.4001, 0.3031) by altering the Eu2+/Mn2+ ratio via the energy transfer route, where warm-white emissions with CIE coordinates of (0.3440, 0.3302) are achieved using UV-excited Al6Si2O13:2.0%Eu2+,0.6%Mn2+ phosphors. The energy transfer between Eu2+ and Mn2+ in the Al6Si2O13 host is demonstrated to be a nonradiative dipole–dipole interaction. A warm-white LED device comprising the Al6Si2O13:2.0%Eu2+,0.6%Mn2+ phosphor and an NUV (365 nm) chip operated at 120 mA yields white-light emissions with a correlated color temperature of 5656 K and color coordinates of (0.3289, 0.3413). Moreover, it should be noted that the color rendering indices of Ra and R9 can reach up to 92.4 and 97.0, respectively. Our proposed Al6Si2O13:2.0%Eu2+,0.6%Mn2+ phosphor with high color rendering index has good application prospects.