Preparation And Luminescent Properities Of Two Novel Phosphor Materials For Warm White-LEDs

Currently, the commercially dominant approach of "InGaN blue chip+YAG:Ce³⁺ phosphor" for white light-emitting-diode ?w-LED? illumination generally suffers from red deficiency and poor thermal stability of organic encapsulants, which might result in cool white light, luminous degradation and chromatic aberration for the device after long-term working. Aiming to solve these problems, in this paper, we have designed two kind of materials for w-LED application. At first, the spectrally-modified YAG:Ce³⁺, Mn²⁺, Si⁴⁺ phosphor is prepared by doping Mn²⁺ as the red emitters and doping Si⁴⁺ as the charge compensators through a solid-state reaction route. Then, taking into consideration the factors that refractive index and density of the phosphor powders and precursor glass, a innovative precursor glass 55TeO₂-7B₂O₃-18ZnO-16Na₂O-4Al2O₃ ?mol%? is designed to form the PiG?Phosphor-in-Glass? composite with YAG:Ce³⁺, Mn²⁺, Si⁴⁺ phosphor. The high-power warm w-LED is constructed by coupling a PiG plate with the InGaN blue chip. Remarkably, the chromaticity coordinate of such w-LED can be well tuned to follow along the Planckian locus with the correlated color temperature ?Tc? evolving from cool white ?5541 K? to warm white ?3050 K?, color rendering index ?Ra? ?70, luminous efficiency ?LE? 40-100 lm/W, under a driving current of 350 mA. Besides, as a fact that red-emitting Mn⁴⁺activated oxide phosphors with cheap price and excellent physical/chemical stability has become a hot research topic for their potential applications in w-LED. We report a novel double-perovskite Gd₂ZnTiO₆:Mn⁴⁺ (GZT: Mn⁴⁺) red phosphor. The microstructures and luminescent properties of GZT:Mn⁴⁺ are studied in detail. How crystal-field strength and nephelauxetic effect influencing the Mn⁴⁺emission energy is also analyzed in this paper. Comparing to previously reported titanate perovskite MTiO₃ ?M=Sr, Ba?, the special crystal structure of GZT with alternatively slantwise arranged [TiO₆]/[ZnO₆] octahedrons brings two remarkble results: 1) [-Mn⁴⁺-O₂--Zn²⁺-] bond angle deviating from 180° results a decreased Mn⁴⁺ -O₂- bond covalency and leads a short wavelength emission; 2) Zn²⁺breaks the energy transfer chain between Mn⁴⁺ ions resulting in diminishment of the energy loss probability, which is beneficial to achieving efficient emission. After mixing the red-emitting GZT: Mn⁴⁺ with commercial blue and green phosphors and coupling the mixture with the 365 nm UV chip, we obtain a excellent w-LED with Tc=4742 K, Ra=82.9, R9=43.