Narrow Results

Novel deep red phosphor Li₂MgGeO₄:Mn⁴⁺ is synthesized by high temperature solid state reaction method in air. The strongest PL band peaking at ~ 671 nm in the range of 600–750 nm is due to the ²E → ⁴A₂ transition of Mn⁴⁺ ion and the PLE spectra shows broad band peaking at ~ 323 within the range 220–550 nm owing to the ⁴A₂ → ⁴T₁ transitions of Mn⁴⁺ ion. The optimum Mn⁴⁺ doping concentration is about 0.4 mol.%. The luminous mechanism is explained by Tanabe–Sugano diagram of Mn⁴⁺ ion. The results indicate that red phosphor Li₂MgGeO₄:Mn⁴⁺ is a beneficial phosphor for use in white light-emitting-diodes (LEDs).

Long afterglow CaTiO₃:Pr${}^{3+}$ ceramic powders were integrated with hydrothermal TiO₂ nanocrystallites via “doctor-blade” and TiO₂-CaTiO₃:Pr${}^{3+}$ hybrid thick films on FTO substrate were fabricated. Effects of the Pr${}^{3+}$ doping level (0.06%, 0.3%) and the CaTiO₃:Pr${}^{3+}$/TiO₂ weight ratio (0.23, 0.92) on the crystallinity, morphologies, optical transmittance and photoluminescence (PL) properties were investigated. Results showed that the crystallinity of the hybrid films originated from both TiO₂ nanocrystallites and CaTiO₃:Pr${}^{3+}$ ceramic particles, affected little by the integrating process. The film surface became denser and coarser due to the incorporation of CaTiO₃:Pr${}^{3+}$ micron/submicron particles, and the film thickness varied little ($\sim$2.2$\mu$m). The optical transmittance of the hybrid film decreased sharply ($<$20% for 0.92 incorporation level) due to the scattering effects of the CaTiO₃:Pr${}^{3+}$ micron/submicron particles to the incident light. All the hybrid films exhibited strong PL at $\sim$613nm when excited with 332–335nm, and the film with the Ca${}_{0.997}$TiO₃:Pr${}_{0.003}^{3+}$/TiO₂ weight ratio of 0.23 showed the highest emission. In addition, the film exhibited a photoresponce to a broad ultraviolet excitation ranging from 288–369nm and a long emission decay time up to 30min at 613nm, possible for use in the ultraviolet detectors, solar cells and other photoelectrical devices.

An oxide red phosphor, with outstanding superiority in manufacturing cost, is particular desired for white light-emitting diodes (LEDs). In this work, a strategy to controllable site occupation of Eu in Sr₃Al₂O₆ to give red light emission was employed with a three-step route: the combustion of sol–gel to prepare superfine precursor, the solid-sate reaction of precursor to incorporate Eu into small voids, and a second reduction in 25%H${}_2+$75%N₂ atmosphere. Accordingly, a new red phosphor of Sr₃Al₂O₆:Eu,Dy,Li was developed. The results shows the red luminescence of Sr₃Al₂O₆:Eu could be improved by doping Dy${}^{3+}$ and be further improved by co-doping Li${}^{+}$. The red luminescence involves the $4f$-$5d$ transition of Eu${}^{2+}$ and the auto-ionization of electron from Eu${}^{2+}$ to conduction band. Dy${}^{3+}$ acts as a trap center of the thermally released electrons then with electrons returned to the 4$f$ ground state of Eu${}^{2+}$, red light was emitted. The co-substitution of Sr${}^{2+}$–Sr${}^{2+}$ by Dy${}^{3+}$–Li${}^{+}$ is helpful to balance defects and improve crystallization.