Mn Phosphor Thin Films Research Articles

Enhanced photoluminescence in epitaxial ZnGa2O4:Mn thin-film phosphors using pulsed-laser deposition

The growth and properties of ZnGa2O4:Mn thin-film phosphors on single crystal substrates using pulsed-laser deposition were investigated. Epitaxial film properties were compared to polycrystalline films deposited on glass substrates. Green photoluminescence was observed for as-deposited films with no postannealing required. Enhanced luminescent intensity in the epitaxial films was observed as compared to randomly oriented polycrystalline films, suggesting that grain boundaries and grain alignment strongly influence the luminescent properties. The ratio of Zn/Ga in the films also affected photoluminescence properties, with strong green emission observed in Zn-deficient films.

Pulsed KrF laser annealing of RF sputtered ZnS:Mn thin films

Pulsed KrF laser annealing (PLA) of ZnS:Mn thin (800 nm) film phosphors has been investigated as an alternative to thermal annealing for the fabrication of electroluminescent devices. The influence of the surrounding gas pressure during exposure, the energy density (Ed) of the laser beam and the effect of double irradiation is reported. Luminescent properties as function of laser energy density (Ed) are determined via photoluminescent (PL) characterisation. Energy densities used vary from 53 to 777 mJ/cm 2. PL intensities are determined to be linearly dependent with Ed beyond a threshold of 150 mJ/cm 2 and maximum PL enhancement is a factor of 2.1 x. A thermal simulation of the PLA process suggest that PL improvement is proportional to deposited thermal energy and this in the solid state. The calculated melting threshold agrees well with previous work.

Luminescence decay kinetics in homogeneously and delta-doped ZnS:Mn

The luminescence decay kinetics of homogeneously and delta-doped ZnS:Mn thin film phosphors was investigated. A quantitative model based on the hopping model of energy transfer theory was developed to described the concentration quenching phenomenon in ZnS:Mn. The model predicted the dependence of the energy transfer rate on material parameters such as the Mn and defect concentrations. The luminescence decay of homogeneously doped ZnS:Mn consisted of two exponential components at 10 K. The fast component of 120 μs was attributed to exchange-coupled pair emission and the slow component of 1.6 ms to isolated Mn ions. As the temperature was increased, the exchange-coupled pair emission disappeared and the decay became strongly nonexponential. The nonexponentiality was attributed to nonradiative energy transfer processes. The concentration dependence of the effective lifetime was also found to change with temperature. The investigation on the temperature dependence revealed two regimes of concentration which showed distinct temperature dependencies. From the temperature dependence, it was concluded that the energy transfer between Mn ions was active only when the Mn concentration was greater than 2 at. %. By comparing these results with the results of Dexter’s theory, the energy transfer between Mn ions was found to be mediated by an electric dipole–dipole interaction. The delta-doped ZnS:Mn showed faster decay times due to the enhanced overlap between 3d and s-p host states caused by lattice strain. From the temperature dependence, a two-dimensional confinement of energy transfer was observed when the doping planes were far apart. However, when the doping planes were brought close together, the delta-doped samples behaved similarly to the homogeneously doped ZnS:Mn indicating that the energy transfer was no longer two-dimensionally confined.

TFEL devices using oxide thin films without vacuum process

Abstract Thin-film electroluminescent (TFEL) device fabrication using solution coating techniques which eliminate the need for vacuum processes have been demonstrated. The oxide phosphor thin-film emitting layer and the transparent conducting oxide thin-film electrode were prepared by this less expensive deposition process using metallic complex salts which are low in cost and easy to handle. TFEL devices with dip-coated ZnGa2O4:Mn, Ga2O3:Mn and CaGa2O4:Mn phosphor thin films were compared to devices with sputtered phosphor thin films. TFEL devices with a dip-coated ZnGa2O4:Mn or Ga2O3:Mn thin-film emitting layer exhibited higher luminance than equivalent devices with sputtered thin-film emitting layers: a luminance maximum above 750 or 1000 cd/m2 in green emission, respectively, when driven at 1 kHz.

Preparation of ZnGa2O4:Mn phosphor thin films as emitting layers for electroluminescent devices

ZnGa2O4:Mn thin films as the emitting layer in thin-film electroluminescent (TFEL) devices have been prepared by rf magnetron sputtering and low-pressure chemical vapor deposition (CVD). The as-deposited thin films, regardless of preparation methods, were ZnGa2O4 which crystallized with a spinel structure. A green EL emission was realized in TFEL devices using as-deposited ZnGa2O4:Mn thin films as the emitting layer and a thick BaTiO3 ceramic sheet as the insulating layer. Maximum luminances of 0.7 and 7.6 cd/m2 were obtained in TFEL devices using as-deposited ZnGa2O4:Mn thin films prepared by the sputter and CVD techniques, respectively, when driven by a sinusoidal wave voltage at 1 kHz. In addition, a maximum luminance above 600 cd/m2 was obtained in TFEL devices using ZnGa2O4:Mn thin films postannealed at a temperature of about 1000 °C, regardless of preparation methods. The improvement of EL characteristics by postannealing ZnGa2O4:Mn thin-film emitting layers was mainly attributed to an improvement in the crystallinity of the emitting layers.