Review of Ga2O3-based optoelectronic devices

So far, a large number of rare earth (RE) and non-RE-doped emission-tunable crystals based on controllable energy transfer have become available, but numerous mechanistic issues, particularly for those that involve temperature-dependent energy transfer between the well-shielded 4f RE ions, lack comprehensive theoretical and experimental investigation, limiting greatly their development and applications in the future. Here, we design and report a type of Tb3+,Eu3+-doped Sr3Al2O5Cl2 phosphors capable of multiemissions upon excitation at 376 nm, through using the orthorhombic Sr3Al2O5Cl2 as the host lattice while the well-shielded 4f Tb3+ and Eu3+ ions as dual luminescent centers. Our results reveal that the energy transfer from Tb3+ to Eu3+ ions, happening via an electric dipole-quadrupole (d-q) interaction, can be controlled by the doping ratio of Tb3+ and Eu3+, leading to the tunable emissions from green (0.3159, 0.5572) to red (0.6579, 0.3046). It is found from time-resolved photoluminescence (PL) spectra that this energy transfer begins at t = 5 μs and gradually ends at t ≥ 200 μs. Moreover, from temperature-dependent PL results, we reveal that the Eu3+ emission features an anomalous intensity enhancement at the earlier heating state. With the density functional theory (DFT) calculations, we have screened the possibilities of site preferential substitution problem. By jointly taking into account the X-ray diffraction Rietveld refinement, DFT findings, and PL and thermoluminescence spectra, a mechanistic profile is proposed for illustrating the PL observations. In particular, our discussions reveal that the temperature-triggered Eu3+ emission enhancement is due to the interplay of the temperature-induced accelerated energy transfer and defect-trapped electrons that are released upon the thermal stimulation. Unlike most of reported phosphor materials that are always suggested for phosphor-converted white light-emitting diodes, we propose new application possibilities for Tb3+,Eu3+-doped Sr3Al2O5Cl2 phosphors, such as anticounterfeiting, temperature-controlled fluorescence sensor, data storage, and security devices.

Multicolor Tuning and Temperature-Triggered Anomalous Eu3+-Related Photoemission Enhancement via Interplay of Accelerated Energy Transfer and Release of Defect-Trapped Electrons in the Tb3+,Eu3+-Doped Strontium-Aluminum Chlorites.

In this study the optical spectroscopy, the excited state dynamics, and in particular the Tb3+ → Eu3+ energy transfer, have been investigated in detail both from the theoretical and experimental po...

Theoretical and Experimental Investigation of the Tb3+ → Eu3+ Energy Transfer Mechanisms in Cubic A3Tb0.90Eu0.10(PO4)3 (A = Sr, Ba) Materials

The garnet type phosphors of Eu3+ doped Ca3Ga2Ge3O12 were synthesized via conventional solid state reaction techniques. The phase purity and luminescence properties of the fabricated phosphors were characterized by X-ray powder diffraction, photoluminescence excitation and emission spectra, temperature dependent emission spectra as well as luminescence decay curves. The phosphors show enhanced red emission from a 5D0 → 7F4 transition of Eu3+ under the excitation of 394 nm. The unusual 5D0 → 7F4 intensity was explained by structural analysis. The emission intensity of the phosphors increases with the concentration of Eu3+ until the quenching concentration of 10 mol%. Excited by a pulsed laser of wavelength 610.8 nm, the emission intensity of the 5D0 → 7F4 transition increases monotonously as the temperature increases in the range of 160–360 K. The temperature dependent fluorescence behavior was investigated. The relative sensitivity reaches the maximum value of 3.66% K−1 at 160 K and reaches 1.04% K−1 at 300 K. The results show that the garnet type Ca3Ga2Ge3O12:Eu3+ phosphor is a promising material for the application of optical thermometry.

Enhanced 5D0 → 7F4 transition and optical thermometry of garnet type Ca3Ga2Ge3O12:Eu3+ phosphors

Synthesis condition and structural/luminescent properties of CaTiO3:Eu3+ red phosphor

This paper describes a method of generating low-distortion sinusoidal waves using an arbitrary waveform generator (AWG), and experimental results of using such a generator for ADC dynamic performance testing. With this proposed method, 3rd order harmonics of the generated signal are suppressed simply by changing the AWG program (or waveform memory contents)—AWG nonlinearity identification is not required—and spurious components, generated far from the signal band, are relatively easy to remove using an analog filter; our theoretical analyses, simulations, and experiments showed that a simple passive LC analog filter (with relaxed requirements compared to the one for direct HD3 removal) is sufficient. Our ADC testing results—using signals generated by an AWG with the proposed algorithm, and a simple passive LC LPF—show measurement errors (caused by 3rd order harmonics generated by AWG DAC nonlinearity) half that of previous algorithms.

Kenji Sawada

Papers

Low-distortion signal generation for ADC testing

Photoluminescence and resonant energy transfer from Tb3+ to Eu3+ in Tb3Ga5O12:Eu3+ garnet phosphor

Synthesis and properties of Ca3Ga2Ge3O12:Tb3+ garnet phosphor

Abnormal photoluminescence phenomena in (Tb3+, Eu3+) codoped Ga2O3 phosphor

Photoluminescence Properties of Eu3+ in Ga2O3−Tb3Ga5O12:Cr3+ Phosphor Synthesized by Metal Organic Deposition