Green luminescence from Cu-diffused LiGaO2 crystals

Abstract

An intense green luminescence is observed from single crystals of LiGaO 2 doped with copper. Czochralski-grown undoped crystals are wrapped in thin copper foil and then held at 900 °C for 1 h in a flowing nitrogen atmosphere. Large concentrations of Cu + ions enter the crystals during this process and occupy Li + sites. These copper-diffused crystals are characterized with optical absorption, photoluminescence (PL), photoluminescence excitation (PLE), thermoluminescence (TL), and electron paramagnetic resonance (EPR). An optical absorption band peaking near 350 nm is assigned to the Cu + ions at Li + sites and represents an excitation from a 3d 10 ground state to a 3d 9 4s 1 excited state. A broad PL emission from these excited Cu + ions has a peak near 523 nm and the related PLE band has a peak near 356 nm (this PLE band links the emission to the optical absorption band). Illuminating a Cu-diffused crystal at room temperature with 325 nm laser light converts a portion of the Cu + ions to Cu 2+ ions. EPR spectra from these 3d 9 ions are easily seen at low temperatures and their angular dependence is used to determine the g matrix and the 63 Cu hyperfine matrix. Subsequent heating produces a TL peak near 122 °C with a maximum in its spectral dependence near 535 nm. Correlated EPR measurements show that this TL peak occurs when trapped electrons are thermally released from unintentionally present transition-metal ions (most likely Fe) and recombine with holes at the Cu 2+ ions.

Luminescence properties of LiGaO 2 crystal

“…Alloying of LiGaO2 with ZnO creates a material with a band gap tunable in 3.3e5.6 eV range [10]. Besides when doped with cupper ions this crystal was studied as a material for optically and thermally stim-ulated dosimetry [11].…”

“…Though many potential applications of LiGaO2 imply use of its optical properties there are not many studies of its luminescence characteristics. As to our knowledge, there are some works devoted to luminescence of dopants in LiGaO2, such as ions of Cr 3 þ [18,19], Cu þ [11], V 3 þ [4], but very few studies deal with luminescence of pure crystals e among them the early work of Dirksen [15], where the observed emission band at 360 nm and its excitation band at 220 nm were explained by charge transfer transitions between Ga and O ions, and the recent work [20] on luminescence of LiGaO2 nanoflakes with the same interpretation of the emission and excitation bands, located at lower energies compared to bulk crystal.…”

Multinary wurtzite-type oxide semiconductors: present status and perspectives

“…The first reported β-LiGaO 2 -based phosphor was β-LiGaO 2 :Fe 3+ , which emits deep red light near 740 nm [47]. Later studies reported β-LiGaO 2 :Cr 4+ [48] and β-LiGaO 2 :V 3+ [49], which respectively exhibited near-IR fluorescence near 1250 and 1700 nm, and β-LiGaO 2 :Cu + [50], which exhibited green fluorescence near 520 nm. Because the β-LiGaO 2 :Fe 3+ phosphor has a high internal quantum efficiency of ∼80% [47,51], it has recently received attention again as a red phosphor in solar simulators [51].…”

Advanced Thermoluminescence Spectroscopy as a Research Tool for Semiconductor and Photonic Materials: A Review and Perspective

“…[35,36] TL or TSL has been widely applied for measuring deep and relatively shallow traps in optical and photonic materials [37,38] and has been quite useful for optical studies of single crystals, films, phosphors, and transparent ceramics for lasers, scintillators, and solid-state lighting applications and more. [9,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] However, its applications in semiconductors has not been realized until recently [5,8,54] and are still very limited. The goal of this article is to explain the basics of TL, inform the reader about its capability as a great tool for measuring the energy levels of donors and acceptors in semiconductors, and bring the attention to the development of cryogenic thermally stimulated photoemission spectroscopy (C-TSPS) [55] which extends TL or thermally stimulated emission measurements to cover the entire range of shallow and deep levels in bandgap materials.…”