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A pn‐heterojunction is fabricated by depositing an n‐type β‐Ga2O3 film by pulsed laser deposition (PLD) on c‐cut Al2O3. P‐type cuprous oxide films, Cu2O, are then deposited by PLD, as well as by radio frequency (RF) magnetron sputtering. It is concluded that hole injection is prohibited by a 3.26 eV valence band barrier, as measured by X‐ray photo‐electron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Heterojunction diode structures are prepared on the front side and electrical measurements demonstrate a rectification ration of 8 orders of magnitude and an ideality factor close to 2, indicating interface recombination‐controlled forward current. The junction is also optically active and shows a very fast photo‐response to 275 nm UV light. [ABSTRACT FROM AUTHOR]

The authors report the third-harmonic generation, nonlinear refraction, and nonlinear absorption in HgS quantum dot (QD) suspensions and films using the nanosecond and femtosecond pulses. High conversion efficiency (7 × 10−4) towards the third harmonic (TH) of the 900–1700 nm, 150 fs laser in the thin (70 nm) films containing HgS QDs deposited on the glass substrates is obtained. The authors analyze spectral dependencies of the TH, nonlinear refractive indices, and nonlinear absorption coefficients of QDs in the 500–1700 nm range and discuss the relation between the TH process and the low-order nonlinear optical properties of these quantum dots. [ABSTRACT FROM AUTHOR]

For decades, materials with persistent luminescence (PersL) have triggered interest among scientists and industry. A considerable amount of research has been done on multiple commercially available materials emitting PersL in the blue and green spectral regions. Despite the wide variety of applications, the number of publications on the afterglow in the red spectral range is considerably lower. In pursuit of a competitive red PersL emitter, manganese doped Mg 2 SiO 4 , Mg 2 GeO 4, and their solid solutions of Mg 2 Si 1-x Ge x O 4 (x = 0.1–0.9) were prepared by the solid-state synthesis in ambient atmosphere. The materials were comprehensively analysed by X-ray diffraction (XRD), optical spectroscopy, thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR). Bright red PL and subsequent PersL of manganese ions in the red spectral region have been detected. In the case of the best persistent phosphor - Mg 2 Si 0.1 Ge 0.9 O 4 : 0.1 mol% Mn afterglow was detected for more than 16 h. Although both Mn2+ and Mn4+ are present in samples, only Mn2+ related PersL with broadband emission between 600 and 800 nm and a maximum around 640 nm is observed. An in-depth analysis of TSL measurements showed that three distinct trap centres with trap depth values of 0.87 eV, 0.99 eV, and 1.84 eV are present in the material. Additionally, a quasi-continuous distribution of closely overlapping trap levels appears with trap depth values around 1.1–1.8 eV. EPR measurements have confirmed the presence of two distinct charge traps associated with trapped hole O− and trapped electron F+ centres. The thermal stability of these centres was analysed and correlated to PersL processes. • The luminescence of Mn-doped Mg 2 SiO 4 –Mg 2 GeO 4 system is reported for the first time. • Bright red Mn4+ photoluminescence has been observed under UV excitation. • Red Mn2+ persistent luminescence has been observed after irradiation with UV. • The system of discrete and continuous traps has been demonstrated. • Oxygen-related traps have been linked to charge traps. [ABSTRACT FROM AUTHOR]

Persistent luminescence (PersL) is a phenomenon when a material continues to emit light for a period of time, usually several minutes or hours after the removal of the excitation source. Although it is possible to find several hundred different materials suitable for the observation of PersL in the visible part of the spectrum, only a handful of them is applied to obtain phosphors for near infrared (NIR) emission. In the course of this work, CaZnGe 2 O 6 : Cr3+, M3+ (M3+ = B3+; Al3+; Ga3+) materials have been synthesized by a melt crystallization method. Photoluminescence (PL) and subsequent PersL of chromium ions in the NIR spectral region, as well as visible PL and PersL of the host material, have been observed. After irradiation with ultraviolet (UV) radiation, a broad NIR PersL band with a maximum around 790 nm and an afterglow time over 1 h has been detected. The addition of B3+; Al3+; Ga3+ increases the overall intensity and duration of PersL. The analysis of PersL decay curves and glow curves of thermally stimulated luminescence (TSL) show multiple trap centres involved in the generation of PersL. • CaZnGe 2 O 6 : Cr3+, M3+ (M3+ = B3+; Al3+; Ga3+) material has been synthesized. • Near infra-red long persistent luminescence lasting over 1 h has been observed. • Adding co-dopants increases the integral intensity of the PersL up to 1.8 times. • Continuous trap distribution was revealed with trap depths from 0.8 to 1.1 eV. [ABSTRACT FROM AUTHOR]