Photoluminescence Degradation Research Articles

Origin of Persisting Photoresponse of One-Year Aged Two-Dimensional Lead Halide Perovskites Stored in Air under Dark Conditions.

Two-dimensional halide perovskites are promising for advanced photonic, optoelectronic, and photovoltaic applications. However, their long-term stability is still a critical factor limiting their implementation into further commercial applications. Here, we present an environmental stability analysis of BA2(MA)n-1PbnI3n+1 (BA = C4H12N+, MA = CH6N+) two-dimensional perovskites with the lowest quantum well thicknesses of n = 1 and n = 2, after 1 year of aging under ambient humidity, oxygen content, and light conditions. We observed that both crystal phases (n = 1 and 2) degraded similarly, resulting in the removal of organic components and crystal decomposition into PbI2, Pb oxides, and Pb hydroxides. However, we have found a significant difference between their aging under ambient light and dark conditions, affecting their degraded morphology and photoactivity. Both crystal phases exposed to ambient light aged into a morphology characterized by the formation of several pinholes and voids, accompanied by photoluminescence degradation. Samples stored under dark conditions surprisingly preserved their photoluminescence activity, which morphologically aged into microrod structures. We conclude that the observed loss of photoactivity of 2D perovskites aged under ambient light is attributed to photoaccelerated degradation processes causing faster crystal surface photo-oxidation accompanied by a creation of multiple I vacancies and hydration of the inner crystal. The retainment of photoactivity in 2D perovskites aged under dark conditions is attributed to slower surface oxidation processes into Pb salts, as confirmed by X-ray photoemission spectroscopy. The formed surface layer even allows for a layer-by-layer degradation and acts as a protection barrier against further additional loss of I atoms and the consequent hydration of the inner part of samples. We demonstrate that light is the most critical external factor accelerating 2D perovskite degradation processes in ambient air and thus affecting their long-term stability. We conclude in this work that perovskite material structural engineering together with their surface passivation or encapsulation strategical techniques applied is an essential step for their further application into long-term stable commercial devices.

Regulating thermal management by a CsPbClBr2/Ag hybrid microcavity for stable room temperature blue lasing with low threshold

Realization of long-term stable lasing from all-inorganic perovskite supercrystals is highly desirable for practical applications in optoelectronic devices. However, lasing from perovskite supercrystals excited by continuous wave laser light remains a challenge due to the photoluminescence degradation induced by thermal accumulation. Here, we report highly stable lasing with low threshold fom a CsPbClBr2 supercrystal placed on a thin Ag film, which form a CsPbClBr2/Ag microcavity, by managing the thermal distribution inside the CsPbClBr2 supercrystal. Combined numerical simulations and lifetime measurements, the localized electric field in such a hybrid microcavity leads to a spatially localized temperature distribution, which plays a crucial role in suppressing the thermal accumulation on the surface and in eliminating non-radiative recombination defects. The effective thermal management in the hybrid microcavity renders highly stable lasing with low threshold under the irradiation of continuouw wave laser light. Our findings provide a feasible and universal approach to the development of long-term stable perovskite laser.

A donor-acceptor π-stacked multifunctional Eu-MOF based on a novel viologen-like photosensitive ligand: Degradation of tetracycline, photochromism, and photoluminescence

The photosensitive building blocks of photochromic MOFs are mostly 4,4′-bipyridine. However, the linear structure and kind of 4,4′-bipyridine derivatives limit the development of its properties and applications. Therefore, a “Y"-shaped 2,4,6-tri (4-pyridyl)-1,3,5-triazine derivative ([H3p-Batpt]Cl3, TPT) with high conjugation, bare nitrogen and oxygen sites that was selected as a novel photosensitive ligand to replace the traditional 4,4′-bipyridine ligand for photochromic MOFs. Then, [H3p-Batpt]Cl3 was combined with EuIII and terephthalic acid (H2TPA) to construct a multifunctional Eu-MOF [Eu2 (p-Batpt) (TPA)3(H2O)]n (1). 1 possess degradation of tetracycline (TC), photochromic and photoluminescence properties. The colored 1 (1P) after irradiation with UV–vis light (300 W, Xe-lamp) is difficult to fade due to donor-acceptor (D-A) π-π and radical-π interactions. In addition, 1 is used in photocatalysis because it is an excellent N-type semiconductor. The TC degradation rate of 1 can reach 67.42 % under visible light and be recycled six times. Interestingly, the TC degradation rate of 1P was 6.78 % higher than that of 1. Electrochemical tests show that 1P has higher charge separation efficiency and a smaller band gap. The free radicals capture and ESR experiments of 1 revealed that holes (h+) played a leading role in the photocatalytic degradation of TC. This research expands the application of photochromic MOFs and provides a reference for removing organic pollutants.

Enhancement of the alloyed CdZnSeS/ZnS quantum dots photoluminescence by thiol ligands capping

Most of the existing hydrophilization techniques for the semiconductor quantum dots (QDs) lead to degradation of photoluminescence (PL). Therefore, for the applying of QDs in the areas requiring their stability in water media (e.g. bio- and chemical analysis, labeling and sensing), it is often necessary to find a balance between high stability, good optical properties, and difficulty of acquiring. This article describes simple, fast, and easy scalable methods for alloyed CdZnSeS/ZnS QDs ligand exchange using 2-mercaptoethanol, thioglycolic, 3-mercaptorpopionic and dihydrolipoic acids. The proposed ligand exchange techniques provide the enhancement of the QDs photoluminescence intensity in contrast to most of other ligand exchange procedures on the QDs surface. In optimized conditions the twofold photoluminescence quantum yield increase compared to the initial hydrophobic CdZnSeS/ZnS QDs was achieved. Hydrophilized nanoparticles maintained colloidal stability for a period more than 13 months. The suggested mechanism of the PL increase is the passivation of the QDs surface with molecules containing a thiol group. The combination of the proposed effective CdZnSeS/ZnS QDs synthesis and modification methods shows the prospect of their implementation as basic luminescent material for a wide range of applications.

Photoluminescence and photocatalytic degradation studies of Zn-based nanoparticles on malachite green dye

Water, the most fundamental source of life, is contaminated by various organic pollutants, especially organic dyes from the dying industry. The photocatalytic degradation of malachite green (MG) was studied using a zinc-based metal-organic framework (Zn-BTC MOF) and ZnO. Thermally decomposing Zn-MOF synthesized ZnO and its structural and optical properties were analyzed using various spectroscopic techniques. This article focuses primarily on the wavelength-dependent photoluminescence properties of Zn-MOF and ZnO materials and their role in the photocatalytic degradation of MG dye in water. Zn-MOF and ZnO photocatalysts exhibited a photodegradation efficiency of approximately 99% after 40 min of visible light exposure. Based on kinetic experiments, the degrading efficiency of these catalysts followed pseudo-first-order reaction kinetics with a correlation of R2 = 0.99 and a rate constant of 0.031 min−1. This manuscript is helpful to researchers working on ZnO and Zn-MOF materials for photocatalytic and environmental applications.

Photoluminescence and Photocatalytic Degradation of Methylene Blue and Methyl Red using Pr3+ Doped CdS Nanoparticles

Photoluminescence and Photocatalytic Degradation of Methylene Blue and Methyl Red using Pr3+ Doped CdS Nanoparticles

Enhancing photocatalytic activity: Investigating the synthesis and characterization of BiVO4/Cu2O/graphene ternary nanocomposites

In this study, BiVO4,Cu2O, and grapheneconcentrations have been carefully monitored during the hydrothermalsynthesis of the BiVO4/Cu2O/graphenenanocomposites. The impacts of different concentrations of graphene, time duration and heat treatment temperature have been investigated for synthesized samples. By various characterizations UV–Vis, photoluminescence (PL), FTIR, SEM, XRD and dye degradation, the optical characteristics, vibrational analysis, morphology, structural analysis and photocatalytic activity of the samples examined respectively. The nanocompositeBiVO4/Cu2O with different graphene ratios, the influence on the photocatalytic efficiency and stability of optimal sample has been investigated. BiVO4 and Cu2O concentrations had an impact on the stability of the monoclinic phase of BiVO4, according to X-ray diffraction (XRD) patterns. Nanosheets compositeswith 100 nm average size of nanosheets has observed in SEM micrographs. The e--h+ recombination rate for this sample was lowest according to the PL findings. Also, the optimized sample BiVO4/Cu2O/G5, after 120 min in the visible light spectrum, achieved the greatest degradation of 96% for rhodamine-B (RhB) and 98% for tetracycline (TC) by using optimized photocatalyst BiVO4/Cu2O/G5. Utilizing scavengers, the photocatalytic mechanism has been studied. Recyclability test has been performed to pattern the stability by XRD for optimal sample. To explore the photocatalytic performance, the kinetics of the degradation of RhB and TC have also been examined.

P‐123: Double Emitting Layer Structure for high efficiency and ultra‐stable blue Triplet‐Triplet Annihilation OLED

By using the double emitting layer (DEML) structure in a blue triplet‐triplet annihilation organic light‐emitting diode (TTA‐OLED), maximum external quantum efficiency (EQEmax) of 16.1% with CIE coordinates of (0.135, 0.188) and half‐lifetime of 224,000 hours at initial luminance of 1,000 cd/m2was achieved. The degradation mechanism of TTA‐OLEDs was also investigated by conducting photoluminescence degradation experiment.

Synthesis, photoluminescence and photocatalytic degradation of antibiotics by a new Zn(II)-coordination polymer

A new Zn(II)-based coordination polymer (CP) having the composition [Zn3(L)2(phen)2] (1) (H2L=3,3ʹ-(1,4-phenylene-bis-(methyleneoxy)dibenzoic acid, phen= 1,10-phenanthroline) has been synthesized using mixed ligand strategy under solvothermal conditions. 1 has been characterized by microanalyses, FTIR, UV–Vis spectroscopy, and single X-ray diffraction technique. The structural analyses show that 1 possess 2D supramolecular framework that is formed by weak interactions between its chains. The optical band of 2.7 eV suggests that 1 possesses semiconducting property. 1 has been used as photocatalyst to photodegrade varied antibiotics, amongst which it exhibits best photodegradation of the nitrofurazone antibiotic. A plausible photocatalytic degradation pathway has been proposed by radical tapping experiments and theoretical calculations.

Monolithic Multicolor Emissions of InGaN-Based Hybrid Light-Emitting Diodes Using CsPbBr3 Green Quantum Dots.

To address the increasing demand for multicolor light-emitting diodes (LEDs), a monolithic multicolor LED with a simple process and high reliability is desirable. In this study, organic-inorganic hybrid LEDs with violet and green wavelengths were fabricated by depositing CsPbBr3 perovskite green quantum dots (QDs) as the light-converting material on InGaN-based violet LEDs. As the injection current was increased, the total electroluminescence (EL) intensities of the hybrid LEDs increased, whereas the light-converted green emission efficiency of the CsPbBr3 QDs decreased. The maximum green-to-violet EL spectral intensity ratio of the hybrid LEDs with CsPbBr3 QDs was achieved with the injection current of <10 mA. Moreover, the EL spectral ratio of the green-to-violet emission decreased at an injection current of 100 mA. The light-conversion intensity of the CsPbBr3 QDs decreased linearly as the junction temperature of the hybrid LEDs was increased with increasing injection current, similar to the temperature-dependent photoluminescence degradation of CsPbBr3 QDs. In addition, the junction temperature of the hybrid LED was minimized by pulse injection to suppress the thermal degradation of QDs and increase the light conversion efficiency to green emission. Therefore, the overall emission spectrum color coordinates of the hybrid LEDs exhibited a red shift from violet to blue in the low-current region and a blue shift toward violet as the green emission of the QDs was decreased above 10 mA.

GaN damage-free cyclic etching by sequential exposure to Cl2 plasma and Ar plasma with low Ar+-ion energy at substrate temperature of 400 °C

Damage-free atomic layer etching (ALE) of GaN was demonstrated using a cyclic process in which the chlorinated layer formed by Cl2 plasma exposure was removed by exposure to Ar plasma with energy-controlled ions when the substrate temperature was maintained at 400 °C. The layer chlorinated at 400 °C by Cl2 plasma exposure was found to be thinner than that chlorinated at 25 °C. Therefore, in the case of an Ar+-ion energy of 70 eV, the “ALE synergy” parameter, which quantifies the degree to which a process approaches the ideal ALE regime, decreased from 86% at a substrate temperature of 25 °C to 24% at a substrate temperature of 400 °C. A substrate temperature of 400 °C promoted etching even at the lower ion energy of 40 eV, thereby resulting in a higher ALE synergy of 62%. The vertical etching profile with no degradation of photoluminescence near the band edge on the etched surface was then observed. The proposed high-temperature ALE method is promising for realizing a vertical pattern profile via damage-free etching of GaN.

Large photoluminescence enhancement in the chlorophyll from the energy transfer in perovskite–chlorophyll hybrid derivatives

Determining the photophysical processes for biomaterial–semiconductor systems has been beneficial for developing optoelectronic devices that exhibit biodegradability and biocompatibility. Here, we systematically investigated the optical properties and photophysical mechanisms of CsPbBr3 nanoparticles (NPs)-incorporated chlorophyll material. Steady-state photoluminescence (PL) studies reveal a large fluorescence enhancement in the chlorophyll once the perovskite was incorporated in the pristine chlorophyll with an associated PL quenching of the CsPbBr3 emission. A spectral overlap was measured from the PL and absorption spectra of CsPbBr3 NPs and chlorophyll indicative of a Förster-type resonance energy transfer (FRET). Using time-resolved PL, faster PL decay curves were observed from the CsPbBr3 NPs in the mixture suggesting that most of its energy was transferred to the chlorophyll. The corresponding Jablonski diagram was built and the energy transfer parameters, such as FRET efficiencies and transfer rates, were calculated to fully explain the FRET process. Slow PL degradation for the mixtures was also observed, highlighting the advantage of the FRET proposed. The demonstration of the photophysical mechanism in biomaterial–semiconductor systems is influential in improving the performance of emerging bio-inspired optoelectronic devices.

Enhancing oxygen/moisture resistance of quantum dots by short-chain, densely cross-linked silica glass network

Quantum dots (QDs) are facing significant photoluminescence degradation in moisture environment. In QDs-silicone composites, the poor water resistance of silicone matrix makes it easy for water and oxygen molecules to erode QDs. To tackle this issue, we proposed a new QDs protection strategy by introducing short-chain silica precursors onto the QDs’ surface, so that a dense silica passivation layer could be formed onto the QDs nanoparticles. Sol-gel method based on 3-aminopropyl triethoxysilane (APTES), 3-mercaptopropyl trimethoxysilane (MPTMS), and 3-mercaptopropyl triethoxysilane (MPTES) were adopted to prepare the uniform and crack-free QDs-silica glass (QD-glass). Because of the crosslinking of short-chain precursors, the formed silica glass possesses 38.6% smaller pore width and 68.6% lower pore volume than silicone, indicating its denser cross-linked network surrounding QDs. After 360 h water immersion, the QDs-glass demonstrated a 6% enhancement in red-light peak intensity, and maintained a stable full width at half maximum (FWHM) and peak wavelength, proving its excellent water-resistant ability. However, the conventional QDs-silicone composites not only showed a decrease of 75.3% in red-light peak intensity, but also a broadened FWHM and a redshifted peak wavelength after water immersion. QDs-glass also showed superior photostability after 132 h exposure to blue light. Red-light peak intensity of QDs-glass remained 87.3% of the initial while that of QDs-silicone decreased to 19.8%. And the intensity of QDs-glass dropped to 62.3% of that under 20 °C after thermal treatment of 160 °C. Besides, under increasing driving currents, the light conversion efficiency drop of QDs-glass is only one fifth that of QDs-silicone. Based on the QDs-glass, the white light-emitting diodes was achieved with a high luminous efficiency of 126.5 lm W−1 and a high color rendering index of 95.4. Thus, the newly proposed QD-glass has great significance in guaranteeing the working reliability of QDs-converted devices against moisture and high-power environment.

Low‐Power‐Consumption, Reversible 3D Optical Storage Based on Selectively Laser‐Induced Photoluminescence Degradation in CsPbBr3 Quantum Dots Doped Glass

AbstractIn recent years, inorganic lead halide perovskite quantum dots have been used in various optoelectronic fields for their excellent luminescence properties, such as narrow emission bands, ultra‐wide tunable emission wavelength, and high quantum efficiency. In this paper, different from luminescence optimization in most research, luminescence degradation of perovskite quantum dots is addressed by femtosecond laser irradiation and successfully used for three‐dimensional data storage in CsPbBr3 quantum dots doped glass. Photoluminescence (PL) degradation can be finely modulated by adjusting the laser parameters. PL degradation mechanism, investigated by optical spectroscopy and morphology characterization, is attributed to laser‐induced decomposition, recrystallization, and defection of CsPbBr3 quantum dots. Laser‐induced PL degradation and the followed PL recovery by heat treatment are repeated for several cycles, showing good reversibility. Multilayer PL degradation patterns are written into the glass and read out without crosstalk, indicating high‐reliability 3D optical storage characteristics. Amazingly, PL degradation can be induced by just a low‐energy single laser pulse with estimated subpicosecond writing time per bit, demonstrating its potential in high‐speed, low‐power consumption 3D optical storage.

Improving the thermal resistance of fluorescent CsPb(Br,I)3 perovskite quantum dots by surface modification with perfluorodecanoic acid.

CsPb(Br,I)3 quantum dots (QDs) show application potential for optoelectronic devices. However, their thermal degradation is a significant problem. In this work, the effects of perfluorodecanoic acid (PFDA) modification on the photoluminescence (PL) and thermal resistance of CsPb(Br,I)3 QDs were evaluated. The PL intensity of oleic-acid-modified quantum dots (OA-QDs) in toluene decreased drastically upon heating at 100°C. The PL quantum yield of the QDs increased from 69.6% to 77.4% upon modification with PFDA. Furthermore, the PL intensity of the QDs modified with PFDA (PFDA-QDs) increased to 140.6% upon heating, because of the reduction of surface defects upon adsorption of PFDA and its optimized adsorption state. A solid-film PFDA-QDs sample heated at 80°C for 4 h showed temporary PL enhancements for the OA-QDs and PFDA-QDs films to 445% and 557% of their initial values, respectively, upon heating for 0.25 h. This was attributed to the optimized adsorption states of the surface ligands. PFDA-QDs film maintained 354% after 4 h of heating, whereas that of OA-QDs film was 104%. Thus, PFDA modification enhances PL intensity and suppresses PL degradation under heating, which is important for wavelength converters for optoelectronic device applications.

First-principles study of electronic properties of amine ligand-capped CsPbBr3 surface with organo-metallic alumina precursor treatment

Water and oxygen stability has been one of the major bottlenecks in practical application of perovskite quantum dots (PeQDs). Recently, ultra-thin alumina via atomic layer deposition (ALD) has been used as protective coating to improve the stability of PeQDs. However, the use of organo-metallic trimethylaluminum (TMA) precursor is typically accompanied by undesirable photoluminescence quenching of PeQDs. We investigate in detail the interaction mechanism between TMA and amine ligands-capped PeQDs to shed light on the origin of such quenching. First-principles calculations reveal that TMA is highly reactive to insert into amine ligands and PeQDs, which disrupts the bonding between ligand and the PeQDs surface. The demethylation of the insertion product would induce substantial trap states on the PeQDs surface, resulting in the degradation of photoluminescence. Methyl aluminum diisopropoxide (MADI) with asymmetric structure is proposed as an ALD precursor for the treatment of PeQDs. Due to the tight binding of the isopropyl groups to the Al atom, MADI can effectively avoid successive dissociation after reaction with surface ligands, avoiding the formation of trap states. This work highlights the importance of precursor engineering for ligand passivation and provides guidance to the design of precursors with minimal trap-states for highly efficient and stable PeQDs.

Study on interfacial interactions and optoelectronic properties of MEH-PPV/SnO2 hetero-structure

The exciton dynamics in nanocomposites of tin oxide (SnO2) nanoparticles with a conjugated polymer (poly (2-methoxy-5-(2'-ethylhexyloxy) 1,4-phenylenevinylene) (MEH-PPV) have been investigated by steady-state, time-resolved photoluminescence (PL) spectroscopy and cyclic voltammetry (CV) analysis. SnO2 is an air-stable, optically transparent, electrically conductive deep valance band metal oxide which is suitable as an electron-accepting material in organic photovoltaics (PVs). Results reveals that SnO2 is an efficient electron-accepting material in comparison with titanium dioxide (TiO2) nanoparticles. Efficient charge separation takes places at SnO2/MEH-PPV interfaces when the polymer is excited, leading to enhancement in quenching of PL efficiency (10%) and shortening of the measured PL lifetime. In addition, the reduction in recombination rate of MEH-PPV/SnO2 nanocomposite show that the incorporation of nanoparticles in the polymer chain reduce disorders in the polymer chains. The blue-shift in the absorbance and emission maxima denotes that the process of in situ polymerization resulted in shortening of polymer chain conjugation. The electrochemical analysis for MEH-PPV/SnO2 nanocomposite shows increase in current density compared to MEH-PPV/TiO2 and pristine MEH-PPV. Moreover, the PL degradation experiments showed that MEH-PPV/SnO2 exhibited enhanced stability. MEH-PPV/SnO2 film attained 50% of the original intensity in ∼10 d, while pristine MEH-PPV and MEH-PPV/TiO2 exhibited half-life of ∼5 d when exposed to an ambient environment. The effect of TiO2 nanoparticles to stabilize MEH-PPV is though less important than that of SnO2. Thus MEH-PPV/SnO2 nanocomposite with enhanced absorbance, conductivity, stability and lowered bandgap formed an effective type-II band structure suitable for the PV active layer.

Eight semiconducting MOFs constructed with conjugated ligands and d-metals (Cd, Zn, Co and Ni) serve as functional materials for oxygen evolution reactions, photocatalytic degradation of dyes and photoluminescence

We constructed eight MOFs with semiconductor behavior, discussed their structures in detail, and explored their practical applications.

Synthesis of ZrO2:Dy3+ Nanoparticles: Photoluminescent, Photocatalytic, and Electrochemical Sensor Studies

Solution combustion was employed to create a series of ZrO2:Dy3+ (1-11 mol percent) nanoparticles (NPs) using oxalyl dihydrazide (ODH) as the fuel. ZrO2:Dy3+ NPs were subjected to calcination at about 700°C. ZrO2:Dy3+ NPs comprised of 1 to 11 mol% of Dy3+ were characterized by employing the X-ray diffraction (XRD), transmission electron microscopic (TEM), UV-visible, and X-ray photoelectron spectroscopic (XPS) techniques. The crystallite diameters of 1 to 11 mol% ZrO2:Dy3+ NPs were observed to range from 8.1 nm to 16.3 nm, exhibiting spherical shape. According to BET tests, the pore volume of ZrO2:Dy3+ NPs was determined to be 100.129 cm3/g. The mean pore diameter of ZrO2:Dy3+ NPs was determined to be 4.803 nm from the Barrett-Joyner-Halenda (BJH) plot. The photoluminescence and photocatalytic dye degradation properties of ZrO2:Dy3+ NPs were investigated. The acid red 88 (AR88) dye was applied to appraise the photocatalytic activities of the NPs under UV irradiation. ZrO2:Dy3+ NPs with 3 mol% Dy3+ exhibited improvised photocatalytic activity due to the operative departure of charge carriers. The electrochemical examination of ZrO2:Dy3+ NP modified carbon paste electrode in 0.1 N HCl demonstrated considerable redox potential output, as evidenced by cyclic voltammetric and amperometric measurements. The electrochemical sensor studies on ZrO2:Dy3+ NPs exhibited potentiality towards sensing of highly toxic metals like mercury and lead.

CsPbBr3 Nanoplatelets: Synthesis and Understanding of Ultraviolet Light-Induced Structural Phase Change and Luminescence Degradation

CsPbBr3 perovskite nanocrystals (mainly nanoplatelet morphology) have attracted attention due to their promising applications in optoelectronic devices. However, ultraviolet (UV) light exposure to these materials is one of the major factors for the degradation of halide perovskite nanocrystals, which needs to be studied to improve stability and boost performance. In this study, we synthesized CsPbBr3 perovskite nanoplatelets utilizing a hot injection method. The UV illumination effect on luminescence and structural properties of perovskite CsPbBr3 nanoplatelets were studied in detail. Under UV light illumination, less-emissive phases like CsPb2Br5 were observed within 10 h. However, long-term (i.e., 48 h) illumination of UV light resulted in the formation of some trace of PbCO3 and PbO phases that causes further degradation of perovskite CsPbBr3 nanoplatelets. This was verified by a significant decrease in photoluminescence (PL) intensity. Interestingly, UV light treated samples exhibited a stable CsPb2Br5 phase, which was observed after aging for a long period (∼9 months) of time that showed no further degradation. Furthermore, X-ray diffraction and full-width half maxima results confirmed an increase in crystalline size with illumination time increase. Obtained results strongly indicate that the UV light-induced PL degradation and trap state formation causes a synergistic effect of photo annealing in the presence of oxygen and moisture.